arbitrarily limiting an airplane's VMO and MMO
below the airplane's capabilities to avoid more stringent certification
standards. ANAC asked the FAA to elaborate on the connection between an
airplane's VMO and MMO and takeoff risk.
    The FAA does not agree that stall speed is the best parameter to
use for determining performance levels. Although an airplane's top
speed generally has been aerodynamically limited to a multiple of stall
speed that varied depending on propulsion, this is not true for all
airplanes and does not provide the necessary flexibility to address
airplanes that incorporate new technology. For example, there are
airplanes in development that have very low-stall speeds--the airplane
can land and takeoff in very little space, or even vertically--but may
have VNO or VMO greater than 250 KCAS, making
them a high-performance airplane.
Simple Airplane Classification
    The FAA proposed to define ``simple'' airplanes to recognize the
entry-level airplane. Simple airplanes would have been limited to
airplane designs that allow no more than one passenger, are limited to
VFR operations, and have a low top speed and a low stall speed.

The FAA asked for comments concerning the value of creating a simple
airplane sublevel given that a simple airplane would have
characteristics very similar to a certification level 1, low-speed
airplane.
    ICON, Transport Canada, BendixKing, NATCA, and two individual
commenters supported the inclusion of a separate ``simple'' airplane
classification. However, Zee and the Associations commented that the
FAA should not create a ``simple'' airplane classification, and that
each of the proposed certification and performance levels should stand
on its own based solely on performance and complexity of operations.
The commenters against inclusion of a ``simple'' category contended
that it was more appropriate to address this sort of classification in
the means of compliance.
    The FAA has decided not to adopt a ``simple'' airplane
classification. The FAA finds the addition of a simple category does
not produce benefits over those already provided by the new rule. The
FAA finds it is more appropriate to address the requirements for a
level 1, low-speed airplanes. Additionally, in the NPRM, the FAA
proposed allowing simple airplanes to use non-type-certificated engines
and propellers to allow those airplanes to use electric propulsion. The
FAA can achieve the same flexibility by approving electronic propulsion
as part of an airframe for a level 1, low-speed airplane; therefore,
the FAA revises the propulsion requirements in this rule to provide
that flexibility.
Airplanes Certified for Aerobatics
    The FAA proposed to eliminate the acrobatic airplane category in
part 23, but still allow a normal category airplane to be approved for
aerobatics provided the airplane was certified to address the factors
affecting safety for the defined limits for that kind of operation.
    Velica S.A.S. (Velica) recommended the FAA define ``aerobatic
category'' in proposed Sec.  23.5 to include airplanes without any
maneuver restrictions, other than those shown to be necessary as a
result of required flight tests.
    For the reasons explained in the NPRM, the FAA removed the
acrobatic category from part 23. The FAA agrees with Velica that the
limitations for an airplane certified for aerobatics should be based on
flight tests, but believes more specificity is warranted. Therefore,
the FAA will require airplanes certified for aerobatics to comply with
the limitations established under subpart G of part 23 in this rule.
c. Accepted Means of Compliance (Proposed Sec.  23.10/Now Sec.
23.2010)
    In the NPRM, proposed Sec.  23.10 (now Sec.  23.2010) would have
required an applicant to show the FAA how it would demonstrate
compliance with this part using a means of compliance, which may
include consensus standards accepted by the Administrator. Proposed
Sec.  23.10 would have also required a person requesting acceptance of
a means of compliance to provide the means of compliance to the FAA in
a form and manner specified by the Administrator. Proposed Sec.  23.10
would have created flexibility for applicants in developing means of
compliance and also specifically identify consensus standards as a
means of compliance the Administrator may find acceptable.
General Comments
    The Associations recommended the FAA revise paragraph (a) to
require an applicant to ``comply'' with part 23, rather than ``show the
FAA how it will demonstrate compliance'' with part 23, using a means of
compliance. The Associations also recommended revising paragraph (b) to
require an acceptable means of compliance to be in a form and manner
specified by the Administrator.
    The Associations also argued that, without these changes, the
proposed rule could have been interpreted as requiring each applicant
to come to agreement with the FAA on acceptable means of compliance for
each certification project, when it appears the FAA intends to issue
acceptance of methods of compliance in, for example, standards that are
already deemed acceptable. The commenters also noted that part 21 does
not currently require a showing of compliance in all cases. The
commenters stated that today, and potentially more so in the future,
the FAA may accept compliance through demonstration or even a statement
of compliance. The commenters contended the above-referenced revisions
to proposed Sec.  23.10 are necessary to ensure the designs meeting
part 23 can continue to fully utilize part 21.
    The FAA agrees with the commenters that proposed Sec.  23.10(a)
(now Sec.  23.2010(a)) may have had the unintended result of requiring
applicants to get approval from the FAA for each means of compliance
even when the FAA had already accepted a means of compliance. This
would have been counter to the FAA's intention that a means of
compliance, once accepted by the FAA, may be used for future
applications for certification unless formally rescinded. The FAA
adopts the commenters' recommendation for paragraph (a).
    The FAA does not adopt recommendation for paragraph (b) however,
because it would not meet the intent of the requirement. Paragraph (b)
addresses the situation in which an applicant proposes its own means of
compliance, either as an alternative to an accepted means of compliance
or as a new means of compliance for new technology. The FAA intended
paragraph (b) to require applicants requesting acceptance of a means of
compliance to do so in a form and manner specified by the FAA, not to
require already-accepted means of compliance to be documented in a form
and manner specified by the FAA. In light of the comment, the FAA
revises the proposed rule language to clarify that paragraph (b)
applies to applicants who are requesting FAA review and acceptance of a
proposed means of compliance.
    Air Tractor questioned the need for a new rule specifying that all
means of compliance must be accepted by the FAA and asked whether an
applicant would need to obtain FAA approval for each means of
compliance at the beginning of the process or any time prior to showing
compliance.
    This final rule is necessary because Congress directed the FAA to
issue a rule that replaces the prescriptive requirements of part 23
with performance-based regulations.\22\ This change means that
applicants for a TC may use any number of unique design elements to
attempt to comply with the performance-based requirements but only the
FAA can accept these as means of compliance because the FAA is
responsible for finding that an airplane satisfies the performance-
based requirements in part 23 before issuing a TC. Although the means
of compliance process is not new, the FAA adopts Sec.  23.2010 to make
the process clear to all applicants and to highlight that applicants
have the opportunity to develop alternative approaches to complying
with the part 23 performance-based requirements. While an applicant is
not required to obtain FAA acceptance of means of compliance at the
beginning of the certification process, it is advisable to seek
acceptance as soon as possible, or preferably before, to mitigate the
risk of having to redesign the airplane should the FAA not accept the
means of compliance.
---------------------------------------------------------------------------

    \22\ Small Airplane Revitalization Act of 2013 (Pub. L. 113-53,
49 U.S.C. 44704 note).
---------------------------------------------------------------------------

    NATCA commented the FAA should require the accepted means of

compliance be included on the published certification basis so products
can be standardized and post-TC modifiers can know the certification
basis used for the underlying product. NATCA also commented that
maintenance personnel returning an airplane back to service will need
access to adequate documentation on how an airplane is compliant with
the rule so they can verify the airplane remains compliant. Assuming
the standards are listed, NATCA asked the FAA to clarify how they would
be listed in the airplane certification basis.
    The FAA partially agrees with NATCA's concerns. Because many of the
detailed requirements are no longer in part 23 and will move to means
of compliance, it may be hard to know how an applicant showed
compliance. That said, many means of compliance today are proprietary,
and modifiers and maintenance personnel have no way of knowing what the
original manufacturer did to show compliance. The FAA is working with
its project support personnel to determine how much of the means of
compliance information needs to be listed on the FAA TCDS to address
concerns relating to post-TC modifiers and maintenance personnel. This
information will be included in the training currently being developed
for the ACO engineers and industry designees.
    NATCA also recommended the FAA permit design change applicants to
use their own alternate means of compliance to gain approval rather
than relying on the original means of compliance used for the
underlying TC. NATCA suggested this would be in line with the FAA's
statements that it is open to a means of compliance without preferring
one over the other.
    This option is currently permitted and will continue to be
permitted under the new part 23. Applicants requesting a change to type
design may propose their own means of compliance rather than using the
original means of compliance. However, the FAA will review the request
depending on the complexity of the design change or the alternative
means of compliance. While this is the current process, AC 23.2010
provides guidance on how to submit a proposed means of compliance to
part 23 for FAA acceptance.
    NATCA asked the FAA to clarify how the certification basis would be
handled for industry consensus standards. NATCA also asked whether an
applicant must at least partially use industry consensus standards, or
whether an applicant may choose not to use consensus standards at all.
Finally, NATCA asked if an applicant could get a part 23 TC by only
using the standards in ACs. Air Tractor suggested the FAA revise
proposed Sec.  23.10 to mention that the standards included in ACs are
an accepted means of compliance.
    The FAA notes that the certification basis will be the same as it
is today: Applicants must show compliance with part 23. An applicant
may choose not to use any consensus standards, or a combination of
consensus standards and other means of compliance, as long as the
applicant's proposed means of compliance complies with part 23 and is
accepted by the Administrator. The FAA finds it unnecessary to revise
the proposed rule language as Air Tractor suggested. An applicant may
already use ACs as means of compliance to part 23, where applicable,
under Sec.  23.2010.
Use of Applicant-Proposed Means of Compliance
    Air Tractor contended the use of applicant-proposed means of
compliance standards would lead to a significant loss in transparency
of the certification process, as individual applicants may choose to
make both the results and the process of showing compliance a matter of
proprietary intellectual property. ANAC commented that the FAA should
establish a method to publicize information about approved means of
compliance that are not part of a consensus standard. To preserve
proprietary information, ANAC recommended the FAA only publish
summaries as it currently does for exemptions, special conditions, and
ELOS findings. NATCA questioned how the FAA will handle proprietary
specifications within a certification basis, arguing it is not in the
public interest to have ``secret'' certification requirements. NATCA
recommended the certification basis be published in the Federal
Register for public comment. NATCA also recommended the certification
basis for proprietary information be ``explicitly identified'' on the
TCDS or STC. Finally, NATCA asked the FAA to clarify whether the FAA
will publish FAA issue papers when an applicant uses an applicant-
proposed means of compliance and, if so, noted that several FAA orders
and policies would need to be revised.
    The FAA has a responsibility to protect an applicant's proprietary
information, including a proprietary means of compliance. As such, the
FAA will not make the proprietary portions of applicant-proposed means
of compliance publicly available. The FAA plans to address applicant-
proposed means of compliance as it does today, by summarizing the
information. The FAA will identify the certification basis (i.e., the
applicable airworthiness standards) on the TCDS or STC as is done
today. The FAA has not published, and does not plan to publish, the
certification basis or FAA issue papers in the Federal Register for
public comment. Each applicant's certification basis is based on part
23 and is agreed to between the applicant and the FAA. The FAA is not
required to elicit public comment on proposed means of compliance.
    Garmin asked whether the FAA will accept portions of a previously
accepted means of compliance, or whether an applicant must use that
entire means of compliance. Garmin recommended the FAA revise proposed
Sec.  23.10 (now Sec.  23.2010) to permit whole or partial
implementation of a previously-accepted means of compliance or,
alternatively, ensure AC 23.10 permits this.
    The FAA agrees with Garmin and points out that this is acceptable
today. The FAA can be flexible in accepting mixed, partial, or entire
means of compliance from industry consensus standards as applicable to
the specific product. The FAA recognizes that new product innovations
will make this flexibility more important in the future. An industry
consensus standard can state that, for credit in meeting that standard,
the applicant has to meet the entire set of requirements. But the FAA
may tailor acceptable consensus standards based on what is appropriate
for the intended function.
Use of Current Part 23 as Means of Compliance
    Embraer recommended the FAA revise proposed Sec.  23.10(a) (now
Sec.  23.2010(a)) to acknowledge that an applicant may use the
prescriptive requirements in former part 23 as an alternate means of
compliance. Kestrel asked whether the FAA will require issue papers to
permit the use of these former prescriptive requirements.
    In the NPRM, the FAA noted it will accept the use of the
prescriptive means of compliance contained in former part 23 as
alternate means of compliance, except for those sections where the
level of safety has increased specifically for stall characteristics
and icing protection. The FAA does not need to codify this decision to
retain this flexibility and is therefore not revising the proposed
language for Sec.  23.10. For applicants relying on satisfaction of the
prescriptive requirements in former part 23, amendment 23-62, as a
means of compliance, the FAA will only require the G-1 certification
basis issue paper to list the means of compliance as ``amendment 23-
62''.

    NATCA asked whether the FAA will permit an applicant to use older
prescriptive regulations, such as Aeronautics Bulletin, amendment 7a,
``Airworthiness Requirements for Aircraft''; CAR 3; and previous
versions of part 23, as a means of compliance. If not, NATCA asked the
FAA to clarify why those regulations are not appropriate and acceptable
for the proposed design.
    The FAA will consider the use of the older, prescriptive
regulations in cases where it is appropriate for the airplane in
question. There have been instances where applicants have approached
the FAA with projects to ``remake'' new versions of vintage airplanes.
The FAA has allowed and will continue to allow the use of
appropriately-selected design standards on vintage airplanes. However,
applicants wanting to use this approach should expect to use newer
industry practices where the old standards and practices have, over
time, not proven to meet the minimum acceptable safety standard for
that class of airplane in part 23.
Manner in Which Applicant Must Present Means of Compliance
    Textron asked how the FAA will document the acceptance of a non-
industry standard means of compliance and whether acceptance of a
Project-Specific Certification Plan (PSCP) is adequate proof of the
FAA's acceptance of the means of compliance.
    The FAA plans to include information on the acceptance of non-
consensus standards on its Small Airplane Directorate Web site. The G-1
issue paper and agreement on the certification basis and compliance
checklist will suffice. PSCP acceptance is adequate proof of FAA
acceptance of a means of compliance if a G-1 issue paper is not used.
    Textron also asked whether there would be a system set-up similar
to repair specifications where an applicant could have pre-defined
methods for making certain changes to its products, and whether there
would be a method for the FAA to accept deviations to the accepted
standards.
    The Part 23 ARC did not consider and the NPRM did not propose
repair specification; therefore, it is beyond the scope of this
rulemaking effort.
    Air Tractor and Kestrel contended the process proposed by draft AC
23.10--which states that an applicant should list the means of
compliance and consensus standards they intend to use to show
compliance with part 23 in a certification plan or compliance
checklist--is premature and would slow the certification process. The
details of an airplane's design are often incomplete when an
application is submitted and it can take years to obtain FAA acceptance
of a PSCP. Air Tractor suggested that establishing a means of
compliance during the process of negotiating the PSCP should be limited
to picking one or more of the following: Analysis, tests, design
review, physical inspection, etc. Air Tractor also commented that a
requirement for the FAA to review and approve of particular methods
before the analysis can be presented would be new for most regulations.
It would also require a new level of required response from the FAA
that would drastically slow the process of either establishing the
certification plan or showing compliance. Air Tractor also questioned
how this requirement compares with the FAA and Industry Guide to
Product Certification.
    The FAA finds that including the means of compliance in the PSCP or
the compliance checklist will not alter the current practice for new
technology because some of the compliance requirements may not be known
at the time of application. This initial uncertainty means the agreed
compliance may remain as a draft during the development and
certification process until the specific means of compliance are
determined and agreed upon. This may be a common issue with new
technology during the first few years after the new part 23 is
implemented. It will take some time to get accepted means of compliance
into consensus standards, resulting in these means of compliance being
developed during the project. In the long term, the new approach should
shorten the time needed for an applicant to get FAA agreement on its
means of compliance.
    Finally, the FAA clarified the intent of the form and manner of the
means of compliance. The FAA does not intend to ``specify'' the form
and manner of means of compliance; the form and manner only need to be
``acceptable.''
3. Subpart B--Flight
a. Weight and Center of Gravity (Proposed Sec.  23.100/Now Sec.
23.2100)
    In the NPRM, proposed Sec.  23.100 (now Sec.  23.2100) would have
required an applicant to determine weights and centers of gravity that
provide limits for the safe operation of the airplane. Additionally, it
would have required an applicant to show compliance with each
requirement of this subpart at each combination of weight and center of
gravity within the airplane's range of loading conditions using
tolerances acceptable to the Administrator. Proposed Sec.  23.100 would
have also required the condition of the airplane at the time of
determining its empty weight and center of gravity be well defined and
easily repeatable.
    The Associations recommended a clarifying change to proposed Sec.
23.100(a) that would require the applicant to determine limits for
weights and centers of gravity that provide for the safe operation of
the airplane, rather than determine weights and centers of gravity that
provide limits.
    The FAA adopts the Associations clarifying change. Accordingly,
Sec.  23.2100(a) now requires the applicant to determine limits for
weights and centers of gravity that provide for the safe operation of
the airplane.
    Additionally, the Associations recommended changing proposed Sec.
23.100(b) to require the applicant to comply with each requirement of
subpart B at critical combinations of weight and center of gravity. The
commenters explained that it is appropriate to demonstrate compliance
at critical combinations of weight and center of gravity, but showing
compliance at each combination ``would present an infinite matrix of
test points.''
    The FAA also adopts the Associations recommended change to proposed
Sec.  23.100(b) (now Sec.  23.2100(b)). While proposed Sec.  23.100(b)
could have been interpreted to require an infinite matrix of test
points, this was not the FAA's intent. Accordingly, Sec.  23.2100(b)
now requires the applicant to comply with each requirement of subpart B
at critical combinations of weight and center of gravity within the
airplane's range of loading conditions using tolerances acceptable to
the Administrator.
    The Associations also stated that the determination of empty weight
and center of gravity in proposed Sec.  23.100(c) is ``somewhat
confusing and potentially unnecessary.'' The commenters suggested
clarifying changes that would replace ``empty weight'' with ``weight''
and delete ``well'' and ``easily repeatable,'' thereby requiring the
condition of the airplane at the time of determining its weight and
center of gravity to be defined. Similarly, Textron recommended
deleting the terms ``well'' and ``easily'' from proposed Sec.
23.100(c) because they are vague and subject to interpretation.
    The FAA is retaining the terms ``well defined'' and ``easily
repeatable'' in Sec.  23.2100(c). In the NPRM, the FAA explained
proposed Sec.  23.100 would capture the safety intent of Sec.  23.29.
Section 23.29 has contained the terms

``well defined'' and ``easily repeated'' since it was published in
amendment 23-0 \23\ with no challenges. Furthermore, ``easily'' is an
important modifier for ``repeatable'' because it ensures that the
condition of the airplane at the time of determining its empty weight
and center of gravity is not hard for a mechanic to reproduce.
---------------------------------------------------------------------------

    \23\ 29 FR 17955, December 18, 1964.
---------------------------------------------------------------------------

    The FAA also retains the term ``empty weight'' in Sec.  23.2100(c).
Determining empty weight is fundamental to baselining an airplane.
Removing this term would leave the weight value for baseline open to
any weight between empty to gross weight. The ambiguity of not defining
the baseline weight would create confusion and problems.
b. Performance Data (Proposed Sec.  23.105/Now Sec.  23.2105)
    In the NPRM, proposed Sec.  23.105 (now Sec.  23.2105) would have
required--
     An airplane to meet the performance requirements of this
subpart in various conditions based on the airplane's certification and
performance levels for which certification is requested;
     An applicant to develop the performance data required by
this subpart at various altitudes and at high temperatures, while also
accounting for losses due to atmospheric conditions, cooling needs, and
other demands on power sources; and
     The procedures used for determining takeoff and landing
distances to be executed consistently by pilots of average skill in
atmospheric conditions expected to be encountered in service.
    EASA and the Associations stated that some designs may have
performance limitations at low temperatures rather than high
temperatures, such as batteries in electric propulsion systems. The
commenters recommended revising the proposed language to require
performance data for low temperatures that can be expected during
operation, if those low temperatures could have a negative effect on
performance.
    The FAA agrees proposed Sec.  23.105(b) (now Sec.  23.2105(b))
should account for possible performance degradation due to the effect
of cold temperatures on electric propulsion systems. Proposed Sec.
23.105 was intended to capture the safety intent of former Sec.  23.45,
which required the determination of performance data in various
conditions that could negatively affect performance. Historically,
propulsion systems were gas powered and negatively affected by high
temperatures, which resulted in a corresponding negative effect on
performance. This explains why former Sec.  23.45 required the
determination of performance data at a temperature from standard to 30
degrees Celsius above standard, as performance degradations
historically resulted from operation at high temperatures.
    As stated in the NPRM, the FAA intended the proposal to account for
airplanes equipped with new technologies, such as electric propulsion
systems. Additionally, the FAA intended proposed Sec.  23.105(b) to
account for various conditions that could affect airplane performance.
However, proposed Sec.  23.105(b) would only have accounted for
performance degradations that could result from the operation of
systems at high temperatures, as the proposed language reflected former
Sec.  23.45. Because cold temperatures, rather than high temperatures,
may have a negative performance effect on an electric propulsion system
or a hybrid system, the FAA revises the proposed language to account
for performance degradations at low temperatures. The FAA also removes
the prescriptive language that would have required the determination of
performance data at a temperature from standard to 30 degrees Celsius.
    Section 23.2105(b)(2) now requires the applicant to develop
performance data at temperatures above and below standard day
temperature that are within the range of operating limitations, if
those temperatures could have a negative effect on performance. This
requirement is consistent with the NPRM as it replaces the prescriptive
design requirements from the regulation with performance-based
airworthiness standards that accommodate new technologies, such as
electric and hybrid propulsion systems. Additionally, Sec.
23.2105(b)(2) more accurately reflects the safety intent of former
Sec.  23.45 because it requires the development of performance data in
conditions that could negatively affect performance, including
conditions that account for new technologies.
    As a general matter, under Sec.  23.2105(b)(2), an applicant
seeking certification of a gas-powered propulsion system must develop
performance data at temperatures above standard that are within the
airplane's operating limitations, because high temperatures could have
a negative effect on the airplane's performance. Alternatively, an
applicant seeking certification of an electric or hybrid propulsion
system must develop performance data at temperatures both above and
below standard that are within the airplane's operating limitations, if
these temperatures could have a negative effect on performance.
    Garmin pointed out that limited airflow in a climb configuration
may cause non-propulsion systems to overheat during long hot climbs,
requiring a different climb speed or configuration for system cooling
than addressed in proposed Sec.  23.105(b). Garmin recommended the FAA
include the phrase ``other essential equipment'' in addition to
propulsion cooling in paragraph (b)(2).
    The Associations similarly suggested that there may be some cases
where the performance of equipment other than the propulsion system may
drive cooling requirements for hot conditions. The commenters
recommended revising the proposed language to include cooling
requirements for these equipment, in situations other than climb.
    The FAA understands the concerns of Garmin and the Associations,
for paragraph (b)(2) to address cooling requirements for more than the
propulsion system. However, subpart B--including Sec.  23.2105--is
intended to address airplane performance. Therefore, Sec.  23.2105
should only address systems that affect airplane performance. For
example, Sec.  23.2105 may apply to avionics that also control
propulsion, or flight controls and lift systems needed to develop
repeatable airplane performance. Traditional avionics that do not
affect performance are addressed in subpart F, which contains
requirements for equipment. Therefore, the FAA is not adopting the
phrase ``other essential equipment'' because it may be interpreted to
include systems that do not affect performance, such as oxygen or
navigation systems. This would be a new requirement that has not been
identified as a safety need, increasing the scope and possibly the cost
of this rule. For the same reasons, the FAA is not expanding the scope
of the rule to include cooling requirements for equipment other than
propulsion systems, in situations other than climb.
    Nevertheless, in light of the comments, the FAA acknowledges there
may be systems associated with propulsion that are necessary for
consistent performance, such as batteries or engine controllers, that
could be affected by temperature. Section 23.2105 should address these
types of systems. Therefore, Sec.  23.2105(b)(2) will apply to systems
associated with electric or other propulsion systems if those systems
could negatively affect performance at temperatures above or below
standard.

c. Stall Speed (Proposed Sec.  23.110/Now Sec.  23.2110)
    In the NPRM, proposed Sec.  23.110 (now Sec.  23.2110) would have
required an applicant to determine the airplane stall speed or the
minimum steady flight speed for each flight configuration used in
normal operations, accounting for the most adverse conditions for each
flight configuration, with power set at idle or zero thrust.
    The Associations recommended removing the proposed requirement for
power to be set at idle or zero thrust for each determination to enable
the introduction of new technologies such as distributed propulsion
with reliable electric power. The commenters explained that proposed
Sec.  23.110 must account for distributed lift systems because the
concept of distributed lift along a wing may be used to facilitate low-
speed handling, and reliable systems of this type may dictate
operational stall speeds. The commenters asserted their recommended
change would ensure that distributed propulsion, with an appropriate
reliability level, could be used in a landing condition accounting for
a lower stall speed based upon the effects of this equipment.
    The FAA agrees that proposed Sec.  23.110 (now Sec.  23.2110)
should account for distributed propulsion systems used for thrust,
flight controls, and high lift systems. However, the rule must define a
thrust level for standardization because stall speeds are important to
the development of the performance-based speeds. The FAA finds it
appropriate to require traditional designs to determine stall speeds
and minimum steady flight speeds with power set at idle or zero thrust.
Accordingly, Sec.  23.2110(a) now requires the power to be set at idle
or zero thrust for propulsion systems used primarily for thrust. To
accommodate distributed propulsion systems, the FAA is adding new Sec.
23.2110(b), which requires a nominal thrust for propulsion systems used
for thrust, flight control, and/or high-lift systems. These changes
will allow Sec.  23.2110 to accommodate the new technologies identified
by the commenters.
    Additionally, the FAA revises the proposed rule language to clarify
the ``stall speed or minimum steady flight speed determination'' must
account for the most adverse conditions for each flight configuration.
This change is consistent with the proposed rule, which would have
required ``each determination'' to account for the most adverse
conditions for each flight configuration, because ``each
determination'' referred to the ``stall speed or minimum steady flight
speed determination.''
d. Takeoff Performance (Proposed Sec.  23.115/Now Sec.  23.2115)
    In the NPRM, proposed Sec.  23.115 (now Sec.  23.2115) would have
required an applicant to determine airplane takeoff performance, which
would have included the determination of ground roll and initial climb
distance to 50 feet, accounting for stall speed safety margins, minimum
control speeds, and climb gradients. Proposed Sec.  23.115 would have
also required the takeoff performance determination to include
accelerate-stop, ground roll and initial climb to 50 feet, and net
takeoff flight path, after a sudden critical loss of thrust for levels
1, 2, and 3 high-speed multiengine airplanes, multiengine airplanes
with a maximum takeoff weight greater than 12,500 pounds, and level 4
multiengine airplanes.
    The Associations suggested the FAA revise proposed Sec.  23.115 to
capture the performance-based standards at a ``higher objective based
level'' because the proposed section was too detailed and prescriptive.
Textron recommended the FAA adopt language similar to EASA's A-NPA
2015-06, which leaves determination of detailed standards appropriate
to airplanes with different certification and performance levels to the
means of compliance standards.
    The FAA disagrees with the comment, because it is important to
ensure the consistency of takeoff performance data across part 23
airplanes. This consistency aids private pilots, who often operate a
variety of part 23 airplanes, in determining the airports from which
they may operate.
    Several commenters recommended the FAA remove the 12,500-pound
cutoff in proposed Sec.  23.115(c).
    The FAA agrees and removes the weight discriminator from the rule
language. Although the FAA proposed to remove the commuter category,
along with weight- and propulsion-based certification divisions, and to
replace them with divisions based on risk and performance, the FAA also
proposed to require multiengine airplanes with a maximum takeoff weight
of more than 12,500 pounds to comply with the increased takeoff
performance requirements in paragraph (c). Proposed paragraph (c) was
intended to ensure that larger business jets carrying fewer than 10
passengers, which would have been considered commuter category under
the former rule, were captured under the takeoff performance
requirements because these airplanes would not necessarily fall under
level 4. The FAA recognizes that applying paragraph (c) to multiengine
airplanes with a maximum takeoff weight of more than 12,500 pounds is
redundant. Those airplanes, which are equivalent to airplanes under the
former commuter category, are captured by applying paragraph (c) to
levels 1, 2, and 3 high-speed multiengine airplanes and to all level 4,
multiengine airplanes. Furthermore, while paragraph (c) does not apply
to levels 1, 2 and 3 low-speed multiengine airplanes, the FAA may issue
special conditions if there is a configuration that presents a higher-
than-anticipated risk.
    Several commenters objected to requiring the determination of
takeoff performance for all airplanes to include the determination of
initial climb distance to 50 feet above the takeoff surface. The
commenters noted that under the former rule, takeoff distance for
commuter category airplanes and multiengine jets weighing more than
6,000 pounds required the initial climb distance be calculated using 35
feet above the takeoff surface. Textron recommended the FAA revise
proposed Sec.  23.115(b) to apply the 50-feet-above-takeoff-surface
requirement only to single-engine airplanes and levels 1, 2, and 3 low-
speed multiengine airplanes rather than to all airplanes. Textron also
recommended revising proposed Sec.  23.115(c)(2) from ``50 feet'' to
``35 feet'' above the takeoff surface, noting the 35-foot standard has
been demonstrated as safe for the classes of airplane to which it has
been applied.
    The FAA agrees with the commenters and revises proposed Sec.
23.115(b) (now Sec.  23.2115(b)) to require only single-engine
airplanes and levels 1, 2, and 3 low-speed, multiengine airplanes to
include the distance required to climb to a height above 50 feet when
calculating takeoff performance. The FAA is also changing the altitude
for the initial climb in Sec.  23.2115(c)(2) to 35 feet. The service
history of airplanes that would be classified as levels 1, 2, and 3
high-speed multiengine airplanes and level 4 multiengine airplanes
under this rule, which were certified using a 35-feet-initial-climb
requirement, has been sufficiently safe to support the proposition that
the 35-feet requirement provides an adequate level of safety for high-
speed multiengine airplanes and level 4 airplanes.
    The Associations suggested revising proposed Sec.  23.115(b) and
(c) to require takeoff performance to include the determination of
``ground roll distance required to takeoff,'' rather than ``ground
roll.''
    The FAA notes using ``ground roll distance required to takeoff'' is
not necessary for clarity. The term ``ground

roll'' in the context of takeoff is well-understood.
    Several commenters recommended revising proposed Sec.  23.115(b) to
include two subparagraphs in what the FAA interprets as an effort to
clarify that the applicant must provide two distances, one for ground
roll and another for the distance required for the initial climb to 50
feet.
    The FAA finds it unnecessary to reorganize paragraph (b) as the
commenters proposed. The format, as proposed and adopted, is
sufficiently clear.
    The Associations suggested the FAA revise the proposed rule
language in proposed Sec.  23.115(c)(1) to require the takeoff
performance determination to include the distance determination of ``an
aborted take-off at critical speed,'' rather than ``accelerate-stop.''
    The FAA agrees that ``accelerate-stop'' is not as clear a
description of the objective of the maneuver as ``aborted take-off at
critical speed''. Therefore, the FAA revises paragraph Sec.
23.2115(c)(1) to reflect the commenters' recommendation.
    Embraer recommended the FAA provide special consideration--
including freezing the certification bases--for previously-approved
light jets with certification bases that include special conditions
measuring the takeoff distance as the distance required to takeoff and
climb to a height of 35 feet above the takeoff surface. Embraer feared
the potential cost associated with an upgrade or modification.
    The FAA finds a special consideration unnecessary. There is already
a process, prescribed by Sec.  21.101(b), that allows applicants for a
change to a TC to show that the change complies with an earlier
amendment of a regulation if the newer requirement would not contribute
materially to the level of safety of the product or would be
impractical.
    ANAC recommended the FAA make it clear that takeoff airspeed and
procedures must be determined. The FAA disagrees with ANAC's comment as
such a change would be redundant with what we proposed for Sec.  23.105
(now Sec.  23.2105).
e. Climb Requirements (Proposed Sec.  23.120/Now Sec.  23.2120)
    In the NPRM, proposed Sec.  23.120 (now Sec.  23.2120) would have
required an applicant to demonstrate various minimum climb performances
out of ground effect, depending on the airplane's certification level
and performance capability.
    In light of comments received, the FAA revises proposed Sec.
23.120 (now Sec.  23.2120) by withdrawing paragraphs (b)(4), (b)(5),
and (c)(1), and renumbering paragraphs (c)(2) and (c)(3) as (c)(1) and
(c)(2) respectively. This section discusses these changes in more
detail.
    Textron commented that regulations have historically applied to the
airplane, not to the applicant, with demonstration of compliance
through flight testing. Textron recommended the FAA offer alternative
rule language that reflected its comment. The Associations similarly
recommended the FAA change the opening of proposed Sec.  23.120 to
focus on the design rather than the applicant. These commenters also
recommended re-designating the opening as paragraph (a).
    The FAA notes that, historically, the airplane-specific
requirements focused on the airplane, and the part 21 certification
requirements were targeted more to the applicant. Many sections in this
rulemaking effort tried to include applicant accountability, which was
why the proposed rule focused on the ``applicant.'' However, based on
the comments received, the FAA revises the proposed language throughout
this rule by removing ``applicant'' where the requirement is more
logically based on the airplane.
    Textron commented on the proposal to apply discriminators based on
weight divisions and detailed quantitative climb criteria conflicted
with the stated intent of the rulemaking to remove weight-based
divisions and develop standards reflecting the diversity of future
airplane designs. Textron recommended the FAA adopt language similar to
proposed CS 23.120, which leaves determination of detailed standards
appropriate to airplanes with different certification and performance
levels to means of compliance. The Associations recommended the FAA
make the calculation of performances more general, to facilitate the
use of standard means of compliance, which may exist in consensus-based
standards. An individual commenter similarly stated the
prescriptiveness of proposed Sec.  23.120 was contrary to the stated
objective of the proposal. The commenter stated the text of proposed
Sec.  23.120 would be more appropriate as a standard rather than a
rule. The commenter recommended that the FAA use the language of
proposed Sec.  23.125, which would have required the determination of
climb performance in certain conditions and configuration, in proposed
Sec.  23.120. The commenter also noted the current version of the ASTM
standard for climb requirements already fully covers the language of
proposed Sec.  23.120.
    In response to Textron's comment, the FAA revises proposed Sec.
23.120 so it no longer contains weight divisions. Instead, the
requirements of this section are based on certification levels,
performance levels, and number of engines. Section 23.2120 does,
however, contain quantitative climb criteria. On this topic, the FAA
did not adopt the EASA proposed CS 23.120 language as recommended by
Textron. While the idea of removing all climb gradient requirements was
discussed in the Part 23 ARC, the FAA finds it is not in the best
interest of safety to eliminate all required climb gradients.
Therefore, the FAA is including the minimum climb gradients in this
performance-based rule. But, the FAA consolidated the climb gradient
requirements of former part 23 to simplify the requirement. The FAA
finds doing so will maintain the former level of safety while reducing
the certification burden. The FAA acknowledges the ASTM means of
compliance contain the climb gradients in more detail than required
from the requirements of this section. However, the ASTM means of
compliance has not been accepted by the FAA as of the publication of
this rule.
    The FAA finds that, while removing as many prescriptive
requirements as possible is important for creating a performance-based
rule, some requirements should remain because they have been proven
over decades of service and are already based on performance. The FAA
finds the climb requirements are one such case.
    In response to the comment that the FAA should use the language of
proposed Sec.  23.125 (now Sec.  23.2125) in proposed Sec.  23.120 (now
Sec.  23.2120), the FAA notes that Sec.  23.2125 only requires the
performance information be determined for the airplane flight manual
(AFM). There is no minimum climb gradient in Sec.  23.2125 as with
Sec.  23.2120. The Part 23 ARC discussed this issue at length with the
objective of defining a clear, minimum performance-based metric that
would allow the prescriptive climb gradients to move to means of
compliance. The climb gradients in former Sec. Sec.  23.65 through
23.77 came from early CAR 3 and have been in place for more than half a
century, with the exception of some commuter category requirements,
which came from early part 25. Since the FAA has established
measureable gradients, any alternative approach would need to maintain
the same gradients to provide an equivalent level of safety as the
former climb requirements. The ARC considered numerous options, but in
every case the proposed metric was subjective such that the FAA may be

required to evaluate various other climb gradient schemes against the
former climb gradients, when the intent was to maintain the former
climb gradients. Finally, the FAA determined keeping the prescriptive
climb gradients from the former rules remains the best approach.
Furthermore, supporting this position, the FAA could not envision new
and novel configurations that could not meet these climb gradients, but
would offer the same level of safety. All the new and novel
configurations that have been shared with the FAA have performance that
will meet or exceed the minimum gradients proposed in the NPRM. For
these reasons the FAA is retaining the proposed language.
    Furthermore, it may not have been clear in the NPRM that the FAA
intended proposed Sec.  23.120 to address the required minimum climb
gradients in former Sec. Sec.  23.63, 23.65, 23.67, and 23.77, and
proposed Sec.  23.125 (now Sec.  23.2125) to address the required
publication of the measured performance in former Sec. Sec.  23.66,
23.69, and 23.71. Therefore, the FAA is not including language similar
to proposed Sec.  23.125 (now Sec.  23.2125) in Sec.  23.2120, because
Sec.  23.2120 includes required climb gradients, not information
requirements.
    Textron stated that proposed Sec.  23.120(a) would have applied to
the all engines operating (AEO) takeoff climb and that a common
terminology should be used. Textron recommended the FAA replace the
undefined phrase ``initial climb configuration'' in proposed paragraph
(a) with the unambiguous phrase ``takeoff configuration'', and remove
the phrase ``at takeoff'' from proposed paragraph (a)(2). Textron also
recommended the FAA remove the phrase ``at sea level'' from proposed
paragraph (a)(1) because the FAA already proposed Sec.  23.105 to
require an airplane, unless otherwise prescribed, to meet the
performance requirements of this subpart in still air and standard
atmospheric conditions at sea level for all airplanes.
    The FAA notes that replacing ``initial climb configuration'' with
``takeoff configuration'' would require the design to comply with the
required minimum climb performance out of ground effect, with all
engines operating and in the ``takeoff configuration''. The FAA finds
that this change would be more stringent than the former regulations.
Former Sec.  23.65(a) allowed for the climb to be demonstrated with the
landing gear retracted, and former Sec.  23.65(b) allowed for the climb
to be demonstrated with the landing gear retracted if it could be
retracted in 7 seconds. While normalizing both former regulations might
appear relieving for airplanes certified as complying with former Sec.
23.65(b),\24\ the FAA finds that most airplanes designed in the past 2
decades incorporated landing gear that retracted in less than seven
seconds. Therefore, the FAA is retaining the phrase ``initial climb
configuration'' in paragraph (a).
---------------------------------------------------------------------------

    \24\ Former Sec.  23.65(b) applied to normal, utility, and
acrobatic category reciprocating engine-powered airplane of more
than 6,000 pounds maximum weight, single-engine turbine, and
multiengine turbine airplanes of 6,000 pounds or less maximum weight
in the normal, utility, and acrobatic category.
---------------------------------------------------------------------------

    The FAA agrees with Textron's recommendation to delete ``at sea
level'' from proposed Sec.  23.120(a)(1). The FAA proposed the term
because it was part of former Sec.  23.65(a). As Textron noted,
however, proposed Sec.  23.105(a) (now Sec.  23.2105(a)) would have
already required an airplane to meet the performance data of subpart B,
including Sec.  23.2120, in still air and atmospheric conditions at sea
level for all airplanes. It is therefore unnecessary for paragraph
(a)(1) to require a climb gradient ``at sea level'' of 8.3 percent for
landplanes and 6.7 percent for seaplanes and amphibians. However, the
FAA is not deleting ``at takeoff'' as recommended by Textron. The
agency is aligning the new rule with former Sec.  23.65 by using
``after takeoff'' instead of ``at takeoff.'' This requirement is
indirectly addressed in Sec.  23.2105(b); however, as proposed, the
language was not clear as to intent. By including the term ``after
takeoff'', this requirement reinforces the meaning of ``ambient
atmospheric conditions'' in Sec.  23.2105(b).
    The Associations and Transport Canada noted that proposed Sec.
23.120(a) did not address climb performance for level 4 airplanes.
Transport Canada stated the FAA should specify all engine operating
climb gradient requirements for level 4 airplanes. The Associations
stated the climb gradient requirements for level 4 airplanes should be
the same as the requirement for high-speed level 1 and 2 airplanes and
level 3 airplanes.
    The FAA considered the comments and in response, revises proposed
Sec.  23.120(a) to include an all engines operating climb requirement
for level 4 single-engine airplanes. The former climb requirements
required all airplanes with 10 or more passengers to have multiple
engines and meet the commuter category climb requirements, which were
focused on the ability to climb after an engine failure. These one-
engine-inoperative climb requirements were extensive. The philosophy
was that if the airplane could meet the climb requirements after one
engine failed, it would have more-than-adequate performance with all
engines operating. This is why there were no all engine operating climb
requirements for commuter category airplanes. The FAA agrees with and
continues this philosophy in the new rule for multiengine airplanes
designed for 10 or more passengers, which are level 4 airplanes under
this rule. However, because the new rule eliminates the commuter
category and allows for single-engine airplanes to carry 10 or more
passengers, there is now a need for single-engine level 4 airplanes to
have an all engines operating climb requirement.
    The FAA agrees with the Associations that the climb gradient
requirements for level 4 single-engines airplanes should be the same as
the requirement for levels 1 and 2 high-speed airplanes and level 3
airplanes. This was an oversight in the NPRM and the FAA is correcting
it in this final rule. Accordingly, Sec.  23.2120(a)(2) now requires
levels 1 and 2 high-speed airplanes, all level 3 airplanes, and level 4
single-engine airplanes to demonstrate, with all engines operating and
in the initial climb configuration, a climb gradient at takeoff of 4
percent. This revision is a logical outgrowth of the notice because, as
noted by the commenters, there is no basis for distinguishing between
level 3 and level 4 airplanes for this requirement.
    Transport Canada commented that the FAA should consider and
validate whether a 4 percent climb gradient for high-performance
airplanes with all engines operating is sufficient. For example, an
airplane climbing at 100 knots (approximately 400 feet per minute) may
be acceptable for a level 1 airplane, but not for anything larger.
Transport Canada noted that proposed paragraph (a)(2) may govern more
frequently, because the all-engine climb capability driven by the one-
engine-inoperative requirements has been reduced in proposed paragraph
(b)(3). Transport Canada also noted that, given the increasing
probability of airplanes with more than 4 engines, it may be more
effective to increase the all-engine climb gradient in proposed
paragraph (a)(2).
    The FAA considered Transport Canada's comments, but notes the
intent with this section was to maintain the level of safety in former
part 23. Section 23.2120(b) requires the same climb gradient--4
percent--as was required for similar airplanes by former part 23. The
FAA notes that requiring more stringent climb requirements is beyond
the scope of this rulemaking.

    Textron made several comments to proposed Sec.  23.120(b). Textron
stated the word ``the'' should replace the word ``a'' when referring to
critical loss of thrust. For proposed Sec.  23.120(b)(1), Textron
suggested referring to climb gradient the same way as in proposed Sec.
23.120(a)(2). Textron also recommended changing ``configuration'' to
``configurations'' in proposed paragraph (b)(1) because one airplane
may have multiple takeoff and approach configurations. Textron and
Kestrel requested clarification regarding the single-engine
crashworthiness requirements referred to in proposed Sec.
23.120(b)(1). Kestrel asked whether those requirements will be
established in the rule or based on an associated standard.
    Regarding Textron's comment on the use of the word ``the'' in the
phrase ``the critical loss of thrust,'' the term ``the'' would assume
that everyone knows what that critical loss of thrust is. While that
may be true for traditional configurations, it may not be true for
future configurations. Therefore, the FAA is keeping the proposed
phrase ``a critical loss of thrust.'' However, the FAA agrees with
Textron concerning multiple configurations and revises the rule to
align the reference to the climb gradient in Sec. Sec.  23.2120(a)(2)
and 23.2120(b)(1) for clarity.
    In response to Kestrel and Textron, Sec.  23.2120(b)(1) contains a
requirement addressing airplanes that do not meet the single-engine
crashworthiness requirements of proposed Sec.  23.600, ``Emergency
conditions'' (now Sec.  23.2270). Section 23.2120(b)(1) is intended to
capture the intent of former Sec.  23.67(a)(1), which required
airplanes with VSO of more than 61 knots to maintain a
steady climb gradient of at least 1.5 percent. Sixty-one knots was a
historic stall speed limit for single-engine airplanes and for that
reason, it was used as a division between multiengine airplanes that
could climb after the loss of one engine and other multiengine
airplanes that could not maintain altitude after the loss of one
engine. These former requirements assumed that the airplane only had
two engines. The FAA is not using the 61 knot stall speed division in
this new rule the way it was used in former Sec.  23.562, ``Emergency
landing dynamic conditions'', for crashworthiness requirements.
Instead, the FAA is basing these new regulations on actual stall speed.
The new regulations should, over time, allow several alternatives to
address occupant protection. For this reason, and because the FAA did
not intend to increase the level of safety over the former
requirements, the FAA is using the phrase ``single-engine
crashworthiness.''
    Textron asserted that to obtain the best takeoff performance in
high and hot conditions, it can be advantageous to use lesser flap
settings to improve climb capability after takeoff. However, the
proposed climb requirements--defined only in terms of the approach
configuration--would have eliminated this capability, and would not
have reflected the former part 23 standards. Textron suggested the FAA
revise the proposed rule language in paragraph (b)(3) to require
multiengine level 3 high-speed airplanes and level 4 airplanes to
determine the climb gradients for weight, altitude, and temperature
combinations appropriate for takeoff in the takeoff configuration.
    The FAA notes that the reason for using the ``approach
configuration'' was not that it reflected an actual configuration, but
that it was more conservative than using the ``takeoff configuration.''
The FAA elected to consolidate the climb requirements from four
configurations into one configuration. To do so, the FAA had to make
some assumptions. The major assumption used in consolidating the climb
requirements was that if the airplane could meet the second segment
climb gradient at 400 feet, then it should meet the other traditional
requirements and would provide an acceptable level of safety. However,
to provide a margin of safety in case one of the other conditions was
slightly more critical, the FAA elected to apply the discontinued
approach flap configuration, which is ``approach'' flaps, for this
requirement.
    Transport Canada commented it would be more conservative to require
the four-engine climb gradient of 2.6 percent in proposed Sec.
23.120(b)(3), rather than the two-engine climb gradient of 2 percent.
    The FAA explained in the NPRM that the climb gradient associated
with the loss of one engine for a two-engine airplane has provided an
acceptable safety history for this class of airplane. The historical
three- and four-engine climb gradients were based on part 25
regulations regarding gas engine technology, and may not be appropriate
for distributed electric propulsion configurations or designs. For this
reason, using those historical values may end up with a more
conservative approach than intended. This would increase the
requirements from the former part 23 regulations, which is outside the
scope of this rulemaking.
    Several commenters recommended the FAA either delete, clarify, or
re-write proposed Sec.  23.120(b)(4) and (5) because the intent of
those paragraphs is unclear.
    The FAA agrees that proposed Sec.  23.120(b)(4) and (b)(5) are
confusing. The FAA intended the conditions in paragraphs (b)(4) and
(b)(5) to apply to the determinations required by paragraph (b).
However, because Sec.  23.2105(a) requires an airplane to meet the
performance data of subpart B for these 2 conditions, paragraphs (b)(4)
and (b)(5) are redundant and confusing. For this reason, the FAA
withdraws paragraphs (b)(4) and (b)(5).
    An individual commented that all multiengine airplanes should be
able to climb after an engine failure. The commenter stated this
performance is affordable and the FAA should not permit poor
performance because a manufacturer wants to refurbish a decades-old
design and produce it.
    The FAA notes that adding the requirement for all-multiengine
airplanes to be able to climb after an engine failure is beyond the
scope of this rulemaking. The FAA finds that the current level of
safety in former part 23 regarding climb performance for multiengine
airplanes following an engine failure is adequate.
    The Associations recommended the FAA revise the proposed rule
language to require the applicant to demonstrate a climb gradient of 3
percent during balked landing ``without creating undue pilot
workload.'' The commenters also recommended the FAA rewrite proposed
Sec.  23.120(c) to include a general requirement for the applicant to
determine, as applicable, climb and descent performance for all engines
operating; following a critical loss of thrust on take-off; and after a
critical loss of thrust during the enroute phase of flight.
    The FAA originally determined that adding the phrase ``without
creating undue pilot workload'' in this requirement was redundant with
proposed Sec.  23.105(c); however, proposed Sec.  23.105(c) only
addressed takeoff and landing distances. The FAA also recognizes that
many of the part 23 fatal accidents happen on go-arounds or balked
landings and are attributable, at least in part, to high-pilot
workload. For this reason, the FAA is adding ``without creating undue
pilot workload'' to Sec.  23.2120(c).
    The FAA also addresses the commenters' recommendation to include a
general requirement for the applicant to determine, as applicable,
climb and descent performance for all engines operating; following a
critical loss of thrust on take-off; and after a critical loss of
thrust during the enroute

phase of flight in Sec.  23.2125(a)(2) and (a)(3).
    Textron and Transport Canada also commented on proposed Sec.
23.120(c). Textron stated that it is unclear why takeoff power is
specified for the balked landing, but not for any other minimum climb
performance requirements. Textron recommended changing the word
``configuration'' to ``configurations'' in proposed Sec.  23.120(c)(3)
because an airplane might have multiple landing configurations.
    The FAA agrees with Textron that the reference to takeoff power was
not needed. Therefore, the FAA deletes the reference from proposed
Sec.  23.120(c) (now Sec.  23.2120(c)). The FAA also agrees with
Textron's recommendation to change ``configuration'' to
``configurations'' and makes this change in Sec.  23.2120(c).
    Transport Canada asked that the FAA justify the reduction in the
required landing climb gradients from 3.3 percent to 3 percent.
    The FAA notes that former Sec.  23.77, which governed balked
landings, required a 3.3 percent gradient for piston airplanes weighing
less than 6,000 pounds; a 2.5 percent gradient for piston engine and
single-engine turbine-powered airplanes over 6,000 pounds and for
multiengine turbine-powered airplanes weighing 6,000 pounds or less;
and a 3.2 percent gradient for multiengine turbine-powered airplanes
weighing over 6,000 pounds and commuter category airplanes. The FAA is
simplifying the former requirement by taking the average of the three
climb gradients. The FAA did not receive any negative comments
concerning the decrease or increase in climb gradient requirements, so
the FAA adopts the language as proposed.
f. Climb Information (Proposed Sec.  23.125/Now Sec.  23.2125)
    In the NPRM, proposed Sec.  23.125 (now Sec.  23.2125) would have
required an applicant to determine the climb performance for--
     All single-engine airplanes;
     Level 3 multiengine airplanes, after a critical loss of
thrust on takeoff in the initial climb configuration; and
     All multiengine airplanes, during the enroute phase of
flight with all engines operating and after a critical loss of thrust
in the cruise configuration.
    Proposed Sec.  23.125 would have also required an applicant to
determine the glide performance of the airplane after a complete loss
of thrust for single-engine airplanes.
    Transport Canada commented that proposed Sec.  23.125(a) appears to
lack the concept of determining climb performance at each approved
weight, altitude, and temperature. Additionally, Transport Canada
stated it is unclear why proposed Sec.  23.125(a)(2) applies only to
level 3 multiengine airplane. Transport Canada recommended the FAA
require the determination of climb performance following a critical
loss of thrust on take-off in the initial climb configuration for all
multiengine airplanes at each weight, altitude, and temperature.
    The FAA agrees with Transport Canada that proposed Sec.  23.125(a)
would not have expressly required the determination of climb
performance at each approved weight, altitude, and temperature. The FAA
intended proposed Sec.  23.105(a)--which would have required levels 1
and 2 high-speed airplanes and level 3 airplanes to provide performance
data in ambient atmospheric conditions within the operating envelope--
to capture this requirement. To comply with the requirement in proposed
Sec.  23.105(a) to ``meet the performance requirements'' of subpart B,
an applicant would have had to make these determinations anyway.
However, after considering Transport Canada's comment, the FAA revises
the proposed language to make clear that Sec.  23.125(a)(2) (now Sec.
23.2125(a)(2)) requires the determination of climb performance at each
weight, altitude, and ambient temperature within the operating
limitations. This change is consistent with the NPRM, which explained
that proposed Sec.  23.125 was intended to capture the safety intent of
former Sec. Sec.  23.66 and 23.69. Both of these sections required the
determination to be made at each weight, altitude, and ambient
temperature within the airplane operating limitations.
    The FAA agrees that Sec.  23.2125(a)(2) should apply to more than
level 3 multiengine airplanes; however, it should not apply to all
multiengine airplanes. Section 23.2125(a)(2) captures the safety intent
of former Sec.  23.66, which applied only to reciprocating engine-
powered airplanes of more than 6,000 pounds maximum weight and turbine
engine-powered airplanes. Under the new performance-based regulations,
the equivalent airplanes--considering the intent of former Sec.
23.66--are levels 1 and 2 high-speed multiengine airplanes and all
level 3 airplanes. Therefore, the FAA revises the proposed rule
language to include levels 1 and 2 high-speed multiengine airplanes in
addition to level 3 multiengine airplanes, to maintain the same level
of safety as former Sec.  23.66. However, because former Sec.  23.66
did not apply to commuter-category airplanes--which were considered the
equivalent of level 4 multiengine airplanes--Sec.  23.2125(a)(2) should
not apply to all multiengine airplanes as doing so would make the rule
more stringent than former Sec.  23.66.
    Textron noted the continuous reference to ``a critical loss of
thrust'' in proposed Sec.  23.125 and recommended the FAA refer to it
as ``the critical loss of thrust.'' The FAA understands Textron's
comment; however, the term ``the critical loss of thrust'' assumes
there is a critical loss of thrust and that it is a known, finite
condition for all multiengine airplanes. This may not be the case. The
phrase ``a critical loss of thrust'' allows for the possibility that
there is no critical loss of thrust or that different airplane
configurations would have different critical loss of thrust conditions
based on a specific configuration.
    Textron recommended deleting the undefined phrase ``initial climb
configuration'' from proposed Sec.  23.125. Textron also recommended
the FAA not require multiengine airplanes to be in the cruise
configuration during the determination of climb performance in the
enroute phase of flight. Textron explained that while the enroute phase
of flight is typically associated with a ``clean'' airplane
configuration, the applicant should be free to define this
configuration.
    The FAA agrees with Textron's intent, but does not accept Textron's
recommendations. The FAA is requiring the airplane to be in the
``initial climb configuration'' in Sec.  23.2125(a)(2) and the ``cruise
configuration'' in Sec.  23.2125(a)(3). However, the FAA is not
defining ``initial climb configuration'' because a definition would be
prescriptive and inflexible for new configurations, which would be
contrary to this performance-based regulation. Paragraphs (a)(2) and
(a)(3) capture the safety intent of former Sec. Sec.  23.66 and 23.69,
respectively. Former Sec. Sec.  23.66 and 23.69 contained prescriptive
requirements pertaining to the takeoff and enroute configurations,
which were based on airplane designs over the past half-century. The
FAA finds the new rules should include traditional configurations, but
be flexible enough for new configurations in the future. These new
configurations may be different from what was traditionally required in
part 23 due to a unique propulsion, high lift, and/or flight control
configuration. Therefore, Sec.  23.2125(a)(2) and (a)(3) specify the
configuration conditions in a performance-based manner that allows
flexibility for the applicant to define what the configuration is in
means of compliance.

    Furthermore, based on another comment from Textron, the FAA deletes
unnecessary text in paragraph (b) and moves the phrase ``single engine
airplanes'' in the same paragraph to make the rule language of Sec.
23.2125(b) read consistently with Sec.  23.2125(a).
g. Landing (Proposed Sec.  23.130/Now Sec.  23.2130)
    In the NPRM, proposed Sec.  23.130 (now Sec.  23.2130) would have
required an applicant to determine the landing distance for standard
temperatures at each weight and altitude within the operational limits
for landing. The landing distance determination would start from a
height of 50 feet (15 meters) above the landing surface, require the
airplane to land and come to a stop (or for water operations, reach a
speed of 3 knots) using approach and landing speeds, configurations,
and procedures which allow a pilot of average skill to meet the landing
distance consistently and without causing damage or injury. Proposed
Sec.  23.130 would have required these determinations for standard
temperatures at each weight and altitude within the operational limits
for landing.
    Transport Canada stated proposed Sec.  23.130 should require the
landing performance to account for stall speed safety margins and
minimum control speeds to maintain consistency with the take-off
requirements in proposed Sec.  23.115 (now Sec.  23.2115) and to ensure
the same level of safety as former part 23.
    The FAA agrees the landing requirements of proposed Sec.  23.130
(now Sec.  23.2130) should expressly account for stall speed safety
margins and minimum control speeds consistent with the takeoff
performance requirements of proposed Sec.  23.115 (now Sec.  23.2115).
Proposed Sec.  23.130(b) would have generally required the
determination of approach and landing speeds. As explained in the NPRM,
the FAA intended proposed Sec.  23.130 to capture the safety intent of
former Sec.  23.73, which required the reference landing approach speed
to account for minimum control speed (VMC) and
VS1. The FAA's intention to account for stall speed safety
margins and minimum control speed, which would ensure the same level of
safety as former Sec.  23.73, was not clear in the proposed rule
language. Accordingly, the FAA is adding language to paragraph Sec.
23.2115(b) to clarify that an applicant must account for stall speed
safety margins and minimum control speeds when determining the approach
and landing speeds, configurations, and procedures.
    Several commenters recommended clarifying changes to proposed Sec.
23.130. The Associations recommended deleting the phrases ``the
following'' and ``for landing'' in the introductory paragraph. Textron
recommended various changes to proposed Sec.  23.130(b), such as
replacing ``meet'' with ``achieve,'' specifying that the landing
distance is determined in proposed paragraph (a), and replacing
``causing damage or injury'' with ``endangering the airplane and its
occupants.''
    The FAA deletes the phrase ``for landing'' from the introductory
paragraph of Sec.  23.2130. This phrase is unnecessary because the
section is about landing distance. However, the FAA retains the phrase
``the following'' for clarity. For Sec.  23.2130(b), the FAA agrees
that requiring a pilot of average skill ``to meet the landing
distance'' is unclear, but will not replace the term ``meet'' because
changing one word would not make the regulation any clearer. Instead,
the FAA revises the language in Sec.  23.2130(b) to require a pilot of
average skill ``to land within the published landing distance'' and
finds it unnecessary to specify in Sec.  23.2130(b) that the landing
distance is determined in Sec.  23.2130(a). Lastly, the FAA retains the
proposed language ``causing damage or injury'' because the commenter's
recommended change is vague and could cause the regulations to be
interpreted more stringently.
    BendixKing suggested adding language to proposed Sec.  23.130(a)
that would require the speed of 3 knots for water operations to be
relative to the surface in calm atmospheric conditions. Alternatively,
the Associations recommended removing entirely the requirement for
water operations to reach a speed of 3 knots. The commenters agreed
that the term ``stop'' would differ for water and land operations, but
asserted that the difference is not as simple as stating 3 knots. The
commenters stated the appropriate method of compliance for determining
a stop for seaplanes or amphibians should be contained in accepted
standards.
    The FAA agrees with the commenters and removes from the proposed
rule language the requirement for water operations to reach a speed of
3 knots. The speed of 3 knots originated from AC 23-8C, which addresses
water operations. Former Sec.  23.75, the predecessor to Sec.  23.130,
required the airplane to come to a complete stop, and left the surface
type undefined. The FAA intended to clarify rule language by specifying
the speed of 3 knots to differentiate between land and water
operations. However, in light of the comments, the proposed language
added confusion and failed to allow the flexibility necessary for water
operations. The FAA agrees with the commenters that the 3-knot
reference is more appropriate as guidance. Accordingly, Sec.
23.2130(a) now requires the applicant to determine the distance
required to land and come to a stop, starting at a height of 50 feet
above the landing surface. This change removes the need to address
whether the speed of 3 knots must be relative to the surface in calm
atmospheric conditions. The information necessary to comply with Sec.
23.2130(a) will be addressed in means of compliance.
    NJASAP said that wet runway data, as well as contaminated runway
data, should be available for airplane certified to land under the
conditions set forth in proposed Sec.  23.130(a). NJASAP also suggested
the FAA adopt concepts from the Takeoff and Landing Performance
Assessment (TALPA) ARC. NJASAP pointed out that airplanes certified
under part 135 fly in all weather conditions. Finally, NJASAP stated
that runway excursions are a documented risk for these airplanes and
this opportunity offers an additional enhancement.
    While the FAA supports the NJASAP recommendation to make wet runway
data available, doing so should not be a requirement. The TALPA ARC was
primarily a part 25 effort targeting transport operations, not small
airplane operations. The FAA is not adopting the TALPA ARC
recommendations because they exceed former part 23 requirements and are
therefore outside the scope of this rulemaking. The FAA recommends that
NJASAP work with industry to add wet runway conditions to the industry
consensus standards as possible means of compliance for airplanes used
in part 135 operations.
    ANAC recommended the FAA require the landing procedures to allow
for a safe landing, or a transition to a balked landing configuration,
as this would cover the intent of former Sec.  23.75.
    The FAA agrees that proposed Sec.  23.130 (now Sec.  23.2130)
should address the safe transition to the balked landing conditions.
The FAA intended proposed Sec.  23.130 to capture the safety intent of
former Sec. Sec.  23.73 and 23.75. Former Sec.  23.75 required a safe
transition to the balked landing conditions of former Sec.  23.77 from
the conditions that existed at the 50-foot height. The balked landing
conditions are now contained in Sec.  23.2120(c), which captures the
safety intent of former Sec.  23.77. To ensure Sec.  23.2130 contains
the same level of safety as former Sec.  23.75, the FAA revises the
proposed rule language to require an

applicant to determine the approach and landing speeds, configurations,
and procedures that allow for a safe transition to the balked landing
conditions specified in part 23.
    The Associations also recommended the FAA clarify the introductory
sentence of proposed Sec.  23.130 by deleting ``each.'' The FAA agrees
with this comment. Requiring determinations to be made at ``each''
combination of weight and altitude within the operational limits could
be interpreted as requiring an infinite matrix of test points, which
was not the FAA's intent. Rather than requiring the applicant to
determine landing performance at ``each'' combination of weight and
altitude within the operational limits, the FAA is requiring the
determinations to be made at ``critical combinations'' of weight and
altitude. This change is consistent with the change the FAA made to
Sec.  23.2100(b).
h. Controllability (Proposed Sec.  23.200/Now Sec.  23.2135)
    In the NPRM, proposed Sec.  23.200 (now Sec.  23.2135) would have
required--
     The airplane to be controllable and maneuverable, without
requiring exceptional piloting skill, alertness, or strength, within
the operating envelope, at all loading conditions for which
certification is requested. This would have included during low-speed
operations, including stalls, with any probable flight control or
propulsion system failure, and during configuration changes;
     The airplane to be able to complete a landing without
causing damage or serious injury, in the landing configuration at a
speed of VREF minus 5 knots using the approach gradient
equal to the steepest used in the landing distance determination;
     VMC not to exceed VS1 or
VS0 for all practical weights and configurations within the
operating envelope of the airplane for levels 1 and 2 multiengine
airplanes that cannot climb after a critical loss of thrust; and
     An applicant to demonstrate those aerobatic maneuvers for
which certification is requested and determine entry speeds.
    Kestrel questioned whether proposed Sec.  23.200, which is intended
to capture the requirements of former Sec.  23.145, would be
interpreted to include the former requirement to show the airplane can
pitch nose downward when approaching stall, thus avoiding or recovering
from stall, or, alternatively, whether the FAA found that requirement
to be too prescriptive, representing only one possible means of
compliance with the proposed controllability requirements.
    The FAA intended proposed Sec.  23.200 (now Sec.  23.2135) to
capture the safety intent of the former controllability Sec. Sec.
23.141 through 23.157 and allow for other possible means of compliance
appropriate to new or innovative designs. Therefore, proposed Sec.
23.200 was not related only to former Sec.  23.145 and was not intended
to capture the specific requirements of former Sec.  23.145, but did
intend to capture its broader safety intent. The former requirement
referenced by the commenter is prescriptive and provides a means of
compliance for traditional configuration airplanes. Because it is
possible for novel configurations and control schemes in the future to
need different means of compliance, the FAA finds that the prescriptive
language from former Sec.  23.145 is more appropriate as means of
compliance.
    Textron commented on proposed Sec.  23.200(a)(2). Textron pointed
out that former Sec.  23.143(a) and the proposal from the Part 23 ARC
referenced ``all flight phases,'' which better captures the general
intent of former Sec.  23.143(a). Additionally, Textron stated that
proposed Sec.  23.215 addresses stall characteristics, making the stall
aspect of proposed Sec.  23.200(a)(2) redundant. Textron recommended
the FAA maintain language similar to former part 23 by replacing the
phrase ``low-speed operations, including stalls,'' with ``all flight
phases.''
    The FAA agrees with Textron. The FAA's intent in proposed Sec.
23.200(a) (now Sec.  23.2135(a)) was to capture the safety intent of
former Sec.  23.143, which required the airplane to be safely
controllable and maneuverable during all phases of flight. The FAA
agrees that the phrase ``all flight phases'' better captures the safety
intent of former Sec.  23.143(a). Additionally, upon further review,
the language of proposed Sec.  23.200(a)(2) is confusing because, while
the FAA proposed to add requirements to essentially avoid the stall
maneuver in proposed Sec.  23.215, proposed Sec.  23.200(a)(2) would
have required controllability in the stall. While this is a desirable
and recommended condition, the FAA does not want to add confusion. The
stall requirements belong in proposed Sec.  23.215 (now Sec.  23.2150).
For these reasons, the FAA adopts Textron's recommendation.
    Textron also commented on proposed Sec.  23.200(a)(3). Textron
noted that former Sec.  23.143 and the proposal from the Part 23 ARC
did not address failures other than a response to a sudden engine
failure. Textron also noted that proposed Sec.  23.1315 already covers
general airplane system or equipment failures. Textron claimed the
requirements of proposed Sec.  23.200(a)(3) could be interpreted as
requiring demonstration of all probable flight control and propulsion
failures in a flight-test environment, which the commenter said would
not be practical or safe. Textron recommended maintaining the
traditional scope of former subpart B controllability requirements,
which included normal operations and, for multiengine airplanes, the
response to critical loss of thrust, and using the methods employed for
proposed Sec.  23.1315 to evaluate responses to other failures.
    In light of Textron's comment, the FAA finds it necessary to
clarify that Sec.  23.2135(a)(3) applies to ``reversible,'' which were
traditionally mechanical flight controls, not ``irreversible'' flight
controls. The FAA's intent in proposed Sec.  23.200(a) was to capture
the safety intent of former Sec. Sec.  23.145(e) and 23.147(c), which
required applicants to address mechanical control system failures.
Historically, these requirements targeted control cable failures or
push-pull tube disconnects. Former subpart F, which contained
requirements on equipment, addressed powered- and computer-controlled
flight control systems. Under this final rule, subpart F continues to
address equipment, such as powered- and computer-controlled flight
control systems, and Sec.  23.2135 addresses mechanical control system
failures, which is consistent with former Sec. Sec.  23.145(e) and
23.147(c).
    The Associations and EASA also addressed proposed Sec.
23.200(a)(3).\25\ The Associations recommended the FAA delete the word
``any'' from the phrase ``any probable flight control or propulsion
system failure.'' EASA recommended the FAA replace the word
``probable'' with ``likely,'' to avoid creating ambiguity with
probability definitions.
---------------------------------------------------------------------------

    \25\ EASA actually referred to proposed Sec.  23.200(a)(4) in
its comment, but the FAA assumes EASA meant to refer to proposed
Sec.  23.200(a)(3), which is where the term ``probable'' is used.
---------------------------------------------------------------------------

    The FAA agrees the term ``any'' does not add value compared to the
potential for confusion coming from an absolute qualifier. The FAA
therefore deletes the word ``any'' in Sec.  23.2135(a)(3).
    The FAA also agrees the term ``probable'' has specific meaning
relative to systems. Furthermore, the FAA expects a transition from
mechanical flight controls to computer-controlled flight control
systems, which are covered under the requirements in subpart F. Because
the term ``probable''

has the potential to create confusion between the flight test
requirements of subpart B and the systems requirements of subpart F,
the FAA is using the term ``likely,'' rather than ``probable,'' which
will reduce the potential for confusion while maintaining the intent of
the requirement. For more detailed discussion on the use of ``likely'',
please refer to the discussion on proposed Sec.  23.205 (now Sec.
23.2140).
    The Associations commented on proposed Sec.  23.200(b), stating
that it does not account for preferred technologies, such as angle of
attack indicators, for executing safe approach and landing procedures.
The commenters recommended proposed paragraph (b) require the airplane
to complete a safe landing when following the landing procedures;
providing a safe margin below Vref or above angle of attack.
EASA recommended removing the configuration details and specific speed
margin from proposed Sec.  23.200(b) because future designs would not
be able to comply with them.
    The FAA agrees with these comments. The FAA intended proposed Sec.
23.200(b) (now Sec.  23.2135(b)) to capture the safety intent of former
Sec.  23.153 for control during landings. The FAA agrees that
specifying a prescriptive speed of Vref minus 5 knots, which
former Sec.  23.153 required, may not be appropriate for entry-level
airplanes with very-low landing speeds and may not even apply to new
configurations. The FAA therefore removes this prescriptive speed.
Instead, the FAA is requiring a reasonable margin below Vref
or above approach angle of attack, as recommended by the Associations.
This change from what was proposed is consistent with the safety intent
of former Sec.  23.153 as it requires a safe speed margin and it
accounts for entry-level airplanes and new technology. The FAA also
deletes the phrase ``equal to the steepest used in the landing distance
determination'' and replaces it with ``steepest approved'' approach
gradient procedures as this is clarifying.
    Textron recommended proposed Sec.  23.200(b) be modified to require
the airplane to land without ``endangering the airplane and its
occupants,'' rather than to land without ``causing damage or serious
injury.''
    The FAA finds that Textron's recommendation does not capture the
safety intent of former Sec.  23.153, which required safe completion of
a landing. However, in light of Textron's comment, the FAA is
clarifying the term ``damage.'' As proposed in the NPRM, the rule would
not have allowed any damage, no matter how trivial. This was not the
intent of former Sec.  23.153. The FAA intended to capture the safety
intent of former Sec.  23.153 in proposed Sec.  23.200(b) (now Sec.
23.2135(b)); therefore, the FAA revises the proposed rule language by
defining the damage that could be accepted during demonstration.
Section 23.2135(b) now requires the airplane to be able to complete a
landing without causing ``substantial'' damage or serious injury.
Substantial damage is defined in 49 CFR part 830 as requiring major
repairs and effectively preclude the use of the airplane for its
intended purpose.
    Textron also noted that proposed Sec.  23.200 would not have
required VMC to be determined. ANAC and Textron recommended
the FAA require VMC to be determined, because it must be
accounted for in the determination of takeoff performance. Textron
recommended adding a new paragraph to proposed Sec.  23.200. Textron
recommended the new paragraph state VMC is the calibrated
airspeed at which, following the sudden critical loss of thrust, it is
possible to maintain control of the airplane. For multiengine
airplanes, the applicant must determine VMC for each flight
configuration used in takeoff and landing operations.
    The FAA agrees the rule should require VMC to be
determined. Proposed Sec.  23.200 was intended to capture the safety
intent of former Sec.  23.149, which defined and required the
determination of VMC. The FAA is adding language to Sec.
23.2135(c) that is consistent with former Sec.  23.149, but removes the
prescriptive requirements of former Sec.  23.149, such as the specific
configuration requirements. Section 23.2135(c) now states that
VMC is the calibrated airspeed at which, following the
sudden critical loss of thrust, it is possible to maintain control of
the airplane. Section 23.2135(c) also requires the applicant to
determine VMC, if applicable, for the most critical
configurations used in the takeoff and landing operations. The FAA is
requiring the applicant to determine VMC in the most
``critical'' configurations rather than in ``each'' configuration
because requiring the determination at each configuration would present
an infinite number of test points. Additionally, the FAA added the
phrase ``if applicable'' to the rule language because there are
multiengine airplanes that do not have a VMC.
    ANAC recommended proposed Sec.  23.200(c) be written in a less
prescriptive manner to allow for different technology solutions. ANAC
stated that proposed Sec.  23.200(c) should contain only the safety
objective stated in the NPRM. For example, proposed Sec.  23.200 should
have stated that an airplane should not depart controlled flight at low
speeds above stall as a result of asymmetric thrust.
    The Associations stated that while proposed Sec.  23.200(c)
represented a potential solution to the typical accident scenario
involving loss of control in multiengine airplanes, which are unable to
climb on a single engine, there are other solutions that may be better
depending on the design of the airplane. The commenters noted that
instead of assuring VMC is below the stall speed, solutions
might include envelope protection, increased awareness of the loss of
control condition, or automatic-power response. To ensure the rule
allows the best solution for a particular design, the commenters
recommended the FAA not adopt proposed Sec.  23.200(c). Instead, the
commenters recommended the section on loss of control, proposed Sec.
23.215, require multi-engine airplanes, not certified for aerobatics,
not have a tendency to suffer a loss of control after a likely critical
loss of thrust. Several other commenters also expressed concerns about
proposed Sec.  23.200(c) and made similar recommendations.
    As explained in the NPRM, the critical safety issue that the FAA
intended proposed Sec.  23.200(c) to address was the loss of control
caused by asymmetric thrust. The FAA recognized in the NPRM concerns
regarding the effectiveness of the proposed requirement in addressing
loss of control caused by asymmetric thrust and requested comments on
the proposal. In light of the comments received, the FAA is not
adopting proposed Sec.  23.200(c). The FAA agrees with ANAC and the
Associations that the rule should allow for different technologies as
design solutions to the identified safety issue. The FAA also agrees
that Sec.  23.2150 should include the requirement to address this loss
of control issue. Therefore, the FAA adopts less prescriptive language
similar to that recommended by the commenters, which is consistent with
the intent of proposed Sec.  23.200(c). This will allow for alternative
design solutions. Section 23.2150(c) now requires levels 1 and 2
multiengine airplanes, not certified for aerobatics, to not have a
tendency to inadvertently depart controlled flight from thrust
asymmetry after a critical loss of thrust.
    The Associations and EASA recommended the FAA apply this
requirement to all multiengine airplanes, rather than only levels 1 and
2. The FAA is not adopting this recommendation. As explained in the
NPRM, the FAA does not have the accident history data to support it.
The FAA encourages manufacturers of levels

3 and 4 multiengine airplanes to incorporate safety features that
prevent inadvertent departure as with levels 1 and 2 multiengine
airplanes.
    ICON commented an airplane designed in accordance with proposed
Sec.  23.200(c) would require less skill and presence of mind during an
emergency, resulting in better safety.
    While the FAA is not adopting proposed Sec.  23.200(c), new Sec.
23.2150(c) achieves the safety objective of proposed Sec.  23.200(c).
    Transport Canada noted the reason for requiring VMC to
be less than the stall speed is to avoid loss of control following an
engine failure. Transport Canada suggested an airplane designed with a
large enough rudder to meet this requirement may be more prone to
inadvertent spin entries. Transport Canada recommended requiring all
multiengine airplane to have a positive climb gradient following an
engine failure.
    As explained in the NPRM, while the Part 23 ARC discussed the
option that all multiengine airplanes have guaranteed climb performance
after a critical loss of thrust, the FAA ultimately rejected this
option because it could impose a significant cost on the production of
training airplanes.
i. Trim (Proposed Sec.  23.205/Now Sec.  23.2140)
    In the NPRM, proposed Sec.  23.205 (now Sec.  23.2140) would have
required the airplane to maintain longitudinal, lateral, and
directional trim under various conditions, depending on the airplane's
certification level, without allowing residual forces to fatigue or
distract the pilot during likely emergency operations, including a
critical loss of thrust on multiengine airplanes.
    EASA commented the text of proposed Sec.  23.205 failed to take
into account residual forces for lateral and directional control for
those level 1, 2, and 3 airplanes with ground-adjustable trim tabs.
    The FAA agrees with EASA that while the FAA addressed ground-
adjustable trim tabs for level 1, 2, and 3 airplanes, the proposed rule
failed to account for residual forces in lateral and directional axes.
The FAA intended for proposed Sec.  23.205 to maintain the level of
safety found in former Sec.  23.161. Former Sec.  23.161(a), which
applied generally to all airplanes and to lateral, directional, and
longitudinal trim, stated that it must be possible to ensure the pilot
will not be unduly fatigued or distracted by the need to apply residual
control forces exceeding those for prolonged application of former
Sec.  23.143(c) in normal operations of the airplane. In light of
EASA's comment, the FAA recognizes that proposed Sec.  23.205 (now
Sec.  23.2140) would only have prohibited residual control forces from
fatiguing or distracting the pilot during likely emergency conditions.
The FAA agrees with EASA that the rule should account for residual
control forces in lateral and directional axes for levels 1, 2, and 3
airplanes. However, to maintain the same level of safety as former
Sec.  23.161, the rule should also account for residual control forces
in longitudinal axes and should apply generally to levels 1, 2, 3, and
4 airplanes. Accordingly, the FAA is adding the requirement for
residual control forces not to fatigue or distract the pilot during
normal operations of the airplane to Sec.  23.2140(c). This requirement
is consistent with former Sec.  23.161(a).
    Textron noted that the reference ``normal operations'' would
require all level 4 airplanes to be able to trim in all three axes from
obstacle height to obstacle height. Textron contended that would seem
to increase the burden from the former requirements in Sec.  23.161, at
least regarding lateral and directional trim.
    The FAA considered Textron's comment, but is retaining the
reference to ``normal operations'' in proposed Sec.  23.205(a)(2) (now
Sec.  23.2140(a)(2)). While Sec.  23.2140(a)(2) could be interpreted
more stringently than former Sec.  23.161(b)(2), the FAA never intended
the proposed language to increase the burden from the previous
requirements. Former Sec.  23.161 required lateral and directional trim
for commuter category airplanes, which are the equivalent of level 4
airplanes, at all speeds from 1.4VS1 to the lesser of
VH or VMO/MMO. The objective of the
proposed rule was to allow the prescriptive requirements of former
Sec.  23.161 to be addressed in means of compliance. While specific
speeds such as 1.4VS1 are appropriate as the lower speed
limit for defining ``normal operations'' for traditional configurations
of level 4 airplanes, it may not fit new airplanes with novel
propulsion, high lift, and flight control system configurations. For
this reason, the FAA finds the proposed language of ``normal
operations'' best addresses the top-level safety requirement of former
Sec.  23.161(b)(2) while allowing the appropriate speed range to be
addressed in means of compliance.
    In reference not only to this section, but also to its use
throughout the proposed rule, ANAC commented that the term ``likely''
is not precise and should be clarified or replaced with more precise
terms such as ``probable'', ``remote'', or ``not extremely
improbable.''
    The FAA infers that ANAC recommended using a quantitative term,
such as ``probable,'' because it is defined in guidance material. While
the FAA agrees with ANAC's comment that the term ``likely'' is not
precise, the FAA intends to allow some imprecision for the objective of
providing performance-based standards that are sufficiently flexible to
accommodate new technologies. The term ``likely'' was chosen to mean a
reasonable expectation based on the existing conditions. This is
consistent with the former usage of the term throughout part 23.
Clarification of what should or should not be considered likely for a
particular rule will be provided in the means of compliance.
    Textron recommended deleting the qualifying term ``likely'' from
proposed Sec.  23.205(c) because it would be subject to interpretation.
Textron also recommended adding abnormal operations to those operations
during which residual control forces must not fatigue or distract the
pilot. Lastly, Textron recommended a few editorial changes, including
adding the term ``control'' to residual forces.
    While Textron took exception to the word ``likely'' to describe
emergency operations, the FAA finds the term to be appropriate in this
case. Deleting the qualifier ``likely'' could actually lead to more
stringent interpretations of the requirement. The term ``likely''
bounds the requirement within rational and probable emergencies. Simply
using the term ``emergency'' could be construed as requiring an
applicant to address any possible emergency regardless of how
improbable it is.
    The FAA agrees with Textron concerning the addition of abnormal
operations. Former Sec.  23.161 referenced the specific condition of an
engine failure, which would have been based on traditional engine
configuration on the wing. Looking ahead, that failure condition could
be considered an abnormal and/or an emergency operation depending on
the number of engines, location, and control of the engines.
Furthermore, there may be other types of failures where trim would be
important. For these reasons, the FAA finds that addressing the
situation using the performance-based terms of ``abnormal'' and
``emergency'' is appropriate and consistent with the objective of
providing performance-based standards that are sufficiently flexible to
accommodate new technologies.
    The FAA also agrees with Textron's recommendation to add
``control'' to

residual forces. The FAA notes that former Sec.  23.161 referenced
``residual control forces,'' not ``residual forces.'' This was an
oversight in the NPRM. Accordingly, Sec.  23.2140(c) now prohibits
residual control forces from fatiguing or distracting the pilot during
likely abnormal or emergency operations.
    The Associations and Textron recommended streamlining the proposed
rule language by moving a phrase that appeared twice in proposed Sec.
23.205(a)(1) and (2) to a single, earlier reference in proposed Sec.
23.205(a).
    The FAA agrees with the commenters and has adopted their
recommendation. Section 23.2140(a) now requires the airplane to
maintain lateral and directional trim without further force upon, or
movement of, the primary flight controls or corresponding trim controls
by the pilot, or the flight control system, under the conditions
specified in paragraphs (a)(1) and (a)(2). This marks a change from
what was proposed in the NPRM in that paragraph (a) no longer addresses
longitudinal trim. The FAA removed the reference to longitudinal trim
in paragraph (a) because longitudinal trim is addressed by paragraph
(b).
    Furthermore, the FAA is adding language to paragraph (b) that
requires the longitudinal trim to be maintained without further force
upon, or movement of, the primary flight controls or corresponding trim
controls by the pilot, or the flight control system, under the
conditions specified in paragraphs (b)(1) through (b)(4). This
requirement, which is consistent with the intent of the NPRM, ensures
Sec.  23.2140(b) maintains the same level of safety as former Sec.
23.161. Former Sec.  23.161(a) required each airplane to meet the trim
requirements of former Sec.  23.161 after being trimmed and without
further pressure upon, or movement of, the primary flight controls or
their corresponding trim controls by the pilot or the automatic pilot.
This requirement applied generally to lateral, directional, and
longitudinal trim.
j. Stability (Proposed Sec.  23.210/Now Sec.  23.2145)
    In the NPRM, proposed Sec.  23.210 (now Sec.  23.2145) would have
required airplanes not certified for aerobatics to have the following
in normal operations: (1) Static longitudinal, lateral, and directional
stability, and (2) dynamic short period and combined lateral
directional stability. Proposed Sec.  23.210 would have also required
airplanes not certified for aerobatics to provide stable control force
feedback throughout the operating envelope. Additionally, proposed
Sec.  23.210 would have precluded any airplane from exhibiting any
divergent stability characteristic so unstable as to increase the
pilot's workload or otherwise endanger the airplane and its occupants.
    Kestrel suggested removing the phrase ``in normal operations'' from
proposed Sec.  23.210(a)(1) because it could be interpreted to mean
that static stability is not required in abnormal operations.
    The FAA understands Kestrel's concern with the phrase ``in normal
operations'' in the proposed language. However, the FAA intended
proposed Sec.  23.210(a) (now Sec.  23.2145(a)) to capture the safety
intent of the stability sections in former part 23, which did not
require demonstrations in abnormal or emergency conditions. Former
Sec.  23.171 required an airplane to show static stability in ``any
condition normally encountered in service,'' which the FAA considers to
be normal operations. The former requirements have provided an
acceptable level of safety. The FAA adopts the proposed language in
Sec.  23.2145(a)(1) as proposed.
    Optimal stated that proposed Sec.  23.210(a)(2) appears to require
that all lateral modes be stable, implying that airplane need to be
spirally stable. This commenter indicated that most airplane have
divergent spiral modes and therefore could not meet this requirement as
proposed.
    The FAA agrees with Optimal that the proposed requirement could be
interpreted as including spiral mode. The FAA intended proposed Sec.
23.210(a)(2) to capture the short period and Dutch-roll stability that
former part 23 required. ``Combined lateral-directional oscillations''
means ``Dutch roll.'' The FAA revises the language in Sec.
23.2145(a)(2) to replace ``combined lateral-directional stability''
with ``Dutch roll'' stability.
    ANAC suggested including the terms ``adequate'' or ``appropriate''
to qualify dynamic stability in proposed Sec.  23.210(a)(2).\26\ ANAC
stated that requiring only a showing of stability may allow for the
interpretation that ``marginally stable'' is acceptable, while current
part 23 has minimum damping factors prescribed.
---------------------------------------------------------------------------

    \26\ ANAC actually addressed this comment to Sec.  23.205(a)(2),
but it appears it was supposed to address Sec.  23.210(a)(2).
---------------------------------------------------------------------------

    The FAA agrees with ANAC that requiring only stability without a
qualifier could allow for interpretations outside of the prescriptive
standards of former part 23. However, the FAA does not agree with
qualifying stability in Sec.  23.2145(a)(2). Under the new part 23,
applicants will have to propose a means of compliance. While this is a
significant change from the former part 23, the language in Sec.
23.2145(a)(2) will enable the FAA to accept the current prescriptive
limits as a means of compliance. Alternatively, if a new technology
requires something different, the FAA can accept what is appropriate.
    NJASAP suggested the ``Dutch roll'' characteristic on the EMB505
airplane is close to the language used in proposed Sec.  23.210(b).
NJASAP sought to ensure any stability system used to comply with this
section is not so dependent on Global Positioning System (GPS)
technology that its loss or interruption could cause the electronic
augmentation system to fail.
    NJASAP's comment is outside the scope of this section as the FAA
proposed Sec.  23.210 (now Sec.  23.2145) to include requirements for
flight controls, not for their underlying systems. The FAA notes,
however, that flight control systems used to comply with this section
must also meet the system requirements of subpart F, which adequately
address the commenter's concern.
k. Stall Characteristics, Stall Warning, and Spins (Proposed Sec.
23.215/Now Sec.  23.2150)
    In the NPRM, proposed Sec.  23.215 (now Sec.  23.2150) would have
required an airplane to have controllable stall characteristics in
straight flight, turning flight, and accelerated turning flight with a
clear and distinctive stall warning that provides sufficient margin to
prevent inadvertent stalling. Proposed Sec.  23.215 would have allowed
for alternative approaches to meeting this requirement for levels 1 and
2 airplanes and level 3 single-engine airplanes, not certified for
aerobatics, in order to avoid a tendency to inadvertently depart
controlled flight. Proposed Sec.  23.215 would have also required
airplanes certified for aerobatics to have controllable stall
characteristics and the ability to recover within one and one-half
additional turns after initiation of the first control action from any
point in a spin, not exceeding six turns or any greater number of turns
for which certification is requested while remaining within the
operating limitations of the airplane. Proposed Sec.  23.215 would have
also 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.
    Garmin commented that while the proposal contained a lengthy
discussion about requirements to improve the

airplane's resistance to departing controlled flight, proposed Sec.
23.215(a) would only have required the airplane to have controllable
stall characteristics in straight, turning and accelerated flight.
Garmin stated there was no mention of flight characteristics related to
control usage at the stall that does not precisely and correctly
control the stall. As an example, Garmin noted an applicant can comply
with the rule and have an airplane that is controllable through a stall
if flown correctly, but if not flown correctly, can enter an
uncontrollable spin if the airplane is allowed to stall while not
precisely coordinated. Garmin recommended the FAA change either the
rule or the preamble to be consistent with each other.
    The FAA acknowledges the NPRM preamble discussion may have been
unclear. The FAA only intended proposed Sec.  23.215(b) (now Sec.
23.2150(b) to improve an airplane's resistance to departing controlled
flight. This increase in level of safety applied only to the smaller
part 23 airplanes, not all part 23 airplanes. Furthermore, the FAA
intended for proposed Sec.  23.215(a) to capture the safety intent of
former Sec. Sec.  23.201 and 23.203. Garmin's example will continue to
be true for airplanes not required to meet Sec.  23.2150(b). The FAA
notes that Sec.  23.2150(a) will not include requirements related to
conditions and control usage at the stall. While former Sec. Sec.
23.201 and 23.203 included these requirements, the FAA finds they are
better addressed in means of compliance.
    The FAA notes the details from these former rules will be addressed
in the means of compliance and will remain essentially unchanged,
especially for larger, higher-performance airplanes. The reason is that
the accident history of the larger airplanes does not warrant the
change. The means of compliance for the level 1 and 2 airplanes and
level 3 single-engine airplanes is expected to allow for more
alternative approaches from what is acceptable today to meet the higher
level of safety in this rule.
    Textron and the Associations commented that Sec.  23.215(b) should
not require multiengine airplanes to not have a tendency to
inadvertently depart controlled flight. The commenters explained that
loss of control accidents involving multiengine airplanes result mostly
from pilots failing to maintain directional control following a
critical loss of thrust. Textron noted that this concern is being
addressed by proposed Sec.  23.200(c), which proposes new requirements
for airplanes that cannot climb after a critical loss of thrust.
Textron also noted former Sec.  23.221 was not a requirement for
multiengine airplanes and that proposed Sec.  23.215(b) would have
represented a significant new burden with no safety justification.
    The Associations stated it believed loss of control accidents
predominately involve single-engine airplanes, or multiengine airplanes
during a critical loss of thrust event. The Associations recommended
that the FAA revise proposed Sec.  23.215 to ensure the loss of control
requirements are applied in a manner that will maximize safety while
being applied in an efficient manner. The Associations specifically
recommended the FAA revise proposed Sec.  23.215 to require multiengine
airplanes, not certified for aerobatics, to not have a tendency to
suffer a loss of control after a likely critical loss of thrust. This
would be an alternative to adopting proposed Sec.  23.200(c). The
Associations also recommended the FAA revise the proposed Sec.
23.215(b) to require single-engine airplanes, not certified for
aerobatics, to not have a tendency to inadvertently depart controlled
flight.
    The FAA agrees that proposed Sec.  23.215(b) (now Sec.  23.2150(b))
should apply only to single-engine airplanes. The FAA proposed to apply
paragraph (b) to level 1 and 2 multiengine airplanes in an attempt to
address the loss of control accidents in light multiengine airplanes
that can occur after an engine failure if the pilot does not maintain a
safe single-engine speed. However, as noted by Textron, the FAA
proposed Sec.  23.200(c) to address this safety issue by requiring that
Vmc not exceed Vs1 or Vso. In light of
the comments, the FAA recognizes it is more appropriate to address the
loss of control issue for light multiengine airplanes in Sec.  23.2150
rather than Sec.  23.2135 because it is redundant to address the issue
in both sections. The FAA revises Sec.  23.2150(b) in this final rule
to reflect that it only applies to single-engine airplanes in all
certification levels to be consistent with former Sec.  23.221. While
the FAA did not propose in the NPRM that level 4 single-engine
airplanes would be subject to this requirement, extending this
requirement to such airplanes is a logical outgrowth from the proposal
because the same safety benefit applies regardless of certification
level. Also, the FAA finds no valid technical basis for excluding level
4 airplanes from this requirement. The airplane categories in former
part 23 did not provide for certification of single-engine airplanes
with passenger capacities greater than nine; however, it is possible
that applicants may seek approval for such an airplane in the future.
In such cases, these airplanes will have the same level of safety as
smaller single-engine airplanes.
    As discussed in the preamble discussion of Sec.  23.2135, the FAA
is withdrawing proposed Sec.  23.200(c) and adding a new Sec.
23.2150(c). Paragraph (c) requires levels 1 and 2 multiengine
airplanes, not certified for aerobatics, to not have a tendency to
inadvertently depart controlled flight from thrust asymmetry after a
critical loss of thrust. The FAA finds that paragraphs (b) and (c), as
revised, more accurately reflect the FAA's intent regarding the
prevention of loss of control accidents in both single and multi-engine
airplanes.
    EASA commented that proposed Sec.  23.215(b) would not have
provided the flexibility needed for future designs. EASA recommended
the FAA allow levels 1 and 2 airplanes and level 3 single-engine
airplanes not certified for aerobatics to meet one of three
alternatives: (1) Not to have the tendency to inadvertently depart
controlled flight; (2) have a benign behavior when departing controlled
flight; or (3) have a system preventing departure from controlled
flight.
    While the FAA understands EASA's recommended approach, Sec.
23.2150(b) and (c) contain the most significant safety improvements in
this rulemaking effort. Any departure from controlled flight is likely
to result in a fatal accident unless an experienced pilot demonstrating
spins in an aerobatic airplane intentionally does it. Allowing levels 1
or 2 airplanes or level 3 single-engine airplanes to have a benign
behavior when departing controlled flight would not meet the FAA's
safety objective for airplanes that are not certified for aerobatics.
The FAA notes that an airplane that can depart controlled flight with
benign behavior can inadvertently depart controlled flight.
Furthermore, having a system that prevents departure from controlled
flight may be a means of compliance for Sec.  23.2150(b). Therefore,
the FAA finds it inappropriate to offer it as an alternative in the
regulation.
    The FAA did not intend Sec.  23.2150(b) to be absolute in that
``spin resistance'' is the only way to meet the rule. An airplane using
enhanced stall warnings and envelope protection could be very difficult
to depart from controlled flight and comply with Sec.  23.2150(b). That
same airplane, with some effort, could be made to spin (depart
controlled flight) and have good recovery capability and still--because
of the stall characteristics and the enhanced warning and systems
protection--comply with the new requirement. The

FAA is working on means of compliance that will allow numerous
combinations of airframe and systems approaches to complying with the
new requirement so that applicants have alternative ways to comply with
the regulation. Furthermore, this approach will encourage the
development of new innovative technology that targets resistance to
departure from controlled flight.
    Several commenters took issue with the proposed requirement in
Sec.  23.215(b) that certain airplanes must not have a tendency to
inadvertently depart controlled flight. Air Tractor, Optimal, and an
individual commenter noted the proposal does not define this phrase.
The individual commenter asked whether this phrase includes proper use
of flight controls, improper use of flight controls, conditions beyond
and per former Sec.  23.221(a)(2) for spin resistance. Air Tractor
stated it would be difficult to prove an airplane meets this
requirement.
    The FAA purposely used language that would allow flexibility in
showing compliance. The FAA recognizes the lack of clear, detailed
requirements may increase the difficulty of proving that the airplane
meets this requirement. However, the FAA finds providing clear,
detailed requirements would prevent the acceptance of alternative
approaches to this safety problem. It could also prevent the use of new
technology, which would discourage the development of even newer
technology. As explained in the NPRM, the FAA envisions numerous
alternative approaches to meeting this requirement, ranging from a
stick pusher to full spin resistance. The FAA is relying on industry to
develop acceptable means of compliance beyond these two acceptable
approaches for this requirement, should industry fully leverage the
flexibility the FAA built into the rule. The FAA is also relying on
industry to incorporate new technologies into the airplane to address
stall-based accidents. Currently, the ASTM committee is maturing an
innovative approach that incorporates many of the variables associated
with stall characteristics to prevent inadvertent departures from
controlled flights.
    Air Tractor expressed concern that it may not be able to comply
with the intent of the proposed requirement because its airplanes are
designed to operate close to the ground and sometimes close to a stall.
According to Air Tractor, if it were to add some kind of substantial
departure resistance to prevent inadvertent stalls resulting in a
departure from controlled flight, as described in the NPRM, this
modification could potentially increase pilot fatigue significantly.
    The FAA notes that Air Tractor's airplanes are certified in
restricted category and have the latitude to modify the part 23
requirements where necessary. For example, as Air Tractor pointed out,
its airplanes are designed to operate close to the ground and sometimes
close to a stall. For this reason, Air Tractor did not have to meet the
one-turn spin requirement from former part 23 as specified on TCDS
Number A19SW. However, because Air Tractor's airplanes are operated
close to the ground and sometimes close to a stall, characteristics or
features that prevent inadvertent departure would be desirable, unless
these characteristics or features add control forces that fatigue the
pilot or reduce maneuverability. The FAA finds these issues apply only
to a small subset of airplanes and can be addressed most efficiently
and effectively in the certification context, rather than by revising
the regulatory text. Optimal expressed concern with unintended
consequences that may result from imposing departure from controlled
flight resistance requirements. Specifically, it questioned whether
proposed Sec.  23.215(b) can be satisfied without compromising other
aspects of the airplane's performance and handling.
    The FAA notes that, historically, when only using traditional
mechanical controls, there are performance and handling tradeoffs that
can come from imposing departure resistance requirements. This is one
reason the FAA has been reluctant to push for departure resistant
characteristics in the past. However, the development, availability,
and cost of new technology to address departure resistance have matured
such that the FAA believes it is time to introduce this requirement to
reduce loss of control accidents. Aerodynamics and systems combined can
address departure resistance without compromising performance and
handling. The FAA will not accept a means of compliance that has a
detrimental effect on safety.
    Transport Canada questioned whether proposed Sec.  23.215(b) would
result in designs that have a significant effect on the loss of control
accident rate and asked what the flight test requirements would be for
demonstrating compliance with paragraph (b). American Champion Aircraft
Corporation (American Champion) stated the regulation should provide a
means to determine acceptable departure resistance, or a description of
an acceptable means of compliance.
    The FAA recognizes that the means of compliance will be very
important in the success of this requirement to improve safety. The FAA
adopts a general performance-based requirement in Sec.  23.2150(b) to
enable numerous alternative approaches to meet the requirement. For
this reason, it is impossible to specify a single set of flight test
requirements. The flight test requirements will depend on the
applicant's approach to complying with this rule and the means of
compliance it uses. It would have been impossible to adopt requirements
for all combinations of safety features and characteristics that reduce
the tendency to inadvertently depart controlled flight in the
requirements themselves. However, applicants can still use the spin
resistance requirements from former Sec.  23.221 for spins, and a stick
pusher compliant with former Sec.  23.691 for artificial stall barrier
systems. Additionally, ASTM is developing an expandable matrix concept
that will allow credit for combinations of stall warning, stall/
envelope protection, and flight characteristics. This matrix should
result in not only encouraging manufacturers to install more safety
enhancing equipment, but more importantly, it will also encourage the
development of innovative approaches to preventing inadvertent
departure because of the speed at which new technology can be
incorporated into the certification process. To address the wide range
of airplane characteristics and solutions, the FAA is adopting a
standard that the airplane may not have tendency to inadvertently
depart controlled flight.
    American Champion noted inconsistencies with the required degree of
departure resistance throughout the NPRM. For example, the commenter
noted proposed Sec.  23.215(b) stated ``must not have a tendency to
inadvertently depart controlled flight.'' Section V of the NPRM
referred to departure resistant as ``stall characteristics that make it
very difficult for the airplane to depart controlled flight,'' and
section VI states certification levels would have required
``substantial departure resistance.'' American Champion recommended the
FAA clarify the degree of departure resistance intended by proposed
Sec.  23.215(b).
    The FAA notes Sec.  23.2150(b) states that single-engine airplanes,
not certified for aerobatics, ``must not have a tendency'' to
inadvertently depart controlled flight. Therefore, ``must not have a
tendency'' is the standard. The FAA acknowledges, however, that the
NPRM discussions should have been more consistent when discussing the
proposed rule language.

    Optimal expressed concern about removing the requirement for
single-engine airplanes not certified for aerobatics to recover from a
one-turn/three-second spin at this time because pilots have been adept
at finding unanticipated ways to get spin resistant airplanes to depart
from controlled flight and because airplanes that are the most
reluctant to spin tend to be the most reluctant to recover. Optimal
recommended the FAA retain the requirement to recover from an incipient
spin until sufficient certification and operational experience has been
acquired with departure resistant airplanes.
    The FAA removes the requirement for the one-turn/three-second spin
for normal category single-engine airplanes. Historically, airplanes
that were reluctant to spin tended to be reluctant to recover. This
history is based on airplanes with inherent stability and reversible
controls, which to date are all small airplanes. The FAA intentionally
focused on the prevention of the conditions that lead to an inadvertent
spin (departing controlled flight) versus the historical focus on spin
recovery. For decades, the FAA has focused on spin recovery in
certification programs only to have those same certified airplanes
depart controlled flight at altitudes so low that even experienced
pilots could not recover. For decades, this scenario has accounted for
a large percentage of fatal accidents. The FAA has to change the
approach to certification in order to reduce the number of departure
from controlled flight fatal accidents.
    Kestrel expressed concern that demonstrating compliance to proposed
Sec.  23.215(d) would be prohibitively expensive and potentially
impossible. Kestrel suggested the FAA modify the proposed rule language
to read ``with any typical use of the flight or engine power
controls.''
    The FAA agrees that proposed Sec.  23.215(d)(1) (now Sec.
23.2150(e)(1)) could have been interpreted as imposing an unbounded
requirement, which was not the FAA's intent. The FAA revises the
proposed rule language as Kestrel suggested.
    EASA commented that proposed Sec.  23.215(d)(2) (now Sec.
23.2150(e)(2)) would have contained a flightcrew interface requirement
that does not belong in the airworthiness (design) requirements. EASA
recommended the FAA move this requirement to subpart G, which addresses
flightcrew interface requirements.
    The FAA is retaining the requirement in subpart B because it
originated from former subpart B, Sec.  23.221(c). The FAA finds that
keeping it in the same subpart, in this instance, will avoid confusion.
    American Champion commented that it is unnecessary to restrict
certification of dual-purpose airplanes by requiring a mechanical or
electronic change, as described in the NPRM, because airplanes can both
meet the enhanced stall characteristics and also be suitable for some
aerobatic maneuvers. The commenter noted that departure resistance,
proposed Sec.  23.215(b), does not preclude an airplane from aerobatic
maneuvering, although it may affect the ability of the airplane to
enter a spin.
    The FAA proposed to restrict certification of new airplanes for
dual use to prevent inadvertent stalls, which was one of the proposal's
objectives. If an airplane can spin for spin training, then the
airplane can inadvertently stall and depart into a spin during normal
operations. In light of American Champion's comment, however, the FAA
acknowledges there may be airplanes in the future that are approved for
limited aerobatics that do not include spins. This would be similar to
military fighter airplane. The military approach has historically been
to explore thoroughly the post stall regime including spins and