departures from controlled flight that do not result in traditional
spins. This is done in the military and for civilian aerobatic
airplanes to address the situation where a mistake during a planned
maneuver results in departing controlled flight. The FAA can envision a
flight control system that could prevent departures from all approved
maneuvers. To the FAA's knowledge, the F-16 flight control system has
been very successful in preventing inadvertent departures from
controlled flight even though these airplane are frequently flown
``acrobatically.'' For these reasons, the FAA may allow certification
of a new airplane for dual use even if the airplane is not approved for
spins. However, an applicant proposing a system, such as a flight
control system that could prevent departure from controlled flight
during normal operations, should expect to work with the FAA to
thoroughly address FAA concerns for safe margins from inadvertent
departure from controlled flight.
    Proposed Sec.  23.215(d) would have precluded airplanes certified
for aerobatics from having spin characteristics that would result in
unrecoverable spins due to pilot disorientation or incapacitation or
any use of the flight or engine power controls. Upon further
reflection, the FAA revises the proposed rule language to require spin
characteristics in airplanes certified for aerobatics to recover
``without exceeding limitations.'' The FAA inadvertently omitted this
clause from proposed Sec.  23.215(d) (nowSec.  23.2150(e)), which was
intended to capture the safety intent of former Sec.  23.221(c). Former
Sec.  23.221(c) required the applicable airspeed limits and limit
maneuvering load factors not to be exceeded. Additionally, including
this clause in the requirement will better align the FAA language with
EASA's NPA language.
    The NTSB commented that while it supports reducing the rate of loss
of control accidents in general aviation, it is unclear how proposed
Sec. Sec.  23.200 and 23.215 would have accomplished this. The NTSB
explained that the only link it sees to reducing loss of control
accidents is the change to VMC and asked the FAA to clarify
exactly how the revisions will reduce loss of control accidents.
    The FAA notes that the NPRM included a substantial discussion
explaining how the FAA envisions the rule reducing loss of control
accidents. The new rules allow alternative approaches that an applicant
may use, ranging from a stick pusher to full spin resistance. Adding
flexibility to the rule will allow alternate approaches to address
inadvertent departure by using combinations of new technology not
addressed in the former requirements. These alternatives will be
addressed in means of compliance. There is no ``exact'' approach to
meet the new rule because the objective is to encourage new approaches
to loss of control that are more effective than the ones that are
failing us today.
    Additionally, the NTSB submitted detailed comments on the stall
departure characteristic exception in the ASTM standard. The FAA will
address these comments in the AC because these comments are on the
acceptability of an ASTM standard as a means of compliance rather than
on the proposed rule.
l. Ground and Watering Handling Characteristics (Proposed Sec.  23.220/
Now Sec.  23.2155)
    In the NPRM, proposed Sec.  23.220 (now Sec.  23.2155) would have
required airplanes intended for operation on land or water to have
controllable longitudinal, and directional handling characteristics
during taxi, takeoff, and landing operations. Proposed Sec.  23.220
would have also required an applicant to establish a maximum wave
height shown to provide for controllable longitudinal, and directional
handling characteristics and any necessary water

handling procedures for those airplanes intended for operation on
water.
    Textron and the Associations noted that the FAA proposed to remove
the prescriptive requirements related to establishing demonstrated
crosswind capability from former Sec.  23.233, but proposed to retain
similar requirements for water operations to establish wave height
criteria. These commenters stated that operational specificity related
to water landings should be addressed in means of compliance standards
and recommended that the FAA not adopt proposed Sec.  23.220(b).
    The FAA agrees with the commenters that proposed Sec.  23.220(b)
would have been overly prescriptive for water operations and that it
would be more appropriate as a means of compliance. While proposed
Sec.  23.220(a) would have included the top-level safety requirements
for both land and water operations, proposed Sec.  23.220(b) would have
been inconsistent with the approach taken for land airplanes as it
would have contained prescriptive requirements only for airplanes
intended for operation on water. Accordingly, the FAA is not adopting
proposed Sec.  23.220(b). The information necessary to comply with
proposed Sec.  23.220(a) (now Sec.  23.2155 in its entirety) and the
method to communicate that information to the pilot will be addressed
in means of compliance with this section.
    EASA also recommended that the FAA not adopt proposed Sec.
23.220(b). EASA explained that the AFM requirements in subpart G should
cover ``how-to'' information and how that information is provided to
the pilot, as proposed in the NPRM. Therefore, proposed Sec.  23.220(b)
should not require what must be included in the AFM.
    The FAA agrees with EASA that the information is more appropriately
addressed in the AFM means of compliance. The AFM requirements are
located in subpart G.
m. Vibration, Buffeting, and High-Speed Characteristics (Proposed Sec.
23.225/Now Sec.  23.2160)
    In the NPRM, proposed Sec.  23.225 (now Sec.  23.2160) would have--
     Precluded vibration and buffeting from interfering with
the control of the airplane or causing fatigue to the flightcrew, for
operations up to VD/MD;
     Allowed stall warning buffet within these limits;
     Precluded perceptible buffeting in cruise configuration at
1g and at any speed up to VMO/MMO, except stall
buffeting for high-speed airplanes and all airplanes with a maximum
operating altitude greater than 25,000 feet (7,620 meters) pressure
altitude;
     Required an applicant seeking certification of a high-
speed airplane to determine the positive maneuvering load factors at
which the onset of perceptible buffet occurs in the cruise
configuration within the operational envelope and preclude likely
inadvertent excursions beyond this boundary from resulting in
structural damage; and
     Required high-speed airplanes to have recovery
characteristics that do not result in structural damage or loss of
control, beginning at any likely speed up to VMO/
MMO, following an inadvertent speed increase and a high-
speed trim upset.
    Textron and the Associations noted that the language from which
proposed Sec.  23.220(a) originated (former Sec.  23.251) included the
term ``excessive fatigue,'' rather than ``fatigue.'' These commenters
recommended that the FAA use the term ``excessive fatigue'' in proposed
Sec.  23.220(a). Textron explained that by omitting the term
``excessive,'' any perceptible level of fatigue could be considered
unacceptable and the proposal would result in an unwarranted change in
standards for vibration.
    The FAA agrees with the commenters and is adding the term
``excessive'' to Sec.  23.2160(a).
    ICON contended that proposed Sec.  23.225(b) would have been fine
for landplanes, but not for seaplanes because seaplanes, with their
hull step, will always have some buffet in cruise. Additionally, ICON
noted that airplane with windows removed will have perceptible
buffeting at all speeds.
    The FAA agrees with ICON that seaplanes and floatplanes routinely
operate with a limited amount of buffet during normal operation. The
FAA did not intend for proposed Sec.  23.225(b) to increase the level
of safety over former Sec.  23.251, which allowed for the limited
buffeting normal to seaplanes and floatplanes. Historically, this level
of buffeting has not interfered with the control of the airplane or
caused excessive fatigue to the pilot. Because the proposed rule
language originated from former Sec.  23.251, the FAA finds that it
does not create a new certification burden on applicants with seaplanes
or floatplanes. Accordingly, the FAA adopts the language as proposed.
Furthermore, airplanes approved for operations without doors or
windows, or those that allow the windows to open in flight, were not
intended to be addressed under this rule.
    Textron and the Associations noted that the former requirement for
a high-speed trim upset (former Sec.  23.255) applied to designs with
adjustable horizontal stabilizers. However, the FAA did not specify
whether proposed Sec.  23.220(d)(2) would have been limited to
airplanes with adjustable horizontal stabilizers. Textron explained
that, as proposed, Sec.  23.220(d)(2) would have contained an
additional requirement for high-speed airplanes that did not have
trimmable horizontal stabilizers. The commenters recommended the FAA
limit the application of proposed Sec.  23.220(d)(2) to airplanes that
incorporate a flight adjustable horizontal stabilizer.
    The FAA intended to keep this requirement as general as possible,
not to propose a new requirement on high-speed airplanes that lacked
trimmable horizontal stabilizer. As stated in the NPRM, the FAA
intended proposed Sec.  23.220(d)(2) (now Sec.  23.2160(d)(2)) to
address the current safety intent of former Sec.  23.255, which applied
only to airplanes that included trimmable horizontal stabilizers. The
FAA adopts language in Sec.  23.2160(d)(2) to clarify that the
requirement applies only to airplanes that incorporate trimmable
horizontal stabilizers.
n. Performance and Flight Characteristics Requirements for Flight in
Icing Conditions (Proposed Sec.  23.230/Now Sec.  23.2165)
    In the NPRM, proposed Sec.  23.230 (now Sec.  23.2165) would have
required--
     An applicant requesting certification for flight in icing
conditions to demonstrate compliance with each requirement of this
subpart. Exceptions to this rule would have been requirements
applicable to spins and any requirement that would have to be
demonstrated at speeds in excess of 250 KCAS, VMO or
MMO, or a speed at which an applicant demonstrates the
airframe would be free of ice accretion;
     The stall warning for flight in icing conditions and non-
icing conditions to be the same.
     An applicant requesting certification for flight in icing
conditions to provide a means to detect any icing conditions for which
certification is not requested and demonstrate the airplane's ability
to avoid or exit those conditions; and
     An applicant to develop an operating limitation to
prohibit intentional flight, including takeoff and landing, into icing
conditions for which the airplane is not certified to operate.
    Proposed Sec.  23.230 would have also added optional icing
conditions where a manufacturer may demonstrate its airplane can either
safely operate in, detect and safely exit, or avoid. Finally,

proposed Sec.  23.230 would have only applied to applicants seeking
certification for flight in icing.
    NJASAP stated it viewed proposed Sec.  23.230 as a safety
enhancement and noted that several accidents have demonstrated a
benefit to having one stall standard--meaning the airplane should be
able to remain largely free of ice in conditions within which it is
certified to operate. The NTSB stated that adopting proposed Sec. Sec.
23.230 and 23.1405 will likely result in Safety Recommendation A-96-54
being classified as ``Closed--Acceptable Action.''
    Textron and the Associations asked the FAA to clarify that proposed
Sec.  23.230(a) applies to the airplane's ice protection system when it
is operating normally, not when it is in a failed or degraded mode.
Therefore, rather than requiring the applicant to demonstrate the
requirements of proposed paragraphs (a)(1) and (a)(2), the Associations
recommended that the FAA require the normally-operating airplane ice
protection systems to include the requirements of proposed paragraphs
(a)(1) and (a)(2).
    The FAA agrees with the comments made by the Associations and
Textron, and the FAA adopts language to clarify that Sec.  23.2165(a)
applies to the normal operation of an ice protection system.
Accordingly, Sec.  23.2165(a) now requires the applicant to demonstrate
the requirements of paragraphs (a)(1) and (a)(2) under the normal
operation of the ice protection system.
    The FAA is also changing the language in Sec.  23.2165(a) to
clarify that Sec.  23.2165 applies to an applicant who requests
certification for flight in icing conditions defined in part 1 of
appendix C to part 25, or to an applicant who requests certification
for flight in these icing conditions and any additional atmospheric
icing conditions. This change better reflects the FAA's intent.\27\
---------------------------------------------------------------------------

    \27\ 81 FR 13452, 13462
---------------------------------------------------------------------------

    Additionally, the FAA is using the phrase ``must show'' rather than
``must demonstrate'' in Sec.  23.2165(a), because ``must demonstrate''
may be interpreted as requiring a flight test, as Textron suggested in
its comment on proposed Sec.  23.230(b) (discussed later). This change
is consistent with the NPRM, which explained that demonstration, as a
means of compliance, may include design review and/or analysis and does
not mean flight tests are required.\28\
---------------------------------------------------------------------------

    \28\ 81 FR 13452, 13493
---------------------------------------------------------------------------

    The FAA is also adding the never-exceed speed (VNE) to
the exception in Sec.  23.2165(a), under paragraph (a)(1)(ii), to
correct an inadvertent omission in the proposal. Because proposed Sec.
23.230(a)(1)(ii) was intended to apply to both piston and turbine
airplanes, the addition of VNE is necessary as the proposed
VMO/MMO would only have applied to turbine
airplanes. This change from what was proposed is consistent with the
current guidance in AC 23.1419-2D.
    BendixKing, Daher,\29\ the Associations, Kestrel, and Textron all
requested clarification of the wording of proposed Sec.  23.230(a)(2),
which proposed that the applicant must demonstrate that the stall
warning for flight in the icing conditions and non-icing conditions is
``the same.'' Several of the commenters explained that the stall
warning in icing conditions needs to provide a similar notification as
the stall warning in non-icing conditions, but it does not need to
occur in the same way.
---------------------------------------------------------------------------

    \29\ In its comment, Daher quoted 23.230(a)(2) but attributed
that quote to 23.300
---------------------------------------------------------------------------

    Textron similarly stated that proposed Sec.  23.230(a)(2) could be
interpreted as indicating that the stall warning must be the same in
all of its aspects, which should not be the intent. Textron explained
that the stall warning system in icing conditions cannot be the same as
in non-icing conditions because some designs require a different angle
of attack schedule in icing to obtain the same airspeed margin between
stall warning and stall. Textron recommended requiring ``the means by
which stall warning is provided to the pilot'' to be the same in icing
and non-icing conditions.
    In response to the comments on proposed Sec.  23.230(a)(2), the FAA
did not intend to require the stall warning to be the same in all
material aspects for flight in icing conditions and non-icing
conditions. Rather, the FAA intended proposed Sec.  23.230(a)(2) to
require the same type of stall warning, such as an artificial stall
warning system or an aerodynamic buffet. Therefore, the FAA adopts
Textron's recommendation. Accordingly, Sec.  23.2165(a)(2) now requires
the means by which the stall warning is provided to the pilot to be the
same in both icing and non-icing conditions. This change from the
proposal addresses the other commenters' concerns by clarifying that
the type of stall warning provided to the pilot, rather than the design
of the stall warning system, must be the same.
    Textron recommended replacing the words ``must demonstrate'' with
the words ``must show'' in proposed Sec.  23.230(b), because the former
typically implies compliance by flight testing, whereas the latter
allows more than one means of compliance. Similarly, the Associations
commented that proposed Sec.  23.230(b) should ensure the design
includes a means to safely avoid and exit icing conditions. However,
the FAA should not require the applicant to ``demonstrate the
airplane's ability'' to avoid or exit icing conditions because the
means by which the airplane safely avoids or exits icing conditions may
not have to be demonstrated under part 21. The commenters noted that
amended designs, for example, may use similarity to a previously
approved design to show compliance.
    The FAA agrees that ``must demonstrate'' in proposed Sec.
23.230(b) may be interpreted as requiring a flight test. Because the
FAA did not intend to preclude other means of compliance, the FAA
adopts the phrase ``must show,'' as recommended by Textron.
Accordingly, Sec.  23.2165(b) now requires an applicant requesting
certification for flight in icing conditions to show the airplane's
capability to avoid or exit icing conditions for which certification is
not requested.
    Kestrel supports categorizing SLD as an icing condition, but noted
that guidance in AC 23.1419-2D is currently used on part 23 icing
certification programs to establish SLD detection cues and exit
procedures. Kestrel asked the FAA to clarify whether this guidance will
continue to be an acceptable means of compliance for the ice detection
requirement.
    The NPRM stated ``many manufacturers already have equipped recent
airplanes with technology to meet the standards for detecting and
exiting SLD conditions in accordance with current FAA guidance.''
Although systems to detect SLD are being developed, none have been
certified. Inclusion of the pilot cues as listed in AC 23.1419-2D into
the AFM have been an acceptable means to detect SLD, and will continue
to be an acceptable means of compliance to Sec.  23.2165(b).
    ANAC questioned whether proposed Sec.  23.230(c) was intended to
prohibit flight into known icing conditions or forecast icing
conditions. ANAC recommended including the term ``known'' before
``icing conditions.''
    The FAA agrees with ANAC's position that only ``known'' icing
conditions should be prohibited. However, Sec.  23.2165(c) prohibits
intentional flight into icing conditions. Because the term
``intentional'' implies that the icing conditions are known, the FAA
finds it unnecessary to include the term ``known'' before ``icing
conditions.'' Accordingly, the FAA

adopts the language in Sec.  23.2165(c) as proposed.
    An individual commenter appeared to criticize the FAA for not
requiring de-icing to work and suggested that ``[a] wind tunnel at the
far North or South may be enough for a conclusive test.'' In response
to the individual commenter, an icing tunnel is a standard means of
compliance to test ice protection systems on new airplane designs. Any
resulting intercycle, residual, or runback ice has to be accounted for
when showing compliance with the subpart B regulations in icing. No
changes are made as a result of this comment.
4. Subpart C--Structures
a. Structural Design Envelope (Proposed Sec.  23.300/Now Sec.  23.2200)
    In the NPRM, proposed Sec.  23.300 (now Sec.  23.2200) would have
required the applicant to determine the structural design envelope,
which describes the range and limits of airplane design and operational
parameters for which the applicant would show compliance with the
requirements of subpart C. Proposed Sec.  23.300 would have required
the applicant to account for all airplane design and operational
parameters that affect structural loads, strength, durability, and
aeroelasticity, including structural design airspeeds and Mach numbers.
    Several commenters identified concerns with the detailed
definitions of airspeeds for which applicants would be required to
account. They pointed out that, for some types of airplanes, these
airspeeds may not be appropriate in particular circumstances. EASA
recommended removal of the speed definitions for a more generic
proposal in its proposed CS 23.320.
    The FAA recognizes the commenters' concerns on the various issues
in proposed Sec.  23.300(a). The FAA believes the best way to address
these comments is to adopt regulatory text similar to the text in
EASA's section CS 23.320, which removes the need to define individual
design airspeeds in the regulation. Some comments on proposed Sec.
23.300(a) recommended retaining certain methods of compliance language,
such as defining VC in terms of VH, which is in
former part 23. In keeping with the intent of this rulemaking, however,
the FAA believes these types of prescriptive standards are best moved
to means of compliance.
    Air Tractor commented on proposed Sec.  23.300(b), which addressed
design maneuvering load factors for the structural design envelope. Air
Tractor raised concerns that obtaining consensus compliance from the
FAA without the prescriptive formula established by former Sec.
23.337(a) would be a protracted battle--worse than the existing issue
paper process for non-standard design.
    Regarding Air Tractor's concerns, the FAA has decided to move the
prescriptive formula for determining the design maneuvering load
factors to means of compliance. The FAA also reiterates that the phrase
``service history'' is intended to mean the design maneuvering load
factors should be based on those load factors used for airplanes with
successful service histories that have similar design, operational
capabilities, and intended use. If there are no existing similar
designs, the FAA will work with the applicant to identify the most
appropriate means of compliance. In general, the FAA does not expect
applicants to measure and record maneuvering load factors on new
designs.
    EASA asserted that the language in proposed Sec.  23.300(c) was too
design specific and could be replaced with the text from its proposed
CS 23.305.
    The FAA finds that proposed Sec.  23.300(c) is not overly design
specific, because each of the enumerated items must be taken into
account, regardless of the applicant's design. The FAA therefore adopts
paragraph (c) as proposed.
    Air Tractor recommended the FAA change ``empty weight to the
maximum weight'' to ``minimum flying weight to maximum weight,'' in
proposed Sec.  23.300(c)(1). Air Tractor stated this language applies
to all airplanes and is appropriate for certification; while ``empty
weight'' applies only to certain airplanes' operational requirements.
    The FAA notes Air Tractor's recommendation that ``empty weight'' in
Sec.  23.2200(c)(1) should be replaced with ``minimum flying weight.''
However, the FAA believes that establishing a design empty weight is
necessary so that variations in the mass of properties such as fuel,
payloads, and occupants, when added to the airplane, can be accounted
for.
    The Associations recommended deleting the term ``All'' from the
beginning of proposed Sec.  23.300(c)(1) and (e) for simplification.
Textron recommended changing ``All'' in proposed Sec.  23.300(c)(1) to
``Each.'' Textron stated the change would be consistent with former
part 23, which uses ``each weight'' throughout the subparts, whereas
``all'' implies an applicant would have to evaluate an infinite number
of weights rather than those that are relevant. Textron also
recommended replacing ``All'' in proposed Sec.  23.300(e) with ``Each
critical altitude,'' because ``all'' is too encompassing.
    The FAA agrees with the recommendation to replace ``All'' with
``Each'' in proposed Sec.  23.300(c) and (e) and revises the language
in both paragraphs accordingly. The FAA also adds the word ``critical''
so the subsection text reads ``Each critical. . .''. In this context,
``critical'' refers to a weight or altitude that results in a maximum
or minimum structural loading condition. A ``critical weight'' will,
for example, be the weight of the airplane at its highest possible
value with no fuel in the wing. This condition will reduce the effects
of inertia in the wing and result in maximum structural loads. A
``critical altitude'' will be the altitude where the maximum pressure
differential occurs in a pressurized cabin, or an altitude where the
effects of atmospheric compressibility cause changes to the airplane
aerodynamic coefficients, resulting in maximum structural loads.
    EASA commented that proposed Sec.  23.300(d) was too design
specific and should cover loads resulting from controls.
    The FAA interprets EASA's comment to mean the FAA should consider
non-traditional methods of control, such as vectored thrust. The FAA
agrees and revises paragraph (d) to include non-traditional control
systems.
    EASA also commented on proposed Sec.  23.300(e), stating it would
create a requirement that is not applicable to very-light aircraft
(VLA) today. EASA asserted that the intent can be covered by the new
proposal for flight loads in proposed Sec.  23.310 (now Sec.  23.2210).
    While the FAA notes EASA's concern with proposed Sec.  23.300(e),
the FAA finds that paragraph (e), as proposed, would place only an
insignificant burden on an applicant using the VLA standard. The FAA
finds a simple method of compliance, such as for a maximum altitude of
14,000 feet, could be incorporated into an industry consensus standard
to meet this requirement.
b. Interaction of Systems and Structures (Proposed Sec.  23.305/Now
Sec.  23.2205)
    In the NPRM, proposed Sec.  23.305 (now Sec.  23.2205) would have
provided a regulatory framework for the evaluation of systems intended
to modify an airplane's structural design envelope or structural
performance, and other systems whose normal operating state or failed
states may affect structural performance. Compliance with proposed
Sec.  23.305 would have provided acceptable mitigation of structural

hazards identified in the functional hazard assessments required by
proposed Sec.  23.1315.
    Textron recommended removing proposed Sec.  23.305 because the NPRM
makes clear that, with or without proposed Sec.  23.305, the safety
intent of proposed Sec.  23.1315 covers the interaction of systems and
structures. Textron also objected to the use of, or reference to, non-
part 23 data. As an example, Textron cited the reference in the
preamble to FAA special condition number 25-390-SC,\30\ which the FAA
said would be an acceptable means of compliance with proposed Sec.
23.305. Textron questioned whether there was justification for this
requirement if part 23 data was not available.
---------------------------------------------------------------------------

    \30\ http://rgl.faa.gov/Regulatory_and_Guidance_Library/rgSC.nsf/MainFrame?OpenFrameset.
---------------------------------------------------------------------------

    In response to Textron's comment regarding the necessity of
proposed Sec.  23.305, the FAA notes the intent stated in the NPRM was
erroneous in its description of the relationship between proposed Sec.
23.305 and proposed Sec.  23.1315 (now Sec.  23.2510). The correct
intent of proposed Sec.  23.305 is to provide a requirement for those
systems intended to directly affect structural performance. An example
of this type of system is a structural load alleviation system. Former
Sec.  23.1309 and Sec.  23.2510 do not envision these types of systems
and the FAA has previously issued special conditions to address these
unique and novel systems. Therefore, the FAA retains proposed Sec.
23.305 as Sec.  23.2205 in this final rule because it provides a way
for applicants to address failures in systems intended to directly
affect structural performance by accounting for the probability of such
failures and the likely pilot reactions to them.
    Also, regarding Textron's comment that the NPRM preamble referenced
a part 25 special condition that did not contain part 23 data, the FAA
notes the reference was used as an example because the wording of the
special condition was typical of others relating to Interaction of
Systems and Structure, which establish an acceptable method of
compliance with this section. The FAA has issued a part 23 special
condition (23-258A-SC).\31\ However, the FAA did not use the part 23
special condition as an example because, while it is an acceptable
method of compliance with this section, the approach used in it is not
typical of other special conditions addressing these issues.
---------------------------------------------------------------------------

    \31\ 78 FR 10055, February 13, 2013.
---------------------------------------------------------------------------

    Textron also stated the phrase ``affect structural performance''
was too vague and should be better defined for clarity. Textron noted
every trim system, flight control system, and high lift system affects
structural performance at some level. Textron recommended either
eliminating this phrase or using the preamble to define ``structural
performance.'' Textron recommended proposed Sec.  23.305 be revised to
provide that, for airplanes equipped with systems intended to alleviate
the impact of the requirements of this subpart and affect the
structural design envelope, either directly or as a result of failure
or malfunction, the applicant must account for the influence and
failure conditions of these systems when showing compliance with the
requirements of this subpart.
    The Associations commented that proposed Sec.  23.305 was intended
to address systems, which may use aerodynamic or other means to
alleviate loads in certain conditions and to ensure structural
integrity remains in the event these systems were to fail. The
commenters requested the FAA change the language to ensure the intent
of this section is clear and there are no unintended consequences, such
as creating a requirement to perform systems safety assessments on all
systems and structure interactions. The commenters asserted that this
would create a tremendous burden with no measurable benefit. The
commenters proposed Sec.  23.305 be revised to provide that, for
airplanes equipped with systems that are intended to alleviate
structural loads, the applicant must account for the influence and
failure conditions of these systems when showing compliance with the
requirements of this subpart.
    The FAA agrees with Textron and the Associations that Sec.  23.2205
should address only those systems intended to affect structural
performance. In the NPRM, the FAA referred to these types of systems as
``structural systems''. The FAA referred to other types of systems as
``non-structural systems''. The FAA agrees that these non-structural
systems are adequately addressed by Sec.  23.2510. The FAA is using the
NPRM description of structural systems in rewording Sec.  23.2205 to
ensure that any airplane equipped with a system intended to affect
structural performance would be provided the same level of safety as an
airplane not equipped with such a system.
c. Structural Design Loads (Proposed Sec.  23.310/Now Sec.  23.2210)
    In the NPRM, proposed Sec.  23.310 (now Sec.  23.2210) would have
required--
     An applicant to determine structural design loads
resulting from an externally or internally applied pressure, force, or
moment that may occur in flight, ground and water operations, ground
and water handling, and while the airplane is parked or moored.
     An applicant to determine structural design loads at all
combinations of parameters on and within the boundaries of the
structural design envelope that would result in the most severe loading
conditions; and
     The magnitude and distribution of these loads be based on
physical principles and be no less than service history has shown can
occur within the structural design envelope.
    The Associations recommended adding the phrase ``as applicable'' to
proposed Sec.  23.310(a) to address the varying bases to determine load
calculations. These commenters also recommended replacing the term
``any'' with the word ``likely,'' because the calculation of any
externally or internally applied pressure, force, or moment would
result in boundless design and calculation. Textron recommended the
same revisions. Textron noted that the rule implies that all airplanes
will be required to determine both ground and water loads, but not all
airplanes are amphibious.
    The FAA agrees with Textron and the Associations concerning the
comments on adding the phrase ``as applicable'' and removing the word
``any'' in proposed Sec.  23.310(a). The FAA also agrees with limiting
the scope of proposed Sec.  23.310(a) by adding the word ``likely'' to
the description of the loading conditions the applicant must consider.
As explained in the discussion of proposed Sec.  23.205, ``likely''
means reasonably expected based on the conditions that may exist.
Accordingly, the FAA revises Sec.  23.2210(a) to capture these changes.
    Air Tractor recommended the FAA delete the ``service history''
clause from proposed Sec.  23.310(c) because there is no ``service
history'' for most new airplanes and there is danger that the FAA will
require that service history be collected before certification is
granted for a new design. EASA also noted that a ``service history''
will not always be available for innovative designs.
    The FAA partially agrees with Air Tractor regarding the meaning of
``service history'' in proposed Sec.  23.310(c). Service history, in
this sense, refers to the service history and experience gained
throughout aviation history. In Air Tractor's case, service history
would be the service history of other restricted category agricultural
airplanes of similar design. The FAA finds Sec.  23.2200(b) adequately
covers the intent of the ``service history''

requirement and therefore removes it from Sec.  23.2210(c).
d. Flight Load Conditions (Proposed Sec.  23.315/Now Sec.  23.2215)
    In the NPRM, proposed Sec.  23.315 (now Sec.  23.2215) would have
required an applicant to determine the loads resulting from vertical
and horizontal atmospheric gusts, symmetric and asymmetric maneuvers,
and, for multiengine airplanes, failure of the powerplant unit which
results in the most severe structural loads.
    EASA noted the proposed rule did not cover the objective that loads
should be considered for the operational envelope, but instead based
the requirement on measured gust statistics. EASA proposed using its CS
23.315 language because it is more objective and does not include
design details.
    The FAA finds the requirement to consider loads throughout the
operational envelope is addressed by proposed Sec.  23.310(b) (now
Sec.  23.2210(a)(2)). However, the FAA agrees with EASA's comment that
the proposed rule language is too design specific. Therefore, FAA
revises the rule language to remove design specifics. In particular,
the FAA removes proposed Sec.  23.215(c), which addressed canted
lifting surfaces. The FAA finds Sec.  23.2210(c) adequately addresses
this requirement. The FAA also changes the wording of proposed Sec.
23.215(d) (now 23.2215(c)) to account for the possibility that a single
powerplant, operating two separate propellers, could develop asymmetric
thrust if one propeller system experienced a failure. This would result
in a condition similar to an engine failure in a multiengine airplane,
described in the former regulations. Although no applicant has
submitted such a design for approval to date, given the increased
flexibility this rule provides, future applicants may propose such a
design. In that case, this design will be subject to the same safety
concern and the same need to address it, as applicants for approval of
multiengine airplanes.
    Air Tractor commented on proposed Sec.  23.315(a) and questioned
whether the gust velocities in former part 23 or CAR 3 were based on
``measured gust statistics.'' Air Tractor noted it has never seen a
technical report to that effect. Air Tractor also questioned whether
the FAA would deem the CAR 3 and current part 23 values sufficient, and
raised concerns that making up its own requirements to meet FAA
approval would be difficult.
    The FAA changed the gust load formula in former Sec.  23.341,
amendment 23-7 \32\ to incorporate the mass parameter approach to
calculating gust loads. The mass parameter approach was developed and
calibrated against measured gust data on transport category airplanes.
The FAA does not intend for applicants for a new TC to measure gust
loadings. The former gust formula remains an acceptable method of
compliance with this regulation. The FAA developed this regulation so
certain airplanes could take advantage of alternate analysis methods,
including the power spectral density approach. Examples of these types
of airplanes include high altitude and endurance airplanes, where
dynamic response of the airplane structure must be considered in the
gust load analysis.
---------------------------------------------------------------------------

    \32\ 34 FR 13078, August 13, 1969.
---------------------------------------------------------------------------

e. Ground and Water Load Conditions (Proposed Sec.  23.320/Now Sec.
23.2220)
    In the NPRM, proposed Sec.  23.320 (now Sec.  23.2220) would have
required an applicant to determine the loads resulting from taxi, take-
off, landing, and ground handling conditions occurring in normal and
adverse attitudes and configurations.
    EASA proposed using its A-NPA CS 23.325 language because it is more
objective and covers more situations, such as landing on snow or other
surfaces not covered in proposed Sec.  23.320. BendixKing asked that
the FAA delete ``sea,'' stating the word is neither required nor
accurate.
    The FAA agrees with EASA's comments and revises the text in Sec.
23.2220 to include all operating surfaces, which includes, at a
minimum, snow or ice covered land and water. EASA referred to snow and
other surfaces not covered in the proposed text, presumably meaning
EASA does not consider operations on ``snow or other surfaces'' to be
operations on the ground. While the FAA is using EASA's CS A-NPA 23.325
language, the FAA finds EASA's language citing weight and velocity to
be unnecessary. These parameters are addressed in Sec.  23.2200.
    Air Tractor asked whether the ``ground handling conditions'' in
proposed Sec.  23.320(a) would be different from the ``jacking and
towing conditions'' in proposed Sec.  23.320(c). If so, the commenter
asked what ``ground handling conditions'' meant. Air Tractor also asked
whether this dealt with protection from ``hangar rash.'' Finally, Air
Tractor sought clarification on whether it would now need to define the
structural loads associated with docking an airplane, or from wave
motion causing scuffing when a seaplane is moored against a dock.
    The FAA notes the ``ground handling conditions'' referenced in
proposed Sec.  23.320(a) (now Sec.  23.2220) are different than the
``jacking and towing conditions'' referenced in Sec.  23.320(c) (now
Sec.  23.2220). The reference to ``handling conditions'' is intended to
cover both ground handling conditions and jacking and towing
conditions. The FAA revises Sec.  23.2220 to cover ``taxi, takeoff,
landing, and handling conditions.''
f. Component Loading Conditions (Proposed Sec.  23.325/Now Sec.
23.2225)
    In the NPRM, proposed Sec.  23.325 (now Sec.  23.2225) would have
required an applicant to determine the loads acting on each engine
mount, flight control, high lift surface, and the loads acting on
pressurized cabins.
    EASA commented that proposed Sec.  23.325(b) covered the loads on
components subject to earlier defined loads in proposed Sec. Sec.
23.305 through 23.320. EASA recommended the FAA simplify the
requirement to avoid different interpretations by reflecting the
relation to the previous requirements as follows:

 Interaction of systems and structures
 Structural design loads
 Flight Load Conditions
 Ground and water load conditions

    The FAA finds that a separate rule for component loading conditions
is necessary to address structural loading conditions that do not fall
under the requirements for flight and ground loads. Examples of these
loading conditions include control surface jamming and pressurized
cabin loads. The FAA revises Sec.  23.2225 to clarify the types of
loads applicants must account for.
    Textron and the Associations asked the FAA to revise the ``relief
valve'' language in proposed Sec.  23.325(c), which was a design-
specific solution, in favor of more performance-based language. Textron
suggested language such as ``from zero to the maximum relief pressure
combined with gust and maneuver loads.'' The Associations recommended
replacing ``valve'' with ``pressure.''
    The FAA agrees with Textron and the Associations on the use of the
term ``relief valve.'' The FAA revises Sec.  23.2225(c)(1), (2), and
(3) by replacing the term ``relief valve'' with ``relief pressure.''
    The FAA agrees with a comment made at the public meeting by the
Associations that proposed Sec.  23.325 should cover sudden engine
stoppage loads for turbine engines, as did former part 23. A
requirement for the design of

engine mounts for turbine engines to be able to withstand a sudden
engine stoppage has been in former part 23 since 1980.\33\ Former Sec.
23.361(b)(1) required, in pertinent part, that for turbine engine
installations, the engine mounts and supporting structure be designed
to withstand an engine torque load imposed by a sudden engine stoppage.
The requirement applied only to turbine engines because reciprocating
engines typically do not have significant rotational moments of
inertia. As in former part 23, reciprocating powerplants, with their
lower moments of inertia, are not included in this section of the rule.
The requirement applies only to turbines and other types of powerplants
that have significant rotational moments of inertia created by rotating
powerplant components (e.g., electric motor powerplants). Therefore,
the FAA adds protection of powerplant mounts and supporting structure
from sudden powerplant stoppage for all non-reciprocating powerplants
to Sec.  23.2225(a)(2). This change is consistent with the goal of
capturing the safety intent of former part 23, including Sec.  23.361,
as stated in the NPRM preamble, and with the performance-based nature
of this rule and its goal of more easily accommodating future designs
and technologies.
---------------------------------------------------------------------------

    \33\ 45 FR 60171, September 11, 1980.
---------------------------------------------------------------------------

    Finally, the FAA revises Sec.  23.2225(b) to clarify the gust loads
that must be accounted for and the meaning of ``ground operations,''
making this section consistent with the changes discussed previously
for Sec.  23.2220.
g. Limit and Ultimate Loads (Proposed Sec.  23.330/Now Sec.  23.2230)
    In the NPRM, proposed Sec.  23.330 (now Sec.  23.2230) would have
described how the applicant must determine the limit and ultimate loads
associated with the structural design loads. Proposed Sec.  23.330
retained the current 1.5 safety factor for ultimate loads.
    The Associations recommended the FAA revise proposed Sec.  23.330
by deleting the phrase ``special or other factors of safety are
necessary to meet the requirements of'' and replacing it with
``ultimate loads are specified in.'' These commenters noted the
section, as written, would not require the establishment of limit loads
if a special factor of safety is used to meet the requirement. Textron
recommended the same revision, explaining that proposed Sec.  23.330
need not address ``special or other factors of safety,'' other than in
some cases when an ultimate load is specified, because proposed Sec.
23.515(c) specified that limit and ultimate loads are multiplied by
special factors of safety.
    The FAA agrees with the comments regarding cases where loads are
expressed only as ultimate loads. The FAA deletes the introductory
phrase ``unless special or other factors of safety are necessary to
meet the requirements of this subpart,'' in proposed Sec.  23.330. The
FAA notes Sec.  23.2265(c) specifies that limit and ultimate loads are
multiplied by special factors of safety. Furthermore, the FAA revises
Sec.  23.2230 by inserting the phrase ``unless otherwise specified
elsewhere in this part,'' which captures the intent of former Sec.
23.303.
    EASA recommended the FAA should also address the former requirement
for redistribution of loads due to deflections under loads. EASA also
recommended the regulation cover the specific case where strength
specifications are expressed only in ultimate loads and permanent
deformation is accepted.
    The FAA notes Sec.  23.2210(b) addresses the issue of
redistribution of loads. Specifically, 23.2210(b) requires the
distribution of loads be based on physical principles. The FAA finds
redistribution of load due to deflection is an expression of physical
principles and is retaining this requirement in Sec.  23.2210(b) of
this rule.
    An individual commenter asked the FAA to remove the ``arbitrarily
prescriptive'' 1.5 factor of safety and substitute a more performance-
based approach. The commenter explained that advances in probabilistic
analysis have increased understanding of actual variables like load
predictions, material properties, and airplane operations. The
commenter proposed defining the value for structural failure more
explicitly and allowing the applicant to account for the variations to
achieve the value, allowing for more efficient designs. The commenter
suggested retaining the 1.5 factor of safety as a possible approval
approach to establish the means of compliance.
    The FAA notes the 1.5 factor of safety has been used for many years
and has provided an acceptable level of safety. Probabilistic analysis
methods and the data necessary to support them are not sufficiently
mature to provide the same level of assurance of safety. As
probabilistic methods mature, the FAA will consider their use if
applicants can show they provide an equivalent level of safety.
h. Structural Strength (Proposed Sec.  23.400/Now Sec.  23.2235)
    In the NPRM, proposed Sec.  23.400 (now Sec.  23.2235) would have
required an applicant to demonstrate the structure will support limit
and ultimate loads. The NPRM explained that in this context,
``demonstrate'' means the applicant must conduct structural tests to
show compliance with the structural performance requirements unless the
applicant shows that a structural analysis is reliable and applicable
to the structure.
    The Associations recommended adding ``unsafe'' at the beginning of
proposed Sec.  23.400(a)(1) to clarify the intent of the requirement
and ensure it is not viewed as including expected or non-critical types
of interference, such as thrust reverser buckets making normal contact
with each other. Similarly, Textron recommended inserting the word
``safe'' before ``operation'' in proposed paragraph (a)(1) to ensure
that ``interference'' in the regulation will always be interpreted to
mean interference that would cause an unsafe condition.
    The FAA agrees that inserting the word ``safe'' in the text of
proposed Sec.  23.400(a)(1) will clarify that the structure must
support limit loads without interference with the ``safe'' operation of
the airplane. This suggested change is consistent with the
corresponding requirements in former part 23, and will resolve the
Associations' concern as well. Accordingly, the FAA revises Sec.
23.2235(a)(1) to capture this change.
    NJASAP asked why the FAA proposed removing time requirements (the
capability of the airplane structure to support ultimate loads without
failure for at least three seconds) in proposed Sec.  23.400.
    As discussed in the NPRM preamble, the FAA considers the ``3-
second'' rule a statement of physical principles and sound testing
practices that does not need to be stated in the requirements for
structural strength. It is more appropriate for inclusion in a means of
compliance. The FAA makes no change to the regulatory text based on
NJASAP's comment.
i. Structural Durability (Proposed Sec.  23.405/Now Sec.  23.2240)
    In the NPRM, proposed Sec.  23.405 (now Sec.  23.2240) would have
required an applicant to develop and implement procedures to prevent
structural failures due to foreseeable causes of strength degradation,
and to prevent rapid decompression in airplanes with a maximum
operating altitude greater than 41,000 feet. Proposed Sec.  23.405
would have also required an airplane to be capable of continued safe
flight and landing with foreseeable structural damage caused by high-
energy

fragments from an uncontained engine or rotating machinery failure.
    The Associations said proposed Sec.  23.405 remains ``far too
prescriptive and design oriented.'' The commenters recommended language
that they believed addresses the objectives of the rule without being
so design focused. Specifically the Associations suggested the phrase
``serious or fatal injuries, loss of the airplane, or extended periods
of operation with reduced safety margins'' in Sec.  23.2240(a) be
replaced with ``unsafe conditions.''
    Textron suggested that the proposed rule is too prescriptive
regarding the number of compartments for compartment floor
depressurization, as well as in prescribing the ``design'' structure
rather than specifying the required capability of the structure.
Textron suggested revising proposed Sec.  23.405 similar to that
suggested by the Associations.
    An individual commenter recommended the FAA delete the phrase
``loss of the airplane'' from proposed Sec.  23.405(a). The commenter
stated this would address the long-understood interpretation that part
23 does not include certain structures for required evaluation on the
effects of fatigue failure, such as landing gear and engine support (or
hull loss, as discussed in the NPRM preamble). Without this revision,
the commenter noted the intent of the rule not to increase the burden
on certification would be nullified. In effect, the commenter found the
proposed rule would require the same structure as is currently
evaluated in part 25, which is inconsistent with former part 23. The
commenter favored incorporating a comprehensive fatigue evaluation of
structure as is currently in part 25.
    The FAA agrees with the suggestion to delete the phrase ``loss of
the airplane'' in paragraph (a). The FAA finds the prevention of
serious or fatal injuries and the prevention of extended periods of
operation with reduced safety margins is the objective of Sec.
23.2240. The FAA will not adopt the Associations' recommended change to
replace the phrase ``serious or fatal injuries, loss of the airplane,
or extended periods of operation with reduced safety margins'' with
``unsafe conditions.'' The term ``unsafe condition'' is the threshold
for the FAA issuing airworthiness directives under 14 CFR part 39, and
is not an accurate term to be used in this section.
    The FAA also revises paragraph (a) to reflect more completely the
requirements of the former part 23 regulations this section is
replacing.\34\ Because proposed Sec.  23.405(a) did not refer
specifically to the Airworthiness Limitations section (ALS) of the
Instructions for Continued Airworthiness (ICA) (as did former Sec.
23.575), it could be interpreted as allowing the procedures to be
placed in another part of the ICA. Therefore, the FAA revises the text
in paragraph (a) to clarify that these procedures must be in the ALS.
The FAA also clarifies that ``inspections'' developed under this
section must be included in the ALS in addition to the ``procedures''
developed under the section, because former Sec.  23.575 required both
to be in the ALS. Appendix G to former part 23, now appendix A to this
final rule, requires the FAA to approve the ALS. Finally, the FAA notes
that compliance with the ALS is mandatory under Sec. Sec.  43.16 and
91.403(c).
---------------------------------------------------------------------------

    \34\ Sec. Sec.  23.365(e), Pressurized cabin loads; 23.571,
Metallic pressurized cabin structures; 23.572, Metallic wing,
empennage, and associated structures; 23.573, Damage tolerance and
fatigue evaluation of structure; 23.574, Metallic damage tolerance
and fatigue evaluation of commuter category airplanes; 23.575,
Inspections and other procedures; and 23.627, Fatigue strength. (81
FR 13476, March 14, 2016).
---------------------------------------------------------------------------

    EASA suggested replacing the design-specific requirements in
proposed Sec.  23.405(b) with more objective requirements from EASA's
CS 23.340(b) to allow proportionality for different airplane levels. In
particular, EASA said more objective requirements should replace the
proposed requirements related to pressurized airplanes and uncontained
engine failure.
    The FAA notes the language in EASA's proposed CS 23.340 could be
interpreted as expanding the scope of the former regulations by
requiring evaluation of discrete source damage for all airplanes
certificated under part 23. As stated in the NPRM, the FAA intended
proposed Sec.  23.405(b) and (c) to capture the intent of former
Sec. Sec.  23.365(e) and 23.571(d), which only addressed airplanes with
pressurized compartments. Sudden release of pressure and operating
above 41,000 feet altitude present the same hazards to the airplane
occupants regardless of airplane category or size.
    The FAA moves the content of proposed Sec.  23.405(b) and (c) to
Sec.  23.2240(c)(1) and (c)(2) in the final rule. The final rule also
adds new Sec.  23.2240(b), which addresses the requirement for level 4
airplanes. This requirement is similar to the former Sec.  23.574
requirement for damage tolerance evaluations of commuter category
airplanes. The FAA inadvertently left this requirement out of the NPRM.
    The FAA agrees with the comments that proposed Sec.  23.405(b) was
overly prescriptive. The FAA deletes the detailed description of the
pressurized compartment and emphasizes the sudden release of pressure
in Sec.  23.2240(c)(1) and (c)(2). The FAA retains reference to door
and window failures as examples of the types of failures that could
result in sudden release of pressure.
    EASA stated that proposed Sec.  23.405(d) is too specific to engine
rotorburst; however, other risks could be expected from new
technologies that should also be considered.
    The FAA agrees with EASA's comment that paragraph (d) should
address all high-energy fragments, not just fragments from an engine
rotorburst. The FAA revises Sec.  23.2240(d) to include all high-energy
fragments. The FAA also includes turbine engines and rotating machinery
as sources of high-energy fragments.
    Several other commenters also commented on proposed Sec.
23.405(d), noting that former part 23 required ``minimizing'' hazards
associated with damage from uncontained engine or rotating machinery
failures, but the NPRM would require the airplane be able to ``continue
safe flight and landing'' following such damage. The commenters
asserted that there is no way to eliminate all the risks that will
prevent the ``continued safe flight and landing,'' and asked the FAA
maintain the requirement to ``minimize'' these hazards as in former
Sec.  23.903(b)(1).
    The FAA agrees that proposed Sec.  23.405(d) is inconsistent with
the description in the NPRM preamble. Therefore, the FAA agrees with
the commenters' recommendation to adopt the term ``minimize'' in Sec.
23.2240(d). The FAA does not intend for applicants to incorporate all
possible design precautions against rotorburst hazards, especially
those that are resource prohibitive or have a negligible impact on
safety. The FAA expects an applicant's compliance with Sec.  23.2240(d)
to incorporate all practical design precautions to minimize the hazards
due to high-energy fragments.
j. Aeroelasticity (Proposed Sec.  23.410/Now Sec.  23.2245)
    In the NPRM, proposed Sec.  23.410 (now Sec.  23.2245) would have
required an airplane to be free from flutter, control reversal, and
divergence at all speeds within and sufficiently beyond the structural
design envelope, for any configuration and condition of operation,
accounting for critical

degrees of freedom, and any critical failures or malfunctions. Proposed
Sec.  23.410 would have also required an applicant to establish
tolerances for all quantities that affect flutter.
    Air Tractor and Transport Canada raised concerns about the phrase
``sufficiently beyond the structural design envelope'' in proposed
Sec.  23.410(a)(1). Transport Canada said the wording is subjective and
does not convey a performance requirement and suggested complementing
the phrase ``sufficiently beyond'' with safety objective requirements.
Air Tractor noted the existing regulations do not extend beyond the
design envelope. Air Tractor asked for clarification on what is
considered ``sufficiently beyond.''
    Regarding Air Tractor's assertion that the former regulations did
not extend beyond the design envelope, the FAA intended proposed Sec.
23.410 to capture the safety intent of former Sec. Sec.  23.629,
23.677, and 23.687 without introducing the inflexibility created by the
former regulations. Former Sec.  23.629(c) required that flutter
analysis show freedom from flutter, control reversal, and divergence up
to 20 percent above dive speed. Existing part 25 rule language requires
flutter analysis to show this up to 15 percent above dive speed. This
is to account for uncertainties inherent in analytical techniques. Part
25 requires a smaller margin above dive speed due to its more rigorous
analytical requirements. Additionally, former Sec.  23.629(b)(4)
precluded any large or rapid reduction in damping as dive speed is
approached in flight tests.
    As for Air Tractor's comment requesting clarification on what is
considered ``sufficiently beyond'' in proposed Sec.  23.410(a)(1), the
former part 23 requirements for margins on analyses and flight tests
worked together to ensure a momentary inadvertent excursion above dive
speed in operation, or combined variations in quantities that may
affect flutter, did not result in a catastrophic flutter event. Thus,
the FAA required a sufficient margin above dive speed in former part 23
for many years. The phrase ``sufficiently beyond the structural design
envelope'' is intended to require a sufficient margin consistent with
the requirements of former part 23. However, as technology and
analytical techniques evolve and improve, the new language will allow
room for the methods of compliance to adapt and possibly change the
appropriate margin needed for safe operations. This language is also
harmonized with EASA's proposed rule language.
    Several commenters raised concerns about the use of the term
``any'' in proposed Sec.  23.410(a). The Associations asked the FAA to
revise proposed Sec.  23.410(a)(2) to require the airplane to be free
from flutter, control reversal, and divergence for ``approved''
configurations and conditions of operation, rather than for ``any''
configuration and condition of operation. Textron recommended the FAA
require the airplane to be free from flutter, control reversal, and
divergence for ``any likely'' configuration and condition of operation.
Similarly, the Associations suggested removing the term ``any'' from
proposed Sec.  23.410(a)(4).
    The FAA notes the commenters concerns about the term ``any'' in
Sec.  23.2245(a)(2) and (a)(4). In the NPRM, the FAA explained that
Sec.  23.2245 would capture the safety intent of former Sec.  23.629.
Former Sec.  23.629(a) has required the airplane to be free from
flutter, control reversal, and divergence for ``any condition of
operation'' since 1978. This terminology originated from CAR 3.311, the
predecessor to former Sec.  23.629, was adopted in 1947 and required
the wings, tail, and control surfaces to be free from flutter,
divergence, and control reversal for ``all conditions of operation.''
The FAA recognizes it is impossible to evaluate an infinite number of
data points, but that is not the intent of Sec.  23.2245 nor was it the
intent of its predecessor regulations. Rather, the FAA interprets the
term ``any'' in Sec.  23.2245(a)(2) as requiring the applicant to
exercise due diligence by accounting for a sufficient number of data
points that would enable the applicant to state the entire envelope has
been evaluated and is safe. This interpretation is consistent with the
way the FAA has interpreted CAR 3.311 and former Sec.  23.629. Because
the FAA has used the terms ``any'' and ``all'' in its flutter
requirements for decades, the FAA is retaining the term ``any'' in
Sec.  23.2245(a)(2) and (a)(4). This maintains harmonization with
EASA's proposed rule language.
    Several commenters raised concerns with terminology in proposed
Sec.  23.410(b). Textron and the Associations suggested the FAA require
the applicant to establish and account for ``sensitivities'' rather
than ``tolerances'' because the term ``tolerances'' has a very specific
meaning and a proper flutter analysis is a collection of flutter
sensitivity analyses.\35\ The Astronautics Corporation of America
(Astronautics) sought clarification of the term ``quantities'' in
proposed Sec.  23.410(b) and offered alternative regulatory language in
an attempt to clarify its meaning. Textron proposed replacing
``quantities'' with ``parameters.''
---------------------------------------------------------------------------

    \35\ Textron specifically noted that proposed Sec.  23.2245(b)
``would require the applicant to specify a +/-X% tolerance on things
such as cross sectional properties (torsional GJ), cross sectional
moments of inertia, or other qualities that affect flutter but
aren't intended to have a +/-X% tolerance.''
---------------------------------------------------------------------------

    Regarding Textron, the Associations and Astronautics' comments on
the use of ``tolerances'' and ``quantities'' in proposed Sec.
23.410(b), the FAA is retaining the terms ``tolerances'' and
``quantities'' in Sec.  23.2245(b). The FAA intends Sec.  23.2245 to
capture the safety intent of former Sec.  23.629, which has contained
the terms ``tolerances'' and ``quantities'' since 1978.\36\ The FAA has
interpreted them consistently from that time, and will continue to do
so in Sec.  23.2245. This language is also harmonized with EASA's
proposed rule language.
---------------------------------------------------------------------------

    \36\ See 43 FR 50592, October 30, 1978.
---------------------------------------------------------------------------

    Textron recommended removing the word ``establish'' from the
proposed language. The commenter noted that you cannot account for
something without establishing it first.
    The FAA agrees with Textron that it would be redundant to require
an applicant to establish and account for tolerances. For that reason,
the FAA retains the word ``establish'' and deletes the words ``and
account for'' from Sec.  23.2245(b) in the final rule. This change
emphasizes the necessity of fully analyzing these tolerances and
harmonizes with EASA's proposed rule language.
k. Design and Construction Principles (Proposed Sec.  23.500/Now Sec.
23.2250)
    In the NPRM, proposed Sec.  23.500 (now Sec.  23.2250) would have
required--
     An applicant to design each part, article, and assembly
for the expected operating conditions of the airplane;
     The design data to adequately define the part, article, or
assembly configuration, its design features, and any materials and
processes used;
     An applicant to determine the suitability of each design
detail and part having an important bearing on safety in operations;
and
     The control system to be free from jamming, excessive
friction, and excessive deflection when the control system and its
supporting structure are subjected to loads corresponding to the limit
airloads when the primary controls are subjected to the lesser of the
limit airloads or limit pilot forces, and when the secondary controls
are subjected to loads not less than those corresponding to maximum
pilot effort.

    The Associations recommended the FAA change the title of proposed
Sec.  23.500 from ``Structural design'' to ``Design and construction
principles.''
    The FAA concurs with the recommendation by the Associations to
change the title of Sec.  23.2250 to ``Design and construction
principles.'' The FAA agrees the suggested title is a better descriptor
and will harmonize with EASA's proposed title for this section, and
adopts it for this rule.
    Several comments addressed proposed Sec.  23.500(d). Air Tractor
recommended that the FAA revise the wording of proposed Sec.  23.500(d)
to specify that it applies to flight controls. Air Tractor further
noted that it appears that the definition of ``maximum pilot effort''
has been untethered from former Sec. Sec.  23.397(b) and 23.143(c),
making it necessary for every applicant ``to re-invent the wheel.''
    Regarding Air Tractor's comment proposing to add the term
``flight'' to further define ``control system'', the term ``control
system'' has been used consistently for many years in this context in
the former regulations, and is understood to refer to ``flight''
controls. This text also harmonizes with EASA's proposed rule language.
Therefore, the FAA adopts the language as proposed in the NPRM.
    As for Air Tractor's concern that maximum pilot effort has been
untethered from former Sec. Sec.  23.397(b) and 23.143(c), the FAA
notes that under the new performance-based regulations, applicants will
be free to use former part 23 or other accepted means, such as industry
consensus standards, as a means of compliance. These accepted means of
compliance will detail how the airplane will meet the performance-based
requirements.
    The Associations stated that it is appropriate for means of
compliance to specify how airframe and control system interactions will
be tested up to limit loads and that, depending on the nature of the
control system, it may be more or less appropriate to perform such a
test. These tests ensure the appropriate level of testing is always
applied to traditional flight controls and also to future systems,
which may include fans or thrusters. The commenters suggested the level
of detail be contained in accepted standards. Additionally, the
commenters recommended the FAA consider revising proposed Sec.
23.500(d) by deleting paragraphs (1), (2), and (3) and adding the
phrase ``the airplane is subjected to expected limit airloads'' to the
end of paragraph (d). EASA also recommended the FAA remove details in
proposed Sec.  23.500(d) that describe what parts of the system should
be subject to which loads because this is design specific and should be
covered in the means of compliance.
    The FAA agrees with EASA and the Associations to revise proposed
Sec.  23.500(d)(1), (d)(2), and (d)(3) and adds the phrase ``the
airplane is subjected to expected limit airloads'' to the end of Sec.
23.2250(d). This change aligns with EASA's recommendation and assists
in harmonization with EASA's proposed rule. The FAA considers these
suggestions to be more in line with the original intent of the
performance standards. Therefore, the FAA adopts the changes proposed
by the commenters.
    Textron suggested the FAA remove the Sec.  23.500(d)(1) requirement
that the supporting structure is loaded with limit airloads while the
control system is loaded, which the commenter noted has historically
never been a part 23 requirement. Textron further suggested the FAA
change the phrase ``controls are'' in both subparagraphs (2) and (3) to
``control system is'' to further specify that this is a control system
test. Textron commented that the word ``controls'' could imply
something other than the entire system is the intent.
    As noted above in this section, the FAA removes paragraphs
paragraph (d)(1), (d)(2) and (d)(3). The FAA adopts the terminology
``control system'' in the revised proposed Sec.  23.500(d).
    EASA also suggested the FAA consider moving the general principle
for doors, canopies, hatches, and access panels from proposed Sec.
23.750(f) to a new Sec.  23.2250(e).
    The FAA concurs with EASA's recommendation to move the general
principle for doors, canopies, hatches, and access panels from proposed
Sec.  23.750(f) to a new Sec.  23.2250(e). The requirement is more
appropriate in this section because it states a general design
principle rather than a requirement relating to emergency evacuation.
The FAA also notes that making this change further helps to harmonize
FAA and EASA regulations.
l. Protection of Structure (Proposed Sec.  23.505/Now Sec.  23.2255)
    In the NPRM, proposed Sec.  23.505 (now Sec.  23.2255) would have
required an applicant to protect each part of the airplane, including
small parts such as fasteners, against deterioration or loss of
strength due to any cause likely to occur in the expected operational
environment. Proposed Sec.  23.505 would have also required each part
of the airplane to have adequate provisions for ventilation and
drainage and would require an applicant to incorporate a means into the
airplane design to allow for required maintenance, preventive
maintenance, and servicing.
    Textron recommended clarifying the intent of proposed Sec.
23.505(a) by including a reference to specific sources of damage
because it is unclear whether the proposed rule would be an increase
from what was previously required.
    The FAA considered Textron's comment. However, as far back as 1949
(Sec.  3.295, ``Protection''), the regulations required all members of
the structure to be ``suitably protected against deterioration or loss
of strength in service due to weathering, corrosion, abrasion, or other
causes. . . .'' The CAR 3 requirement was included in the 1965
recodification as former Sec.  23.609, which included a non-exhaustive
list of possible causes of deterioration. In the NPRM, the FAA removed
the listed examples, but maintained the requirement to account for
deterioration or loss of strength due to ``any cause likely to occur.''
    Textron further stated that it is unclear whether the phrase
``expected operational environment'' is intended to include any
environment that might occur during failure conditions, or just the
environment during normal operating conditions. Textron recommended
replacing the phrase ``expected operational environment'' with
``intended operational environment'' or ``normal operational
environment.''
    The FAA considered Textron's recommendation to change ``expected
operational environment'' to ``intended operational environment'' or
``normal operational environment.'' The FAA did not intend to limit
this requirement only to the normal operational environment because, if
the failure conditions are an expected environment, then an applicant
should consider those conditions and protect the structure.
Deterioration or loss of strength due to corrosion, weathering, and
abrasion are all examples of failure conditions because capability has
been degraded. For many years, the rule has expressly required
consideration of these causes. It was an expected environment for items
to be corroded, weathered, and abraded, but applicants had to consider
any other causes too.
m. Materials and Processes (Proposed Sec.  23.510/Now Sec.  23.2260)
    In the NPRM, proposed Sec.  23.510 (now Sec.  23.2260) would have
required--
     An applicant to determine the suitability and durability
of materials used for parts, articles, and assemblies, the failure of
which could prevent continued safe flight and landing, while accounting
for the effects of likely

environmental conditions expected in service; and
     The methods and processes of fabrication and assembly used
to produce consistently sound structures and, if a fabrication process
requires close control to reach this objective, an applicant would have
to perform the process under an approved process specification.
    Additionally, proposed Sec.  23.510 would have required an
applicant to justify the selected design values to ensure material
strength with probabilities, accounting for--
     The criticality of the structural element; and
     The structural failure due to material variability, unless
each individual item is tested before use to determine that the actual
strength properties of that particular item would equal or exceed those
used in the design, or the design values are accepted by the
Administrator.
    Proposed Sec.  23.510 would have required a determination of
required material strength properties to be based on sufficient tests
of material meeting specifications to establish design values on a
statistical basis. Proposed Sec.  23.510 would have also required an
applicant to determine the effects on allowable stresses used for
design if thermal effects were significant on an essential component or
structure under normal operating conditions.
    Textron commented that, as proposed, the regulatory text in
paragraph (a) was unclear as to whether an applicant must account for
the effects of likely environmental conditions expected in service on
parts, articles, and assemblies. Textron proposed combining the two
sentences in paragraph (a) to clarify the FAA's intent for the effect
of specific environmental conditions on parts, articles, and assemblies
to be considered in determining the suitability and durability of
materials.
    The FAA concurs with Textron's comment regarding the lack of
clarity in paragraph (a), and revises the regulation accordingly.
Although the revision creates a slight disharmony with EASA's proposed
rule language, the intent of the two regulations remains the same, and
the change helps to clarify the FAA's intent.
    Textron also requested the FAA to replace the word ``essential''
with the word ``critical''. The commenter stated the word ``essential''
has not been used or defined historically in part 23 structural
compliance, whereas the word ``critical'' is used more frequently and
is better defined.
    Based on Textron's comment for clarity, the FAA revises Sec.
23.2260(e) to replace the word ``essential'' with the word
``critical'', since ``critical'' is a more common and widely used term
of art amongst structural engineers than ``essential.'' Specifically,
the failure of a critical component or structure is potentially
catastrophic.
    In the public meeting, Aspen Avionics asked the FAA to clarify
whether the requirement in proposed paragraph (b) to perform the
process under an ``approved process specification'' refers to an FAA-
approved process specification or an accepted industry standard or some
other approved process specification. Aspen Avionics also commented on
proposed paragraph (d), which stipulates that if material strength
properties are required, a determination of those properties must be
based on sufficient tests of material meeting the specifications. Aspen
Avionics questioned whether this requirement applies to the applicant
or whether the applicant can rely on statements from a manufacturer--
i.e., Aspen asked the FAA to clarify who has to do what testing for the
materials. Aspen also asked whether the testing requirement applies to
primary, secondary, or tertiary structure.
    Regarding Aspen Avionics' request for clarification of what
constitutes an approved process specification for paragraph (b), the
FAA does not intend any change from current practices under former
regulation Sec.  23.605(a), where nearly identical language was used.
The process specification is ``approved'' by the FAA, and the FAA
expects to have access to the specification in order to review and
determine whether it contains sufficient control to substantiate
compliance with the regulation. The specification may be proprietary to
the OEM or sub-contractor, but should have formal document approval and
control procedures like other engineering reports, documents and
drawings necessary for the type design.
    As for Aspen Avionics' question regarding the test requirements and
whether the requirement is for primary, secondary, or tertiary
structure, the FAA does not intend any change from current practices
under former regulation Sec.  23.613(a), where nearly identical
language was used. The TC holder is responsible for data used to
substantiate its type design. Whether the required testing is performed
by the OEM or a sub-contractor does not matter as the FAA holds the OEM
responsible, and expects the data to be available for FAA review to
ensure compliance with the regulation. This requirement for
statistically based material properties applies to any airplane primary
structure. Existing published FAA guidance and widely used industry
practices should be consulted for the finer divisions of structure,
such as secondary and tertiary, and the material properties typically
used.
n. Special Factors of Safety (Proposed Sec.  23.515/now Sec.  23.2265)
    In the NPRM, proposed Sec.  23.515 (now Sec.  23.2265) would have
required an applicant--
     To determine a special factor of safety for any critical
design value that was uncertain, used for a part, article, or assembly
likely to deteriorate in service before normal replacement, or subject
to appreciable variability because of uncertainties in manufacturing
processes or inspection methods;
     To determine a special factor of safety using quality
controls and specifications that accounted for each structural
application, inspection method, structural test requirement, sampling
percentage, and process and material control; and
     To apply any special factor of safety in the design for
each part of the structure by multiplying each limit load and ultimate
load by the special factor of safety.
    The Associations recommended changing Sec.  23.515(a) by requiring
special factors of safety be ``established and applied'', rather than
determined, by the applicant. Additionally, they suggested the language
of the regulation focus on critical design values ``affecting
strength.''
    The FAA has used ``determine'' in numerous other places in the
NPRM. The commenters' suggested change would not imply a different
meaning. As for the commenters' suggestion that the term ``critical
design value'' should be limited to those values ``affecting
strength,'' there may be other critical design values aside from
strength that warrant the use of special factors of safety. For
example, former part 23 specified bearing factors for certain
applications. These were intended to account for not only strength, but
also for durability and consideration of possible dynamic loading. In a
performance-based standard where these factors are not specified, it is
necessary to make sure that future designs, materials, and
applications, not yet envisioned, account for any critical ``design
values,'' in the same way the former regulations account for known
critical values in those applications today. The FAA adopts Sec.
23.2265(a) with minor modifications.

    Air Tractor commented that proposed Sec.  23.515(b) added
unwarranted specificity and is worded such that the special factor must
account for each inspection method, whether or not it is critical. Air
Tractor further commented that certain conditions, such as structural
test requirements, sampling percentages, and process and material
controls, would be defined in a quality system approved under a
production certificate (PC), not as part of a type design. Air Tractor
contended that a type design should be approved independently of any
quality system or production system requirements.
    The FAA agrees with Air Tractor that conditions, such as structural
test requirements, sampling percentages, and process and material
controls, would be defined in a quality system that is approved under a
PC. However, there are instances where those items are defined by type
design or inspection methods in an approved type design. As with the
former Sec.  23.621, ``Casting factors,'' special casting factors of
safety are to be applied to any structural casting, not just critical
ones. The specific casting factor used in all those cases is
inseparably tied to the applicable tests and inspections, both of which
include sampling percentages specified for the part being produced.
Former Sec.  23.621(a) required these factors to be defined in the type
design, and they are in addition to whatever tests and inspections are
required for foundry quality control. Therefore, proposed Sec.
23.515(b) is not substantively different from the former regulations.
    The FAA generally agrees with Air Tractor's comment that approval
of a type design is independent of any quality system or production
system requirements. However, as explained previously in this section,
the special factor of safety used to substantiate the type design is
approved for use based completely on the part criticality, inspections,
tests, and sampling percentages specified for a particular part.
    Additionally, the Associations recommended changing proposed Sec.
23.515(b)(1) by replacing ``structural'' application with ``kind of''
application. The commenters contended it would ensure that special
factors of safety continue to be applied in the same manner as they are
applied in the former rule, while also providing for more flexibility
for new materials and construction techniques.
    The FAA agrees with the Associations that the term ``structural''
in proposed Sec.  23.515(b)(1) should be revised. However, the FAA
believes the words ``type of'' is more accurate than ``kind of'' in
this application, and revises the text of Sec.  23.2265(b) accordingly.
    The Associations recommended changing proposed Sec.  23.515(c) to
require a factor of safety established under proposed Sec.  23.330(b)
to be multiplied by the highest pertinent factor of safety established
under proposed Sec.  23.515(b). The commenters explained that this
change would ensure special factors of safety are applied in the same
manner as they are applied in the former rule, while also providing for
more flexibility for new materials and construction techniques.
    The FAA disagrees with the Associations as such a change has led to
convoluted regulations in the past. Further, the limit and ultimate
loads are clearly defined in this subpart, so this cross-reference is
unnecessary.
    Additionally, EASA noted that although the strict wording in former
part 23 and CS 23 did not require special factors to be applied to
ultimate loads that do not have corresponding limit loads (e.g.,
emergency landing conditions), this is not reflected in the NPRM.
Referring to proposed Sec.  23.515(c), EASA noted that former part 23
and CS 23 use the highest pertinent special factor, instead of any
special factor as proposed in the NPRM. EASA suggested that
coordination is necessary for harmonization.
    The FAA does not agree with EASA's assertion that a narrow
interpretation of former part 23 would not require special factors of
safety to be applied to ultimate loads that do not have corresponding
limit loads. Former Sec.  23.625(d) required the attachments of seats,
berths, and safety belts and harnesses to multiply the inertia loads in
the emergency landing conditions in former Sec.  23.561 by a special
factor of safety (i.e., fitting factor) of 1.33. However, the FAA
concurs with EASA that new part 23 should require the use of the
``highest pertinent'' special factor of safety, and not ``any'' special
factor of safety. Therefore, the FAA revises Sec.  23.2265(c)
accordingly.
    Additionally, upon further review, the FAA finds that the proposed
wording in Sec.  23.515(c) appears to require an applicant to multiply
not only each ultimate load by the special factor of safety, but also
each limit load by the same factor even though sometimes there is no
corresponding limit load. Therefore, the FAA also revises Sec.
23.2265(c) to state that the special factor of safety is applied
regardless of whether there is a limit load condition corresponding to
the ultimate load condition. Although the FAA's language may not be
harmonized with EASA's NPA, the intent is the same.
o. Emergency Conditions (Proposed Sec.  23.600/Now Sec.  23.2270)
    In the NPRM, proposed Sec.  23.600 (now Sec.  23.2270) would have
required--
     The airplane, even if damaged in emergency landing
conditions, to provide protection to each occupant against injury that
would preclude egress;
     The airplane to have seating and restraints for all
occupants, consisting of a seat, a method to restrain the occupant's
pelvis and torso, and a single action restraint release, which meets
its intended function and does not create a hazard that could cause a
secondary injury to an occupant;
     The airplane seating, restraints, and cabin interior to
accommodate likely flight and emergency landing conditions and should
not prevent occupant egress or interfere with the operation of the
airplane when not in use;
     Each baggage and cargo compartment be designed for its
maximum weight of contents and for the critical load distributions at
the maximum load factors corresponding to the determined flight and
ground load conditions; and
     Each baggage and cargo compartment to have a means to
prevent the contents of the compartment from becoming a hazard by
impacting occupants or shifting, and to protect any controls, wiring,
lines, equipment, or accessories whose damage or failure would affect
operations.
    Air Tractor, commenting on proposed Sec.  23.600(a), said the NPRM
preamble suggested that future certification endeavors will require
more effort (e.g., possibly full-scale crash testing of the fuselage)
to meet necessary requirements. Air Tractor also noted that inertial
loads likely to occur in an emergency landing were not defined.
Additionally, Air Tractor presumed the conditions defined in former
Sec.  23.561 would be accepted, but doing so would not make things
under the proposed rule any easier, faster, or less expensive. Air
Tractor also claimed that should some other inertial loads likely to
occur in an emergency landing be proposed, the applicant should expect
a protracted discussion with the FAA to defend any differences.
    The FAA disagrees that future certification endeavors will require
more effort and possibly full-scale crash testing of the fuselage to
meet the requirements. Existing conditions of current static and
dynamic testing would remain as a means of compliance. Proposed Sec.
23.600(a) would

not have required full-scale crash testing of the fuselage. The FAA's
intent was to allow for an evaluation of a ``crash landing''
considering the performance of the entire airframe, safety equipment,
and occupant. The former requirements only required evaluation of the
seat from the floor up, and the restraints, using generic floor
impulses independent of airframe reaction. Additionally, the FAA did
not define inertial loads because one of the goals of creating
performance-based standards was to move away from mandated prescriptive
standards, which inhibit innovation and safety enhancing technology
adoption. The inertial loads likely to be encountered will be contained
in the means of compliance. An applicant may propose inertial loads
other than those contained in industry standards already accepted by
the Administrator, and substantiate why they are adequate,
representative, and equally safe as accepted loads. This rule will
allow applicants to evaluate crash landing conditions considering the
entire airplane and its performance, instead of limiting applicants to
just these tests.
    The NTSB noted the NPRM stated that proposed Sec.  23.600 would
capture the safety intent of former Sec. Sec.  23.561 and 23.562, which
the FAA described as containing prescriptive design standards. The NTSB
disagreed that former Sec. Sec.  23.561 and 23.562 are prescriptive
design standards, and stated former Sec. Sec.  23.561 and 23.562 were
performance-based standards that do not specify any elements of the
design, but instead prescribed a test and measureable levels of
performance needed to ensure safety.
    The NTSB shared the FAA's concern regarding consideration of
occupiable space in a post-crash situation, and agreed former standards
do not address these issues. However, the NTSB disagreed with the FAA's
suggestion that analysis techniques available in the automotive
industry are transferable to new airplane designs. The NTSB said it is
likely that differences between airframe and automotive structures will
require a significant number of full-scale aircraft crash tests before
analytical techniques have been validated to the point they can be used
as means of compliance. Pointing to NTSB Safety Recommendation A-11-3,
which it issued in 2011 after conducting a study of the performance of
airbags in general aviation airplane, the NTSB recommended the FAA
consider the variation in the sizes and anthropometry of airplane
occupants when evaluating a proposed means of compliance.
    The FAA understands the NTSB's comments, but does not agree. Former
Sec. Sec.  23.561 and 23.562 assessed only the seat, attachment,
restraints, and head strike. The generic floor impulse used did not
take into account the variables inherent to the airplane, such as the
ability to protect the survivable volume, crushable airplane structure,
or features that absorb impact energy or offer the ability to evaluate
how all of these variables can work together to enhance
crashworthiness. This rule will allow a more holistic approach to
crashworthiness. Not prescribing a specific seat test opens the door
for future technology and advances in analytical techniques to
demonstrate equivalent and even enhanced safety, utilizing all advances
available to the engineer. At the same time, until these enhanced
techniques become available and proven, the existing seat test methods
are still acceptable for showing compliance with this rule and will be
contained in a means of compliance.
    Additionally, the FAA will accept the former regulations as an
acceptable method of compliance, despite their limitations. Testing in
accordance with the former regulations has provided a certain level of
safety for many years; therefore, continuing to accept them for future
designs will maintain that level of safety. However, the FAA contends
that having a prescriptive set of tests in the rule has prevented the
industry from moving beyond this one standard of protecting occupants.
This is because the former regulations required a very specific seat
sled test; detailing seat mounting misalignment, impulse force peak and
rise times, and maximum forces allowed to be experienced by the
restraint system, and the occupant's lumbar spine among other things.
Due to the rule specifying all these details, it is nearly impossible
for the FAA to find equivalency in applicants proposed alternatives. By
changing the requirement from a prescriptive test to the safety intent
behind the test, the FAA will only need to evaluate whether new methods
meet the safety intent, and not have to evaluate their relative safety
against the former requirements. The determination that likely crash
scenarios do not generate loads on the occupants that exceed the limits
of human injury was the basis of the former rule language, and how the
test and crash impulse was derived. It was a combination of various
scenarios, represented by one specific set of tests. The new rule will
allow a holistic approach to enable designs to achieve occupant
protection more effectively.
    While the automotive industry generally has a more-developed
crashworthiness analysis capability than that used in the aviation
industry, the FAA wants to allow for incorporation of holistic
crashworthiness in addition to conventional compliance. The FAA notes
the NTSB's concern that automotive technology will not directly
transfer to aerospace applications because it requires significant
numbers of full-scale aircraft crash tests for validation to yield the
confidence in the analytical techniques. However, the FAA disagrees.
The FAA has not yet determined how much and what type of validation
will be required for a given crash scenario. This determination will
depend on the particular design and what the validation is attempting
to demonstrate. The automotive and other industries have gained a lot
of knowledge on what is needed to demonstrate valid models using
dynamic transient analysis. The FAA believes that the knowledge from
these industries can be leveraged to reduce or eliminate the need for
full-scale aircraft crashes for validation. For example, there may be
scenarios where only a small part needs validation for demonstration of
its energy absorption. This rule will provide an applicant with the
option to examine the performance of more than just the seat and
restraints, and avoids defining methods of restraint. This will allow
consideration of a myriad of ways to protect an occupant in an
emergency landing, such as using airbags.
    Also, the FAA notes the NTSB's recommendation that the FAA consider
the variation in the sizes and anthropometry of airplane occupants when
evaluating a proposed means of compliance. This would be an increase in
the burden to the manufacturers, and this burden has not been
justified.
    Several organizations commented on proposed Sec.  23.600(b).
Kestrel noted that proposed Sec.  23.600(b)(1) referred to impact at
stall speed, but did not specify the configuration and atmospheric
conditions associated with this stall speed. Kestrel also requested
clarification on whether applicants must design for stall speed in
icing conditions.
    The FAA revises the proposed rule language. The configuration and
atmospheric conditions will be located in the means of compliance based
on a determination of the conditions that are likely to occur.
    In discussing proposed Sec.  23.600(b)(1), ICON questioned whether
industry can deliver on this ``new requirement.'' Textron noted that
proposed Sec.  23.600(b) referred to the emergency landing conditions
specified in paragraph (a), which would mean the items of mass

specified in paragraph (a) must meet the dynamic conditions specified
in paragraph (b). Textron noted this is a significant departure from
the former rule and assumed it was not the FAA's intent to require
dynamic conditions for items of mass. Similarly, the Associations
commented that Sec.  23.600(b) would be a new requirement without
foundation. They believed the FAA intended to apply the requirement
only to occupant restraint systems.
    The FAA agrees with Textron and others that an unintentional new
requirement would have been imposed by the proposed wording of
paragraph (b)(1). The FAA did not intend to apply dynamic loading
requirements to items of mass that previously required accounting only
for static loads. The FAA modifies the text of paragraph (b) to refer
only to subparagraphs (a)(1) and (a)(2) instead of all of paragraph
(a), thereby eliminating reference to items of mass.
    EASA said the ``dynamic'' condition specified in paragraph (b)(1)
should be in the means of compliance, not in the rule. ICON noted that
proposed Sec.  23.600(b)(1) would require a very long list of variables
be considered in an impact, which seems prohibitively difficult to
achieve with any degree of confidence.
    The FAA agrees with ICON and EASA. The long list of variables is
reduced to simply ``emergency landing'' conditions, which can then be
further detailed as part of the means of compliance.
    Transport Canada said the requirement in proposed Sec.
23.600(b)(2) appeared inaccurate. It noted that what must not exceed
established injury criteria for human tolerance are the loads
experienced by the occupant, not the emergency landing conditions.
Transport Canada recommended a rewrite of paragraph (b)(2) that would
state that the occupants would not experience loads which exceed
established injury criteria for human tolerance due to restraint or
contact with objects in the airplane.
    The FAA agrees with Transport Canada. The FAA adopts the
recommended language and revises the rule to clarify it is the loads
experienced by the occupant, not the emergency landing conditions that
should not exceed the established injury criteria for human tolerance.
    BendixKing suggested replacing the word ``restraints'' with
``protection'' in the two instances the word occurs in proposed Sec.
23.600(c). BendixKing suggested this change is appropriate because the
intent of the rule is to ensure crash protection for the occupant,
which may or may not be what is understood to be restraint. BendixKing
also stated it is important not to assume a particular solution, but to
focus on the safety intent or occupant protection from harmful motion
during an impact. Therefore, it suggested words used in proposed Sec.
23.600(d) like ``restraint,'' ``pelvis,'' ``torso,'' be replaced with
language like ``protection'' or ``securing the occupant from harm.''
EASA commented that proposed Sec. Sec.  23.600(c) and (d) should be an
accepted means of compliance, not regulatory requirements. The
Associations commented that the language in proposed Sec.  23.600(d)
should be aligned with current DOT practices related to automobile
safety. The commenters noted the proposed language may preclude some
better methods of safety in crashworthiness and might unnecessarily
restrict design capabilities.
    The FAA agrees with BendixKing that using design-specific solution
terminology such as ``restraints'' is not appropriate for a
performance-based regulation. While the occupant needs to be
restrained, restraints should be considered on a broader basis. The FAA
also agrees with EASA that the portions of Sec. Sec.  23.600(c) and (d)
that use design-specific terminology should be in the means of
compliance. As such, the FAA will use more generic terms like
``protection'' or ``occupant protection system'' in lieu of the design-
specific terms proposed in paragraphs (c) and (d), to allow for other
methods of compliance to meet the safety intent of the rule. Finally,
due to these word changes, the FAA moved the consideration of ``ground
loads'' from paragraph (d) to paragraph (c).
    Transport Canada noted the reference to water loads is missing in
paragraphs (d) and (e)(1). Transport Canada recommended those
paragraphs be modified by adding the word ``water'' in the phrase ``For
all flights and ground loads.''
    The FAA considered Transport Canada's comment, but one of the goals
of adopting performance-based regulations is to remove some of the
specificity, to enable the flexibility to adapt to changing
technologies and environments. Specifying every possible landing
surface would not align with this goal. Therefore, the FAA is not
incorporating Transport Canada's changes into the final rule.
    Transport Canada also commented that proposed Sec.  23.600(e)
should provide a performance-based standard for the requirements in
former Sec.  23.787(b) for baggage or cargo sharing the same
compartment as passengers.
    The FAA agrees baggage and cargo sharing the same compartment with
passengers should be restrained. However, a change to the proposed rule
is not necessary to address this. Section 23.2270(a) of this rule
requires restraint of items of mass within the cabin utilizing static
inertial loads, including baggage or cargo that is in the cabin.
    The Associations and Textron addressed the requirement in proposed
Sec.  23.600(e)(3) that baggage and cargo compartments must protect
controls, wiring, lines, equipment, or accessories whose damage or
failure would ``affect operations.'' Textron noted that any kind of
damage or failure would arguably ``affect operations,'' making it
difficult to comply with the rule. Textron recommended the FAA qualify
the requirement by adding the word ``safe'' in front of ``operations.''
The Associations recommended the FAA delete the word ``any'' in front
of ``controls,'' delete the word ``affect,'' and add the words ``limit
safe'' in front of ``operations.''
    The FAA agrees with the comments from Textron and the Associations
and is adding ``safe'' to modify ``operations.'' Adopting this change
will harmonize the text with EASA's proposed rule language. The FAA
will not adopt the other recommended changes as they would not have a
substantive effect on the rule.
    Daher commented generally on Sec.  23.600, indicating the phrase
``rolling and pitching'' would be more appropriate than ``pitching and
yawing.'' Daher did not indicate where these phrases were, but the FAA
believes it is referring to a statement made in the NPRM preamble
discussion of proposed Sec.  23.600 that stated dynamic seat testing
requirements address the ability of seat assemblies to remain attached
to the floor, even when the floor shifts during impact. Pitching and
yawing of the seat tracks during dynamic seat tests demonstrates the
gimbaling and flexibility of the seat.
    Furthermore, the FAA believes Daher was specifically inferring that
``rolling and pitching'' would be more appropriate in Sec.
23.2270(b)(1) because the rule language in former Sec.  23.562 required
the seat rails to be misaligned by 10 degrees in the ``pitch'' and
``roll'' axis, not the ``pitch'' and ``yaw'' axis. The FAA's intent was
not simply to mimic the original Sec.  23.562 misalignment
requirements, but to identify static airplane orientation at impact in
order to assess the level of airframe crushing and energy absorption.
However, based on other comments on proposed Sec.  23.600, the FAA has
removed specific references to

the terms ``flight path angle,'' ``flight pitch angle,'' ``yaw,'' and
``airplane configuration.'' These parameters will be included in the
means of compliance.
    An individual commenter in the seatbelt manufacturing industry
suggested putting a life limit of 10 years on seatbelts, because the
webbing loses its strength due to exposure to UV lights and heat. The
FAA notes that a seat belt life limit is not within the scope of this
rulemaking. The details of seat belts and seat belt webbing materials
are controlled by industry standards and Technical Standard Orders
(TSOs). Additionally, specifying those types of design-specific
solutions is counter to performance-based regulations.
5. Subpart D--Design and Construction
a. Flight Control Systems (Proposed Sec.  23.700/Now Sec.  23.2300)
    In the NPRM, proposed Sec.  23.700 (now Sec.  23.2300) would have
required an applicant to design airplane flight control systems to
prevent major, hazardous, and catastrophic hazards. Proposed Sec.
23.700 would have required an applicant to design trim systems to
prevent inadvertent, incorrect, or abrupt trim operation. In addition,
proposed Sec.  23.700 would have required an applicant to design trim
systems to provide a means to indicate--
     The direction of trim control movement relative to
airplane motion;
     The trim position with respect to the trim range;
     The neutral position for lateral and directional trim; and
     For all airplanes except simple airplanes, the range for
takeoff for all applicant requested center of gravity ranges and
configurations.
    Proposed Sec.  23.700 would have also required an applicant to
design trim systems to provide control for continued safe flight and
landing when any one connecting or transmitting element in the primary
flight control system failed, except for simple airplanes.
Additionally, proposed Sec.  23.700 would have required an applicant to
design trim systems to limit the range of travel to allow safe flight
and landing, if an adjustable stabilizer is used.
    Furthermore, proposed Sec.  23.700 would have required the system
for an airplane equipped with an artificial stall barrier system to
prevent uncommanded control or thrust action and provide for a
preflight check. The FAA also proposed requiring an applicant seeking
certification of a level 3 high-speed or level 4 airplane to install a
takeoff warning system on the airplane, unless the applicant
demonstrates that the airplane, for each configuration, could takeoff
at the limits of its trim and flap ranges.
    In light of comments received, the FAA revises proposed Sec.
23.700 to withdraw paragraphs (a)(1) and all its subparagraphs, rename
proposed paragraph (a)(2) as (a)(1), add new paragraph (a)(2), withdraw
proposed paragraphs (b)(3), (b)(4), and paragraphs (c) and (d) and all
their subparagraphs. This section discusses these changes in more
detail.
    Textron and Kestrel questioned how the term ``prevent'' was
intended to be used with the system safety analysis terms ``major,''
``hazardous,'' and ``catastrophic.''
    The FAA acknowledges the term ``prevent'' caused confusion in
proposed Sec.  23.700(a)(1), and replaces ``prevent'' with ``protect
against'' in Sec.  23.2300(a)(2). The FAA did not intend to require
additional safety analysis in this section, as suggested by these
comments.
    The Associations, Kestrel, Air Tractor, and Textron expressed
concern that proposed Sec.  23.700 appears to require that applicants
perform System Safety Assessments (SSAs) for traditional mechanical
flight control systems that have never been subject to this requirement
in the past. They note this would impose substantial new costs on
applicants. The commenters acknowledge that SSAs would be appropriate
for unconventional designs, such as fly-by-wire systems.
    The FAA did not intend to imply that a safety analysis would be
required for all flight control systems, including simple mechanical
flight control systems in proposed Sec.  23.700(a). The FAA deletes the
terms that could have been associated with safety analysis and revises
Sec.  23.2300(a)(2) to require the applicant to design airplane flight
control systems to protect against likely hazards. The FAA intends
``protect against likely hazards'' to be a high-level requirement to
consider potential hazards to the flight control system, and
incorporate features in the design to protect against these hazards.
One way for a traditional flight control system to satisfy this would
be to use the former part 23 regulations, which addressed hazards such
as jamming, chafing, interference, incorrect assembly, asymmetric
flaps, control system lock inadvertent engagement in flight, etc.
    The FAA agrees with the comments stating that safety analysis is
necessary, as required by Sec.  23.2510 (proposed as Sec.  23.1315),
for fly-by-wire flight control systems, powered flight control systems,
and automatic flight control systems. The FAA withdraws the safety
analysis requirement in Sec.  23.2300 because Sec.  23.2510 adequately
addresses the requirement for safety analysis. The FAA notes the
applicability of the Sec.  23.2510 safety analysis requirements will be
addressed as a means of compliance, similar to the current practice in
AC 23.1309-1E.
    The Associations and Textron recommended the FAA eliminate proposed
paragraph Sec.  23.700(a)(1)(iii), which lists ``flutter'' as one of
the possible major, hazardous or catastrophic hazards, because it is
redundant and unnecessary as the safety intent of flutter is covered in
the aeroelastic section, proposed Sec.  23.410 (now Sec.  23.2245). The
FAA agrees because Sec.  23.2245 ``Aeroelasticity'' adequately
addresses flutter for normal operation, exceedances and failure
conditions. The FAA also withdrew the other examples of hazards in
proposed Sec.  23.700(a)(1) so that they can be addressed more
completely in means of compliance.
    The Associations and Textron also questioned the use of the term
``misconfiguration'' in proposed Sec.  23.700(a)(1)(v). Textron asked
the FAA to clarify whether the term refers to items like rigging and
installation or items like wing configurations (e.g., flaps, speed
brakes) and trim. The Associations recommended ``misconfiguration'' be
replaced with ``misrigging'' for clarity and anticipated the
traditional misrigging practices would continue to apply. Proposed
Sec.  23.700(a)(1)(v) was intended to address the requirement from
former Sec.  23.685(d) that each element of the flight control system
must have design features, or must be distinctively and permanently
marked, to minimize the possibility of incorrect assembly that could
result in malfunctioning of the control system. The FAA agrees that
``misrigging'' incorporates the intent of this requirement more clearly
than ``misconfiguration.'' However, the FAA has decided to remove
proposed Sec.  23.700(a)(1)(v) from the final rule as discussed.
    With the withdrawal of the list in proposed Sec.  23.700(a)(1), the
FAA renumbers proposed Sec.  23.700(a)(2) as Sec.  23.2300(a)(1) and
adds a new paragraph (a)(2).
    Textron commented that proposed Sec.  23.700(a)(2) could seem
reasonable for all systems and recommended moving the paragraph to
proposed Sec.  23.1305 (now Sec.  23.2505).
    The FAA disagrees with applying proposed Sec.  23.700(a)(2) to all
systems and equipment because the requirement to ``operate easily,
smoothly and positively enough to allow normal operation'' does not
apply to all

systems. For example, evaluating a flight data recorder for
``smoothness'' would not make sense. The FAA revises Sec.
23.2300(a)(1) to be consistent with former Sec.  23.671(a) because it
states the intent of the requirement more clearly.
    The Associations proposed revising Sec.  23.700(b) to state ``the
trim systems must . . .'' instead of ``[t]he applicant must design trim
systems to.'' They made a similar comment on proposed Sec.  23.700(a).
    The FAA used ``the applicant must design . . .'' throughout the
NPRM. The FAA retains this wording because it's consistent with part 21
to impose the obligation on the applicant.
    Textron noted that proposed Sec.  23.700(b)(1) was a general
concept that should actually apply to all systems, and therefore
recommended changing the word ``trim'' to ``system,'' and moving
proposed Sec.  23.700(b)(1) to proposed Sec.  23.1305. Textron also
questioned whether the term ``prevent'' in proposed Sec.  23.700(b)(1)
meant ``meet the associated requirements of a system safety
assessment.'' Textron recommended rewriting proposed paragraph (b)(1)
to provide that the applicant must design trim systems to meet system
safety requirements, according to the assessment mandated by proposed
Sec.  23.1310, and that the evaluation of the system shall include
hazards caused by inadvertent (uncommanded) trim operation and
incorrect (motion in the opposite direction than commanded) trim
operations.
    The FAA notes the requirement to ``prevent inadvertent, incorrect,
or abrupt system operation'' would not be appropriate for some systems.
For example, evaluating a flight data recorder for ``abrupt system
operation'' would not make sense. Therefore, the FAA did not
incorporate Textron's recommendation in this rule. The FAA also
declines to move the regulation to proposed Sec.  23.1305 (now Sec.
23.2505) because that section applies to all systems, while this
requirement is only intended for flight control trim systems. In light
of Textron's comment, the FAA has changed ``prevent'' to ``protect
against'' for consistency with Sec.  23.2300(a)(2). However, the FAA
did not incorporate Textron's recommendation to change proposed Sec.
23.700(b)(1) because this section does not require safety analysis.
This section applies to all trim systems while Sec.  23.2510 does not
apply to trim systems that are considered ``flight control surfaces and
their simple systems'' as discussed in AC 23.1309-1E.
    Several organizations commented on proposed Sec.  23.700(b)(3). The
Associations recommended deleting proposed paragraph (b)(3). They
stated that addressing the loss of any single flight control link with
traditional mechanical flight controls has provided a substantial level
of safety and as new stability and fly-by-wire systems are discussed,
it will be increasingly important to develop adequate means of
compliance in acceptable documents.
    EASA asserted the proposed requirement to have a trim system as a
means of control in case of failure of a connecting or transmitting
element was too prescriptive and should be captured by the intent that
a flight control system must prevent major, hazardous, and catastrophic
hazards for likely failure conditions.
    The FAA agrees that proposed Sec.  23.700(b)(3) was too
prescriptive because means other than trim could be used to safely
control the airplane when any one connecting or transmitting element in
the primary flight control system fails. The requirement to protect the
airplane from loss of control when any one connecting or transmitting
element in the primary flight control system fails is captured in Sec.
23.2300(a)(2) at a high level. Therefore, the FAA withdraws proposed
Sec.  23.700(b)(3). In addition, the FAA adds ``if installed'' to Sec.
23.2300(b) in light of the comments that future designs may not use
trim systems.
    Transport Canada observed that VLA rules permit trim systems that
do not provide safe flight and landing following failure of the primary
control system. Transport Canada said it did not believe this
alleviation should be carried into the part 23 revisions, even for
small airplanes. Transport Canada recommended the level of safety for
trim system failures be raised for simple airplanes.
    As discussed elsewhere, the FAA has decided to withdraw the simple
category, proposed in Sec.  23.5(d), and also to withdraw proposed
Sec.  23.700(b)(3) because Sec.  23.2300(a)(2) captures the
requirement. The FAA has determined that the level of safety for trim
system failures should not be raised for entry-level airplanes. One of
the goals of the NPRM was to provide appropriate standards for ``entry-
level airplanes'', and the FAA finds Sec.  23.2300(a)(2) meets that
goal. As discussed in this section, Sec.  23.2300(a)(2) requires the
applicant to design airplane flight control systems to protect against
likely hazards. While the FAA's intent is that flight control systems
that meet the former part 23 requirements adequately protect against
the likely hazard of failures in any one connecting or transmitting
element in the primary flight control system, those airplanes certified
under EASA's Certification Specification--Very Light Aeroplanes (CS-
VLA), were not certified under part 23. Rather, they were imported to
the U.S. and certificated as special class airplanes in accordance with
Sec.  21.17(b). Under Sec.  23.2300(a)(2), these airplanes could be
certified under part 23, using the CS-VLA to meet the requirements.
    Upon further consideration of proposed Sec.  23.700(b)(4), the FAA
decided the safety intent of the requirement to limit the range of
travel to allow safe flight and landing, if an adjustable stabilizer is
used, is already incorporated in the regulations through the
requirement for the applicant to design airplane flight control systems
to protect against likely hazards. The proposed requirement was
prescriptive and may not be appropriate for non-traditional airplane
designs. Therefore, the FAA withdraws proposed Sec.  23.700(b)(4).
    The Associations asserted including specific information for the
verification of stall barrier systems in proposed Sec.  23.700(c) is
not beneficial because the issue being addressed is already covered by
``flight control reliability aspects.'' The commenters also noted the
simple checks being specified may not be appropriate for all stall
barrier systems and that addressing stall barrier flight controls would
be better detailed in means of compliance. The commenters recommended
deleting proposed Sec.  23.700(c).
    The FAA agrees that there is no benefit to including Sec.
23.700(c) because Sec.  23.2510 adequately addresses stall barrier
system failure conditions and checks for latent failures. Therefore,
the FAA withdraws Sec.  23.700(c).
    Textron, ANAC, and Air Tractor commented that proposed Sec.
23.700(d) would require a takeoff warning system without explanation of
what it would be, and this could increase complexity.
    The FAA withdraws proposed Sec.  23.700(d) because the safety
requirement of warning a pilot who is attempting to takeoff with the
trim or flaps in an unsafe configuration is adequately addressed in
Sec.  23.2605(c).
b. Landing Gear Systems (Proposed Sec.  23.705/Now Sec.  23.2305)
    In the NPRM, proposed Sec.  23.705 (now Sec.  23.2305) would have
required--
     The landing gear and retracting mechanism be able to
withstand operational and flight loads;
     An airplane with retractable landing gear to have a
positive means to keep the landing gear extended and a secondary means
for extending the

landing gear that could not be extended using the primary means;
     A means to inform the pilot that each landing gear is
secured in the extended and retracted positions; and
     Airplanes, with retractable landing gear, except for
airplanes intended for operation on water, to also have a warning to
the pilot if the thrust and configuration is selected for landing and
yet the landing gear is not fully extended and locked.
    Furthermore, if the landing gear bay is used as the location for
equipment other than the landing gear, proposed Sec.  23.705 would have
required that equipment be designed and installed to avoid damage from
tire burst and from items that may enter the landing gear bay. Proposed
Sec.  23.705 would have also required the design of each landing gear
wheel, tire, and ski account for critical loads and would require a
reliable means of stopping the airplane with kinetic energy absorption
within the airplane's design specifications for landing. For level 3
high-speed multiengine and level 4 multiengine airplanes, proposed
Sec.  23.705 would have required the braking system to provide kinetic
energy absorption within the design of the airplane specifications for
rejected takeoff as the current rules do for multiengine jets over
6,000 pounds and commuter category airplanes.
    Several commenters argued that proposed Sec.  23.705 was too design
specific and recommended the FAA replace specific design elements such
as brakes, wheels, and tires with objectives that would work for a wide
array of technologies.
    In light of comments received, the FAA revises proposed Sec.
23.705 to withdraw proposed paragraphs (a)(1) through (d), to be
replaced with new paragraphs (a)(1), (a)(2), (b), (c)(1) and (c)(2).
This section discusses these changes in more detail.
    The FAA reassessed the need for the language of proposed Sec.
23.705(a)(1) and (b) and decided not to adopt the proposed paragraphs.
The FAA has determined these requirements are adequately addressed by
proposed Sec. Sec.  23.310 (now Sec.  23.2210), 23.320 (now Sec.
23.2220), and 23.400 (now Sec.  23.2235). Section 23.2210 requires
structural design loads to be determined that result from likely
externally or internally applied pressures, forces or moments, that may
occur in flight, ground and water operations, ground and water
handling, and while the airplane is parked or moored. This includes
operational and flight loads on the landing gear and retracting
mechanism, including the wheel well doors specified in the FAA's
proposed Sec.  23.705(a)(1). Section 23.2235 requires the structure to
support these loads. Section 23.2220 requires the applicant to
determine the structural design loads resulting from taxi, takeoff,
landing, and ground handling conditions occurring in normal and adverse
attitudes and configurations. This includes the critical loads on
wheels, tires, and skis specified in proposed Sec.  23.705(b). Section
23.2235 requires the structure to support these loads.
    Commenters noted proposed Sec.  23.705 diverged from EASA's
proposed CS 23.425, and recommended the FAA work with EASA to achieve
harmonization. Several commenters recommended the FAA reject the
language originally proposed for Sec.  23.705 and replace it with the
language from EASA's proposed CS 23.2325.
    The FAA agrees that it should harmonize Sec.  23.2305 as much as
possible with CS 23.2325, and has done so where appropriate.
    The Associations recommended the FAA revise proposed paragraph (a),
which would define landing gear. Textron recommended the FAA add a
requirement to provide stable support and control to the airplane
during ground operation. The commenters noted the change to paragraph
(a) would harmonize with EASA.
    The FAA finds the recommended language for paragraph (a)
unnecessary. The FAA also finds the accepted means of compliance will
describe what is considered landing gear for a particular airplane
design. The FAA notes the recommended language is overly broad and can
be read to encompass rudder systems and other systems that do not
directly interact with the ground, but are necessary to control the
airplane during surface operation. The FAA notes rudder systems and
other systems are adequately addressed elsewhere.
    The FAA revises Sec.  23.2305(a)(1) to adopt CS 23.2325(b)(1) by
requiring the landing gear to be designed to provide stable support and
control during surface operation. Although the NPRM did not
specifically address this requirement, the FAA intended for the revised
regulations to capture the safety intent of the former part 23
regulations. This also harmonizes with EASA.
    The FAA will not adopt the landing gear loads and energy absorption
requirements in CS 23.2325(b)(2) and (b)(3) because these requirements
are adequately addressed in Sec. Sec.  23.2210, 23.2220, and 23.2235.
The FAA notes the airplane has to be designed for the anticipated
loads, and energy absorbed by the landing gear affects the airframe
loads, which are addressed in these sections. Additionally, proper
function of any systems related to absorption of energy in the landing
gear is addressed in Sec.  23.2505.
    The FAA adopts CS 23.2325(b)(4) as Sec.  23.2305(a)(2), requiring
the landing gear to be designed to account for likely system failures
and likely operation environment, including anticipated limitation
exceedances and emergency procedures. As a result of this revision, the
FAA withdraws proposed Sec.  23.705(a)(3).
    Although the NTSB supported proposed Sec.  23.705(a)(3), the FAA
notes proposed Sec.  23.705(a)(3) only addressed tire failures on
airplanes with retractable landing gear based on the assumption that
tire burst and foreign object risk is greater on airplanes with
retractable landing gear. This is generally true for traditional
airplane designs. The risk is generally more severe on airplanes with
large numbers of passengers, flight critical systems near the landing
gear, complex systems, and high-speed operation on the ground. These
factors generally exist on airplanes with retractable landing gear, but
they could exist on airplanes with fixed landing gear. Conversely, the
risk is generally less severe on airplanes with no passengers, no
flight critical systems near the landing gear, simple systems and low-
speed operation on the ground. These factors generally exist on
airplanes with fixed landing gear, but they could exist on airplanes
with retractable landing gear (e.g., powered gliders). Therefore, the
proposed Sec.  23.705(a)(3) assumption that airplanes with retractable
landing gear should be protected from the risks of tire failures and
foreign objects, but airplanes with fixed landing gear should not be
protected, may not be correct for future designs.
    Section 23.2305(a)(2) applies to all landing gear and requires
landing gear failures to be considered more generally. The FAA finds
Sec.  23.2305(a)(2) will allow traditional designs to comply using
current practices as means of compliance, with the flexibility to
develop new means of compliance more appropriate for potential future
designs. This furthers the goal of moving to performance-based
requirements.
    The FAA notes Sec.  23.2305(a)(2) captures the intent of former
Sec. Sec.  23.721, 23.729, 23.735, and 23.1309, which required that
applicants account for likely landing gear failures. It also captures
the intent of former Sec. Sec.  23.603, 23.721, 23.729, 23.735,
23.1301, and 23.1309, which required that applicants account for likely
operation environments, and/or anticipated

limitation exceedances and emergency procedures.
    The commenters recommended that the FAA move the substance of
proposed Sec.  23.705(a) for airplanes with retractable landing gear to
proposed Sec.  23.705(c) and replace the proposed language with CS
23.2325(d), which deals with airplanes that have a system that actuates
the landing gear.
    The FAA has considered the comments and has decided to adopt CS
23.2325(d)(1) and (4) as Sec.  23.2305(c)(1) and (2). CS 23.2325(d)(1)
and (4) require a positive means to keep the landing gear in the
landing position and an alternative means available to bring the
landing gear in the landing position when a non[hyphen]deployed system
position would be hazardous. The FAA adopts Sec.  23.2305(c)(1) because
it is less prescriptive than proposed Sec.  23.705(a)(2)(i). The FAA
notes the recommended phrase ``in the landing position'' is less
prescriptive than ``extended'' and better expresses the intent of the