airplanes and, for this reason, the FAA proposes to make all airplanes
certificated under part 23 use 50 feet (15 meters) above the takeoff
surface.
vi. Proposed Sec.  23.125, Climb Information
    Proposed Sec.  23.125 would require an applicant to determine the
climb performance for--
     All single engine airplanes;
     Certification 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 also require an applicant to determine
the glide performance of the airplane after a complete loss of thrust
for single engine airplanes.
    Proposed Sec.  23.125 would capture the safety intent of current
Sec. Sec.  23.63, Climb: General; 23.66, Takeoff climb: One-engine
inoperative; 23.69, Enroute climb/descent; and 23.71, Glide: Single-
engine airplanes. The intent of these requirements is to provide pilots
with climb and glide performance data that is important for safety,
especially in conditions near the performance limits of the airplane.
Sections 23.63, 23.66, and 23.69 are not minimum performance sections,
but contain information used in the development of the AFM. Proposed
Sec.  23.125 would require an applicant to determine climb performance.
The performance data determination provides a good example of how the
use of certification levels can allow simplified approaches to meet
applicable airworthiness requirements for simple, and levels 1 and 2
airplanes.
vii. Proposed Sec.  23.130, Landing
    Proposed Sec.  23.130 would require 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 require these
determinations for standard temperatures at each weight and altitude
within the operational limits for landing.
    Proposed Sec.  23.130 would capture the safety intent of current
Sec.  23.73, Reference landing approach speed, and Sec.  23.75, Landing
Distance. Landing distance information and the associated procedures
for achieving those distances are necessary to prevent runway overruns.
Applicants would be required to determine, develop, and publish
distance and procedures data for use in pilot planning. Proposed Sec.
23.130 would combine the current requirements to determine approach
speed and landing distance because a determination of both is required
for a landing distance determination.
viii. Proposed Sec.  23.200, Controllability
    Proposed Sec.  23.200 would require 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 would
include during low-speed operations, including stalls, with any
probable flight control or propulsion system failure, and during
configuration changes. Proposed Sec.  23.200 would require 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. Proposed Sec.  23.200 would require
VMC not to exceed VS1 or VS0 for all
practical weights and configurations within the operating envelope of
the airplane for certification levels 1 and 2 multiengine airplanes
that cannot climb after a critical loss of thrust. Proposed Sec.
23.200 would also require an applicant to demonstrate those aerobatic
maneuvers for which certification is requested and determine entry
speeds.
    Proposed Sec.  23.200 would capture the safety intent of Sec. Sec.
23.141, Flight Characteristics--General, 23.143, Controllability and
Maneuverability--General; 23.145, Longitudinal control; 23.147
Directional and lateral control; 23.149, Minimum control speed; 23.151,
Acrobatic maneuvers; 23.153, Control during landing; 23.155, Elevator
control force in maneuvers; 23.157, Rate of roll; 23.697(b) and (c),
Wing flap controls. Proposed Sec.  23.200 would ensure the maneuvering
flight characteristics of the airplane are safe and predictable
throughout the flight envelope and result in repeatable, smooth
transitions between turns, climbs, descents, and level flight.
Configuration changes, such as flap extension and retraction, landing
gear extension and retraction, and spoiler extension and retraction,
along with probable failures resulting in asymmetric thrust, would also
have to result in safe, controllable, and predictable characteristics.
    Proposed Sec.  23.200(a) and (b) would capture the safety intent of
Sec. Sec.  23.143, Controllability and Maneuverability--General;
23.145, Longitudinal control; 23.147, Directional and lateral control;
23.149, Minimum control speed; 23.151, Acrobatic maneuvers; 23.153,
Control during landings; 23.155, Elevator control force in maneuvers;
and 23.157, Rate of roll. The FAA proposes limiting the requirements
for practical loadings and operating altitudes without the use of
exceptional piloting skill, alertness, or strength.
    Current part 23 provides prescriptive and detailed test
requirements based on specific airplane configurations. Additionally,
the current rules include flight test procedures that are based on
traditional reversible controls and engine locations that are, in some
cases, derived from airplanes designed in the 1930's. The FAA proposes
performance-based requirements that would remain applicable to
traditionally designed airplanes, but allow alternative approaches to
showing compliance based on new configurations, flight control systems,
engine locations, and number of engines.
    Proposed Sec.  23.200(c) would require all certification levels 1
and 2 multiengine airplanes that lack the performance to climb after a
critical loss of thrust to stall before loss of directional control.
This is a new requirement and it targets the high number of fatal
accidents that occur after an engine failure in this class of airplane.
Light multiengine airplanes that lack the performance to climb after
the critical loss of thrust are especially susceptible to this type of
accident. The Part 23 Reorganization ARC discussed and several members
proposed that all multiengine airplanes have guaranteed climb
performance after a critical loss of thrust. Ultimately, this approach
was rejected, as it could impose a significant cost on the production
of training airplanes. Furthermore, several members pointed out that
the safety concern was not that the airplane could not climb on one
engine, but rather that the airplane would depart controlled flight at
low speeds above stall as a result of asymmetric thrust. The FAA agrees
that loss of control caused by asymmetric thrust is the critical safety
issue that should be addressed and the FAA believes that the proposed
rule responds to this concern.

    The FAA recognizes concerns regarding the proposed requirement--if
the airplane is allowed to stall, the asymmetric thrust will still
cause the airplane to lose directional control and likely depart
controlled flight. The FAA agrees, but believes that pilots are
typically more aware of their stall speeds than minimum control speed,
especially during turns. Furthermore, these airplanes would be required
to meet the proposed stall warning and stall characteristic
requirements, which the FAA expects would provide additional safety
margins beyond current requirements. Finally, the system that provides
stall warning could also be designed to provide VMC warning.
ix. Proposed Sec.  23.205, Trim
    Proposed Sec.  23.205 would require 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.
    Proposed Sec.  23.205 would capture the safety intent of current
Sec.  23.161, Trim. Section 23.161(a) addresses the safety intent while
paragraphs (b), (c), (d), and (e) provide prescriptive details on how
to do flight testing for traditionally configured airplanes and are
more appropriate for inclusion in means of compliance.
x. Proposed Sec.  23.210, Stability
    Proposed Sec.  23.210 would require airplanes not certified for
aerobatics to have static and dynamic longitudinal, lateral, and
directional stability in normal operations, and provide stable control
force feedback throughout the operating envelope. Proposed Sec.  23.210
would also preclude 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.
    Proposed Sec.  23.210 would capture the safety intent of the
current Sec. Sec.  23.171, Stability--General; 23.173, Static
longitudinal stability; 23.175, demonstration of static longitudinal
stability; 23.177, Static directional and lateral stability; 23.179,
Instrumented stick force measurements; and 23.181, Dynamic stability.
The current requirements have their origins in Aeronautics Bulletin 7,
amendment 7a, effective October 1, 1934, which predates CAR 3. These
airplane handling quality and stability requirements were based on the
technology associated with simple mechanical control systems and what
was considered acceptable on existing airplanes of the time. Although
many of these requirements are still appropriate for traditional flight
control systems, they do not take into account the capabilities of new
computer-based flight control systems. The FAA recognizes the
availability of hybrid reversible and automated flight control systems
and proposes performance-based language that would allow their
installation in part 23 certificated airplanes without the use of
special conditions, while still maintaining adequate requirements for
reversible controls. The intent is to facilitate the use of systems
that may enhance safety while reducing pilot workload.
xi. Proposed Sec.  23.215, Stall Characteristics, Stall Warning, and
Spins
    Proposed Sec.  23.215 would require an airplane to have
controllable stall characteristics in straight flight, turning flight,
and accelerated turning flight with a clear and distinctive stall
warning that would provide sufficient margin to prevent inadvertent
stalling. Proposed Sec.  23.215 would allow for alternative approaches
to meeting this requirement for certification levels 1 and 2 airplanes
and certification 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 require 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.
Additionally, the airplane would not be allowed to exceed 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 preclude 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.
    Proposed Sec.  23.215 would capture the safety intent of current
Sec. Sec.  23.201, Wings level stall; 23.203, Turning flight and
accelerated turning stalls; 23.207, Stall warning; and 23.221,
Spinning. Historically, the FAA focused its requirements on the ability
of the airplane to recover from a one-turn or three-second spin more
than on the stall characteristics of the airplane. From the first fatal
stall accident in the Wright Flyer airplane to today's fatal stall
accidents, the number one cause in small airplanes is a departure from
controlled flight following an inadvertent stall.
    Except for accidental departures from controlled flight during
stall training, most of these inadvertent departures occur in close
proximity to the ground, and because of this, the current requirement
to recover from a one-turn or three-second spin may not be the best
method to assess the safety of the airplane. Even an experienced pilot
may not have enough altitude to recover from the spin before impacting
the ground. For this reason, the FAA proposes to delete the one-turn/
three-second spin recovery requirement for normal category airplanes.
Instead, the FAA proposes to increase the stall characteristics
requirements by requiring that all certification levels 1 and 2
airplanes and certification level 3 single-engine airplanes provide
substantial departure resistance to prevent inadvertent stalls from
resulting in a departure from controlled flight and becoming fatal
accidents.
    Accident studies show that even hitting the ground as a result of a
stall can be survivable if the airplane is still in controlled flight.
Conversely, impacting the ground out of control is typically fatal. The
FAA envisions numerous alternative approaches to meeting the proposed
requirements, ranging from one extreme of spin resistance to the other
extreme of a total systems-based approach such as stick pusher.
Furthermore, there are envelope protection systems and stall warning
concepts that could also be considered when assessing departure
resistance. The possible approaches to meeting the proposed
requirements are so broad that these alternatives would be better
addressed in means of compliance. This level of protection may vary
based on the characteristics of the airplane, but the FAA expects this
change in design philosophy would increase the level of protection
designed into airplanes under this proposed rule. Certification level 3
multiengine airplanes and certification level 4 airplanes historically
have not had a large number of departure-related accidents. While the
FAA encourages manufacturers to consider designing departure resistance
into these airplanes, the FAA does not propose adding a new requirement
for certification level 3 multiengine airplanes and certification level
4 airplanes.
    The FAA also proposes revising stall warning requirements by
removing prescriptive speed based stall warning requirements and
requiring a clear and distinctive warning with sufficient

warning margin for the pilot to prevent a stall. Historically, stall
warning systems in part 23 airplanes have been simple, mechanical vanes
that may or may not provide reasonable lead-time to prevent a stall.
These systems also can provide false alerts when they are not needed,
creating a nuisance. Furthermore, similar sounding warning horns that
alert the pilot of other situations can result in the pilot either
becoming used to the warning sounds or mistaking the stall warning for
another warning such as the autopilot disconnect horn. The FAA believes
removing the current prescriptive speed based stall warning from the
rules would encourage the installation of better, more effective low
speed awareness systems that may use angle of attack, a speed decay
rate, or clear voice commands to alert the pilot.
xii. Proposed Sec.  23.220, Ground and Water Handling Characteristics
    Proposed Sec.  23.220 would require airplanes intended for
operation on land or water to have controllable longitudinal, and
directional handling characteristics during taxi, takeoff, and landing
operations. Proposed Sec.  23.220 would also require an applicant to
establish a maximum wave height shown to provide for controllable
longitudinal, and directional handling characteristics and any
necessary water handling procedures for those airplanes intended for
operation on water.
    Proposed Sec.  23.220 would capture the safety intent of Sec. Sec.
23.231, Longitudinal stability and control; 23.233, Directional
stability and control; 23.235, Operation on unpaved surfaces; 23.237,
Operation on water; and 23.239, Spray characteristics.
xiii. Proposed Sec.  23.225, Vibration, Buffeting, and High-Speed
Characteristics
    Proposed Sec.  23.225 would preclude vibration and buffeting from
interfering with the control of the airplane or causing fatigue to the
flightcrew, for operations up to VD/MD. Proposed
Sec.  23.225 would allow stall warning buffet within these limits.
Proposed Sec.  23.225 would preclude perceptible buffeting in cruise
configuration at 1g and at any speed up to VMO/
MMO, except stall buffeting for high-speed airplanes and all
airplanes with a maximum operating altitude greater than 25,000 feet
(7,620 meters) pressure altitude. Proposed Sec.  23.225 would require
an applicant seeking certification of a high-speed airplane to
determine the positive maneuvering load factors at which the onset of
perceptible buffet occurs in the cruise configuration within the
operational envelope and preclude likely inadvertent excursions beyond
this boundary from resulting in structural damage. Proposed Sec.
23.225 would also require high-speed airplanes to have recovery
characteristics that do not result in structural damage or loss of
control, beginning at any likely speed up to VMO/
MMO, following an inadvertent speed increase and a high-
speed trim upset.
    Proposed Sec.  23.225 would capture the safety intent of current
Sec. Sec.  23.251, Vibration and buffeting; 23.253, High speed
characteristics; and 23.255, Out of trim characteristics. Proposed
Sec.  23.225(a), (b), and (c) would capture the safety of current Sec.
23.251(a), (b), and (c). The current safety intent of Sec. Sec.  23.253
and 23.255 are incorporated in proposed Sec.  23.225(d).
    Proposed Sec.  23.225(d)(1) addresses the current language in Sec.
23.253, which indirectly divides the airplanes by engine type rather
than performance. These requirements have typically been applied
automatically to turbine-powered airplanes with the assumption that all
turbine-powered airplanes flew fast and high. Piston or electric
airplanes were not required to meet these requirements even if they
were faster than many turboprops, because of propulsion assumptions in
the past. For this reason, the FAA is amending this requirement to be
based on performance instead of propulsion type using the same high-
speed criteria from other subpart B sections. The existing details
would be removed from the rules, as they are more appropriate as means
of compliance because it would allow for alternatives for non-
traditional airplanes, such as very fast piston airplanes.
    Proposed Sec.  23.225(d)(2) would address the current safety intent
in Sec.  23.255 by relying on performance and design characteristics
without discriminating based on propulsion type. The specific design
details are more appropriate as means of compliance.
xiv. Proposed Sec.  23.230, Performance and Flight Characteristics
Requirements for Flight in Icing Conditions
    Proposed Sec.  23.230 would require an applicant requesting
certification for flight in icing conditions to demonstrate compliance
with each requirement of this subpart. Exceptions to this rule would be
those applicable to spins and any requirement that would have to be
demonstrated at speeds in excess of 250 KCAS, VMO or
MMO, or a speed that an applicant demonstrates the airframe
would be free of ice accretion. Proposed Sec.  23.230 would require the
stall warning for flight in icing conditions and non-icing conditions
to be the same. Proposed Sec.  23.230 would require an applicant
requesting certification for flight in icing conditions to provide a
means to detect any icing conditions for which certification is not
requested and demonstrate the airplane's ability to avoid or exit those
conditions. Proposed Sec.  23.230 would also require an applicant to
develop an operating limitation to prohibit intentional flight,
including takeoff and landing, into icing conditions for which the
airplane is not certified to operate. Proposed Sec.  23.230 would also
increase safety by adding optional icing conditions a manufacturer may
demonstrate its airplane can either safely operate in, detect and
safely exit, or avoid. Proposed Sec.  23.230 would only apply to
applicants seeking certification for flight in icing.
    Proposed Sec.  23.230 would capture the safety intent of the
performance and flight characteristics requirements in current Sec.
23.1419(a) and along with proposed Sec. Sec.  23.940, Powerplant ice
protection, and 23.1405, Flight in icing conditions, and their
respective means of compliance would address NTSB safety
recommendations A-96-54 and A-96-56. Section 23.1419 specifies that
airplanes must be able to operate safely in the icing conditions
identified in appendix C to part 25, which encompass cloud size drops
of less than 100 microns in diameter. Freezing drizzle (i.e., drops up
to 500 microns in diameter) and freezing rain (i.e., drops greater than
500 microns in diameter) icing conditions, which can result in ice
accretion aft of leading edge ice protection systems, are not included
in appendix C to part 25. Amendment 25-140 (79 FR 65507, November 4,
2014) added these icing conditions to appendix O to part 25 and are not
being defined in proposed Sec.  23.230. The FAA believes that the
definitions of these optional icing conditions would be more
appropriate as a means of compliance. The standards for ``capable of
operating safely'' in these conditions would be the same as cloud icing
with additional icing conditions in the takeoff phase.
    If certification for flight in the optional freezing drizzle or
freezing rain conditions is not sought, proposed Sec.  23.230 would
require these conditions be avoided or detected and exited safely. The
means of compliance for the latter, detect and exit the situation,
would be similar to current guidance in AC 23.1419-2D, Certification of
Part 23 Airplanes for Flight in Icing Conditions, and is currently
applied during part 23

airplane icing certifications. These criteria are not as extensive as
recommended by the Part 23 Icing ARC, but the FAA did not want to
impose an additional burden on industry because the service history of
airplanes certified under part 23 and the latest icing regulations at
amendment 23-43 (58 FR 18958, April 9, 1993) show no SLD related
accidents. The FAA believes the safety of the existing fleet can be
greatly increased by improving the freezing drizzle and freezing rain
capability of automated surface weather observation systems and pilot
education and training of the limits of icing certification.
    Proposed Sec.  23.230(b) would provide an option to avoid, in lieu
of detecting and exiting, the freezing drizzle or freezing rain icing
conditions for which the airplane is not certified. This option is not
in current guidance and such technology currently does not exist. The
rule would provide an option in the event the technology is developed.
The FAA believes avoiding rather than detecting and exiting would
provide for safer airplane operations and reduce certification costs.
    Proposed Sec.  23.230(c) would require an AFM limitation to
prohibit flight in icing conditions for which the airplane is not
certified. This reflects current guidance in AC 23.1419-2D, which most
manufacturers of new part 23 icing certified airplanes follow today. A
minority of new manufacturers are not using AC 23.1419-2D guidance and
have inserted AFM limitation language that reflects Airworthiness
Directives (AD) that were issued globally to pneumatic boot-equipped
airplanes between 1996 and 1998. The ADs in the below table require
immediate exit from severe icing and warn that freezing drizzle and
freezing rain may be conducive to severe icing. The proposed new
limitation is intended to prohibit flight in known icing conditions,
not forecast conditions.

------------------------------------------------------------------------
             Airplane model                   Docket        Final rule
------------------------------------------------------------------------
Aerostar Aircraft Corporation Models PA-     97-CE-56-AD        98-04-23
 60-600, PA-60-601, PA-60-601P, PA-60-
 602P, and PA-60-700P Airplanes.........
Pilatus Britten-Norman Ltd., Models BN-      97-CE-54-AD        98-04-21
 2A, BN-2B, and BN-2T Airplanes.........
Pilatus Aircraft Ltd., Models PC-12 and      97-CE-53-AD        98-20-28
 PC-12/45 Airplanes.....................
Partenavia Costruzioni Aeronauticas,         97-CE-51-AD        98-04-20
 S.p.A. Model P68, AP68TP 300, AP68TP
 600 Airplanes..........................
Mitsubishi Heavy Industries, Ltd., MU-2B     96-CE-61-AD        96-25-02
 Series Airplanes.......................
Harbin Aircraft Manufacturing Corp.,         97-CE-50-AD        98-04-19
 Model Y12 IV airplanes.................
Empresa Brasileira de Aeronautica S.A.       96-CE-02-AD        96-09-12
 Airplanes. (Embraer) Models EMB-110P1
 and EMB-110P2 Airplanes................
Dornier Luftfahrt GmbH, 228 Series           96-CE-04-AD        96-09-14
 Airplanes..............................
De Havilland, Inc., DHC-6 Series             96-CE-01-AD        96-09-11
 Airplanes..............................
The Cessna Aircraft Company, 208 Series.     96-CE-05-AD        96-09-15
The Cessna Aircraft Company, Model T210R     98-CE-19-AD        98-20-33
 airplane...............................
The Cessna Aircraft Company, Models          97-CE-62-AD     98-05-14 R1
 T210, P210, P210R airplanes............
The Cessna Aircraft Company Models T303,     97-CE-63-AD        98-04-28
 310R, T310R, 335, 340A, 402B, 402C,
 404, F406, 414, 414A, 421B, 421C, 425,
 and 441 Airplanes......................
Jetstream Aircraft Limited Models 3101       96-CE-07-AD        96-09-17
 and 3201 Airplanes.....................
The New Piper Aircraft PA-23, PA-30, PA-     98-CE-77-AD        99-14-01
 31, PA-34, PA-39, PA-40, and PA-42
 Series Airplanes.......................
The New Piper Aircraft Corporation           97-CE-60-AD        98-04-26
 Models PA-46-310P and PA-46-350P
 Airplanes..............................
Beech Aircraft Corporation Models 99,        96-CE-03-AD        96-09-13
 99A, A99A, B99, C99, B200, B200C, 1900,
 1900C, and 1900D Airplanes.............
Raytheon Aircraft Company 200 Series         98-CE-17-AD        98-20-38
 Airplanes..............................
Raytheon Aircraft Company Models E55,        97-CE-58-AD        98-04-24
 E55A, 58, 58A, 58P, 58PA, 58TC, 58TCA
 Airplanes, and 60, 65-B80, 65-B90, 90,
 F90, 100, 300, and B300 Series
 Airplanes..............................
Raytheon Aircraft Company Model 2000         97-CE-59-AD        98-04-25
 Airplanes..............................
AeroSpace Technologies Of Australia Pty      97-CE-49-AD        98-04-18
 Ltd., Models N22B and N24A.............
SIAI Marchetti, S.r.1 Models SF600 and       97-CE-64-AD        98-05-15
 SF600A Airplanes.......................
SOCATA--Groupe AEROSPATIALE, Model TBM       97-CE-55-AD        98-04-22
 700 Airplanes..........................
Twin Commander Aircraft Corporation          97-CE-57-AD        98-20-34
 Models 500, 500-A, 500-B, 500-S, 500-U,
 520, 560, 560-A, 560-E, 560-F, 680, 680-
 E, 680FL(P), 680T, 680V, 680W, 681,
 685, 690, 690A, 690B, 690C, 690D, 695,
 695A, 695B, and 720 Airplanes..........
Fairchild Aircraft Corporation, SA226        96-CE-06-AD        96-09-16
 and SA227 Series Airplanes.............
------------------------------------------------------------------------

    Recently, manufacturers of airplanes certificated under part 23
have proposed inhibiting, or optimizing, bleed air ice protection
systems above an altitude of 30,000 feet (9,144 meters) because the
icing conditions defined in the appendix C to part 25 are limited to
below this altitude. The FAA believes ice protection design at high
altitude should be addressed as a means of compliance and not in the
proposed rule due to various acceptable design solutions. An industry
means of compliance would negate the need for a special condition or
means of compliance issue paper currently required for these projects.
xv. Current Subpart B Regulations Relocated to Other Proposed Subparts
    The FAA proposes addressing the safety intent of Sec.  23.33,
Propeller speed and pitch limits, in Sec.  23.900(a) of the propulsion
rules. Additionally, the first part of the current Sec.  23.251(a) that
addresses structural damage has been relocated and is now addressed
under ``flutter'' in proposed subpart C to part 23.
    The FAA proposes adopting the Part 23 Icing and Part 23
Reorganization ARC's recommendations to move performance and flight
characteristics requirements in icing, currently in Sec.  23.1419, to
subpart B, so that proposed Sec.  23.1405 only contains systems
requirements. Proposed Sec.  23.230(a) would also include stall warning
requirements. Current guidance contains these stall warning
recommendations (i.e., margin and type of stall) and service history
shows them to be necessary for safe flight in icing conditions. The
exceptions for spin and high-speed requirements are consistent with the
current rule and industry practice that have shown to provide an
adequate level of safety in icing conditions. The FAA determined that
the evaluations of ice contaminated tailplane stall susceptibility,
lateral control in icing, and autopilot operation in icing, which are
included in current guidance for part 23 icing certification,

are more appropriately addressed as a means of compliance.
xvi. Removal of Subpart B Current Regulations
    The FAA proposes removing Sec.  23.45(g) that requires takeoff and
landing distances be determined on a smooth, dry, hard-surfaced runway.
The FAA believes that most performance tests would be done on smooth,
dry, hard-surfaced runways because these surfaces provide applicants
with the best results. Performance determinations on surfaces other
than smooth, dry hard surfaces would provide conservative results and
be acceptable as long as the surface was specified in the AFM.
Therefore, the FAA believes retaining this requirement is unnecessary.
    The FAA proposes removing Sec.  23.63, Climb: General, which
addresses the general climb requirements, because the safety intent
contained in this section is redundant with the safety intent proposed
in Sec.  23.125 and the testing procedures contained in Sec.  23.63 are
more appropriate for inclusion in means of compliance.
    The FAA proposes removing current Sec.  23.221(a) and (b), which
address spinning requirements for normal and utility category
airplanes, and would no longer be necessary. The increased focus on
preventing stall-based departures along with improved stall margin
awareness would provide a level of safety higher than would be achieved
through spin testing.
    The FAA proposes removing the reference to appendix C to part 25,
part II, currently in Sec.  23.1419, Ice protection, paragraph (a),
when relocating Sec.  23.1419 to proposed Sec.  23.230 and 23.1405.
Part II is a means of compliance for determining critical ice
accretions on transport category airplanes and is not applicable to
airplanes certified under part 23.
3. Subpart C--Structures
a. General Discussion
    The FAA's intent in proposed subpart C is to provide a regulatory
framework that maintains the current level of safety while (1) allowing
for certification of unique airplane configurations with new technology
and materials, and (2) supporting new means of compliance, testing, and
analysis. To support new technologies, the FAA proposes to incorporate
the safety intent of recent special conditions for airplanes equipped
with systems that affect structural performance, such as load
alleviation systems, in proposed Sec.  23.305. To support new means of
compliance, the FAA proposes in Sec.  23.600 to emphasize a holistic
approach to occupant safety, which would allow certain applicants to
omit current required dynamic seat testing.
    It is not the FAA's intent to reduce the level of safety in the
proposed subpart C. The FAA based the prescriptive requirements in
current subparts C and D on service history, historic test data, and
lessons learned. These requirements have provided a level of safety
where structural failure is rare and most often attributable to
airplane upset or pilot disorientation in instrument meteorological
conditions. A means of compliance to proposed subpart C must maintain
the level of safety provided by the current regulations. Applicants
would need to substantiate the level of safety for proposed means of
compliance that deviate from the prescriptive regulations.
    Proposed subpart C would replace current subpart C and include
those sections of current subpart D that are applicable to the
airframe. We have arranged proposed subpart C into the following five
topics:

     General: Including Sec.  23.300, Structural design
envelope; and Sec.  23.305 Interaction of systems and structures.
     Structural Loads: Including Sec.  23.310, Structural
design loads; Sec.  23.315, Flight load conditions; Sec.  23.320,
Ground and water load conditions; Sec.  23.325, Component loading
conditions; and Sec.  23.330, Limit and ultimate loads.
     Structural performance: Including Sec.  23.400,
Structural strength; Sec.  23.405, Structural durability; and Sec.
23.410, Aeroelasticity.
     Design: Including Sec.  23.500, Structural design;
Sec.  23.505, Protection of structure; Sec.  23.510, Materials and
processes; and Sec.  23.515, Special factors of safety.
     Structural occupant protection: Included in Sec.
23.600, Emergency conditions.

    The FAA proposes removing the content of current appendix A to part
23, Simplified design load criteria; appendix C to part 23, Basic
landing conditions; appendix D to part 23, Wheel spin-up and spring-
back loads; and appendix I to part 23, Seaplane loads. The content of
these current part 23 appendices is more appropriate for inclusion in
means of compliance. The FAA also proposes removing appendix B to part
23, Reserved, since the content of this appendix was removed at
amendment 23-42 (56 FR 344, January 3, 1991). Refer to appendix 1 of
this preamble for a cross-reference table detailing how the current
regulations are addressed in the proposed part 23 regulations.
b. Specific Discussion of Changes
i. Proposed Sec.  23.300, Structural Design Envelope
    Proposed Sec.  23.300 would require an applicant to determine the
structural design envelope, which describes the range and limits of
airplane design and operational parameters for which an applicant would
show compliance with the requirements of this subpart. Proposed Sec.
23.300 would capture the safety intent of current Sec. Sec.  23.321,
Loads--General, paragraphs (b) and (c); 23.333, Flight envelope,
paragraphs (a), (b), and (d); 23.335, Design airspeeds; 23.337, Limit
maneuvering load factors, paragraphs (a) and (b); and 23.343, Design
fuel loads, paragraphs (a) and (b).
    Proposed Sec.  23.300 would require the applicant to determine and
document the range of airplane and operational parameters for which the
applicant will show compliance with the requirements of subpart C.
These parameters would include the design airspeeds and maneuver load
factors often depicted as a V-n diagram. An applicant would be required
to determine design airspeeds, including the design maneuvering speed
(VA), the design cruising speed (VC), the design
dive speed (VD), design flap and landing gear speeds, and
any other speed used as a design limitation. For certification of level
4 airplanes, an applicant would be required to determine a rough air
penetration speed, VB.
    Additionally, applicants would have to determine the design
maneuver load factors based on the intended usage of the airplane and
the values associated with the level of safety experienced with current
designs. Applicants have rarely used the relief for maneuvering load
factors based on airplane capabilities in current Sec.  23.337(c). The
FAA views this relief as an application of physical principles, and
believes that this current requirement does not need to be addressed in
proposed Sec.  23.300.
    Design weights and inertia parameters are also part of the
structural design envelope. Design weights include the empty weight,
maximum weight, takeoff and landing weight, and maximum zero fuel
weight. The range of center of gravity locations at these and other
weights is depicted as the weight center of gravity envelope. An
applicant would have to determine the weight and center of gravity of
occupants, payload, and fuel as well as any mass moments of inertia
required for loads or flutter analysis. An applicant would also have to
specify any other parameters that describe the structural design
envelope. These parameters include maximum

altitude limitations, Mach number limitations, and control surface
deflections.
ii. Proposed Sec.  23.305, Interaction of Systems and Structures
    Proposed Sec.  23.305 would provide a regulatory framework for the
evaluation of systems intended to modify an airplane's structural
design envelope or structural performance and other systems whose
normal operating state or failed states may affect structural
performance. Compliance with proposed Sec.  23.305 would provide
acceptable mitigation of structural hazards identified in the
functional hazard assessments required by proposed Sec.  23.1315.
    Proposed Sec.  23.305 would apply to airplanes equipped with--
     Structural systems, including load alleviation systems,
where the intended function is to modify structural performance, to
alleviate the impact of subpart C requirements, or provide a means of
compliance to subpart C requirements; and
     Systems where the intended function is non-structural, but
whose normal operation or failure states affect the structural design
envelope or structural performance, and would include fuel management
systems, flight-envelope protection systems, and active control
systems.
    Under the current regulations, an applicant seeking certification
of airplanes incorporating structural and non-structural systems must
ensure that failures of these systems will not result in exceeding the
structural design envelope or the structural design loads, or other
structural performance characteristics. An applicant has the option of
designing the structure to the full subpart C and subpart D
requirements, including margins of safety, with the system in its
failed state. This option may result in increased structural weight and
reduced airplane performance and utility.
    Proposed Sec.  23.1315 in subpart F would apply to both structural
and non-structural systems. Guidance material for current Sec.
23.1309, the corresponding regulation to proposed Sec.  23.1315, allows
for different acceptable values for likelihood of failures based on the
severity of the hazard, airplane weight, and method of propulsion.
These different values encourage the incorporation of equipment that
improves pilot situational awareness and other systems that promote the
overall airplane level of safety.
    In most cases, means of compliance with proposed Sec.  23.305 would
follow an approach somewhat similar to that used in the guidance
material for current Sec.  23.1309. Structural failures resulting in
fatalities are rare, occurring at a rate of approximately 3 x
10-8 per flight hour for small airplanes. The reason for
incorporating structural systems is not, in general, to improve safety,
but rather to reduce structural weight and thereby improve airplane
performance. Proposed Sec.  23.305 would require that the level of
safety must be the same for airplanes equipped with systems that affect
the structure and airplanes without such systems.
    An existing acceptable means of complying with proposed Sec.
23.305 is provided in several existing special conditions that address
the interaction of systems and structures, for example, FAA Special
Condition 25-390-SC.\20\ Most of these special conditions address load
alleviation systems. Load alleviation systems counteract the effects of
gust and maneuver loads and allow an applicant to design a lighter
structure, thereby improving the performance and utility of the
airplane. These special conditions require that an applicant design the
structure to the required structural safety margins with the load
alleviation system its normal functioning state. The special conditions
provide a means for an applicant to maintain the required structural
safety margins with the system in its failed state by adjusting the
required safety margins based on the likelihood of system failure.
Systems that fail frequently require higher safety margins than systems
that rarely fail in order to maintain the same level of safety. The
means of compliance described in these special conditions allow an
applicant to utilize the benefits of structural systems and potentially
eliminate weight and performance penalties associated with structural
hazards due to system failures.
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    Applicants who use the means of compliance described in the
existing special conditions would be able to use data developed for
compliance with proposed Sec.  23.1315. This data includes
identification of failure modes, identification of hazards resulting
from the failure modes, and the likelihood of the occurrence of the
failure modes. With or without the proposed Sec.  23.305 requirements,
an applicant would have to account for structural performance with the
system in its normal operating and failed states and evaluate the
system for compliance to the proposed Sec.  23.1315. The FAA does not
expect that additional detailed structural analysis would be required
for compliance with proposed Sec.  23.305 other then the application of
optional lower safety margins to the structural performance analysis.
    Proposed Sec.  23.305 would allow an applicant to realize the value
of structural and non-structural systems and would potentially allow
reduced structural weight of the airplane. The magnitude of the weight
reduction would depend on the functional characteristics of the systems
and the likelihood of system failures. The FAA believes proposed Sec.
23.305 would reduce the need for special conditions that deal with
interaction of systems and structures, saving time and effort for the
FAA and the applicant.
iii. Proposed Sec.  23.310, Structural Design Loads
    Proposed Sec.  23.310 would require an applicant to determine
structural design loads resulting from any externally or internally
applied pressure, force, or moment, which may occur in flight, ground
and water operations, ground and water handling, and while the airplane
is parked or moored. Proposed Sec.  23.310 would require the applicant
to determine structural design loads at all combinations of parameters
on and within the boundaries of the structural design envelope which
result in the most severe loading conditions. Proposed Sec.  23.310
would also require the magnitude and distribution of these loads to be
based on physical principles and would be no less than service history
has shown can occur within the structural design envelope.
    Proposed Sec.  23.310 would capture the safety intent of Sec. Sec.
23.301, Loads; 23.302, Canard or tandem wing configurations; 23.321,
Flight Loads--General, paragraph (a); and 23.331, Symmetrical flight
conditions. Proposed Sec.  23.310 would also capture the intent of
several current requirements for sound and physics-based engineering
evaluations. An example is in current Sec.  23.301(b), which requires
that the forces and moments applied to the airplane must balance in
equilibrium, and the distribution of loads on the airplane must
reasonably approximate actual conditions. The part 23 regulations
should not need to prescribe basic physical principles, sound
engineering judgment, and common sense. Proposed Sec.  23.310 would
place the burden on the applicant to properly account for loads acting
on the structure.

iv. Proposed Sec.  23.315, Flight Load Conditions
    Proposed Sec.  23.315 would require an applicant to determine the
loads resulting from vertical and horizontal atmospheric gusts,
symmetric and asymmetric maneuvers, and, for multiengine airplanes,
failure of the powerplant unit which results in the most severe
structural loads. Proposed Sec.  23.315 would capture the safety intent
of current Sec. Sec.  23.333, Flight envelope, paragraph (c); 23.341,
Gust loads factors; 23.347, Unsymmetrical flight conditions; 23.349,
Rolling conditions; 23.351, Yawing conditions; 23.367, Unsymmetrical
loads due to engine failure; 23.421, Balancing loads; 23.423,
Maneuvering loads; 23.425, Gust loads; 23.427, Unsymmetrical loads;
23.441, Maneuvering loads; 23.443, Gust loads; and 23.445, Outboard
fins or winglets, paragraphs (b), (c), and (d).
    These current part 23 sections establish prescriptive requirements
for gust loads and symmetrical, rolling, and yawing maneuvering loads,
acting on the wing, horizontal tail, vertical tail, and other lifting
surfaces. Portions of the current sections, such as Sec.  23.331(c),
are restatements of basic physical principles. Proposed Sec.  23.315
would remove this language.
    The FAA's intent is not to lessen the structural load requirements.
The current prescriptive flight load requirements have established a
level of safety where structural failure due to overloading is rare.
When structural failures do occur, the most common cause is airplane
upset or pilot disorientation in instrument meteorological conditions.
    The FAA believes the prescriptive content of the current
regulations, including the modified Pratt formula for gust loads, the
descriptions of symmetrical maneuvers, checked and unchecked maneuvers,
rolling maneuvers, and yawing maneuvers are more appropriate for
inclusion in means of compliance. Applicants who wish to propose
alternate design loading conditions should note that extensive data
collection, testing, and evaluation may be necessary to substantiate
their proposal.
v. Proposed Sec.  23.320, Ground and Water Load Conditions
    Proposed Sec.  23.320 would require an applicant to determine the
loads resulting from taxi, take-off, landing, and ground handling
conditions occurring in normal and adverse attitudes and
configurations. Proposed Sec.  23.320 would capture the safety intent
of current Sec. Sec.  23.471, Ground Loads--General; 23.473, Ground
load conditions and assumptions; 23.477, Landing gear arrangement;
23.479, Level landing conditions; 23.481, Tail down landing conditions;
23.483, One-wheel landing conditions; 23.485, Side load conditions;
23.493, Braked roll conditions; 23.497, Supplementary conditions for
tail wheels; 23.499, Supplementary conditions for nose wheels; 23.505,
Supplementary conditions for skiplanes; 23.507, Jacking loads; 23.509,
Towing loads; 23.511, Ground load; unsymmetrical loads on multiple-
wheel units; 23.521, Water load conditions; 23.523, Design weights and
center of gravity positions; 23.525, Application of loads; 23.527, Hull
and main float load factors; 23.529 Hull and main float landing
conditions; 23.531, Hull and main float takeoff condition; 23.533, Hull
and main float bottom pressures; 23.535, Auxiliary float loads; 23.537,
Seawing loads, and 23.753 Main float design.
    The current requirements set forth prescriptive requirements for
determining takeoff and landing loads for airplanes operated on land,
loads acting on floats and hulls for airplanes operated on water, as
well as ground handling loads, including jacking and towing conditions.
The current requirements also provide applicants with descriptions of
the normal and adverse operating conditions and configurations for
which applicants must determine ground and water loads.
    The FAA believes that the prescriptive descriptions of the loading
conditions, normal and adverse conditions, and configurations are more
appropriate for inclusion in means of compliance. Applicants who wish
to propose alternate design loading conditions should note that
extensive data collection, testing, and evaluation may be necessary to
substantiate their proposal.
vi. Proposed Sec.  23.325, Component Loading Conditions
    Proposed Sec.  23.325 would require an applicant to determine the
loads acting on each engine mount, flight control and high lift
surface, and the loads acting on pressurized cabins. Proposed Sec.
23.325 would capture the safety intent of current Sec. Sec.  23.345,
High lift devices; 23.361, Engine torque; 23.363, Side load on engine
mount; 23.365, Pressurized cabin loads; 23.371, Gyroscopic and
aerodynamic loads; 23.373, Speed control devices; 23.391, Control
surface loads; 23.393, Loads parallel to hinge line; 23.395, Control
system loads; 23.397, Limit control forces and torques; 23.399, Dual
control system; 23.405, Secondary control system; 23.407, Trim tab
effects; 23.409, Tabs; 23.415, Ground gust conditions; 23.455,
Ailerons; and 23.459, Special devices.
    The current part 23 regulations establish prescriptive requirements
for determining loads acting on pressurized cabins, engine mounts and
attachment structure, control surfaces, high lift surfaces, and speed
control devices. The FAA believes that these prescriptive requirements
in the current regulations are more appropriate for inclusion in means
of compliance. However, in proposed Sec.  23.325, we have retained some
of the prescriptive requirements for pressurized cabins, including
descriptions of combined loading conditions and additional factors of
safety for determining limit load.
vii. Proposed Sec.  23.330, Limit and Ultimate Loads
    Proposed Sec.  23.330 would describe how the applicant must
determine the limit and ultimate loads associated with the structural
design loads. Proposed Sec.  23.330 would capture the safety intent of
current Sec. Sec.  23.301, Loads, paragraph (a); and 23.303, Factor of
safety. These current sections specify factors of safety for
determining limit and ultimate loads.
    Proposed Sec.  23.330 retains the current 1.5 safety factor for
ultimate loads. This safety factor has resulted in a service history
where structural failures due to applied static loads are rare. The FAA
believes the 1.5 factor of safety is critical to maintaining the
current level of safety.
    Proposed Sec.  23.330 would allow for additional special factors of
safety to account for material and manufacturing variability. Proposed
Sec.  23.330 would also allow alternate factors of safety when showing
compliance with occupant protection loading conditions and when showing
compliance with proposed Sec.  23.305.
viii. Proposed Sec.  23.400, Structural Strength
    Proposed Sec.  23.400 would require an applicant to demonstrate
that the structure will support limit and ultimate loads. Proposed
Sec.  23.400 would capture the safety intent of current Sec. Sec.
23.305, Strength and deformation; and 23.307, Proof of structure.
    These current sections provide performance criteria for the
structure when subjected to limit and ultimate loads. Proposed Sec.
23.400 would retain these performance criteria and would require the
applicant to demonstrate that the structure will meet these performance
criteria. In this context, ``demonstrate'' means the applicant must
conduct structural tests to show

compliance with the structural performance requirements, unless the
applicant shows that a structural analysis is reliable and applicable
to the structure. The FAA proposes not to retain the ``3 second'' rule
in proposed Sec.  23.400. This prescriptive requirement in current
Sec.  23.305(b) requires the applicant to demonstrate that the
structure will support ultimate load for at least three seconds. The
FAA believes this prescriptive requirement is a statement of physical
principles and testing experience and is more appropriate for inclusion
in means of compliance.
ix. Proposed Sec.  23.405, Structural Durability
    Proposed Sec.  23.405 would require an applicant to develop and
implement procedures to prevent structural failures due to foreseeable
causes of strength degradation, and to prevent rapid decompression in
airplanes with a maximum operating altitude above 41,000 feet. Proposed
Sec.  23.405 would also require an airplane to be reasonably capable of
continued safe flight and landing with foreseeable structural damage
caused by high-energy fragments from an uncontained engine or rotating
machinery failure. Proposed Sec.  23.405 would capture the safety
intent of current Sec. Sec.  23.365(e), Pressurized cabin loads;
23.571, Metallic pressurized cabin structures; 23.572, Metallic wing,
empennage, and associated structures; 23.573, Damage tolerance and
fatigue evaluation of structure; 23.574, Metallic damage tolerance and
fatigue evaluation of commuter category airplanes; 23.575, Inspections
and other procedures; and 23.627, Fatigue strength.
    Proposed Sec.  23.405(a) would require an applicant to develop and
implement procedures to prevent structural failures. These procedures
may include the safe-life, damage tolerance, or fail-safe design
approaches described in the current regulations. An applicant can
propose other means of compliance, but these means must provide at
least the same level of safety as current means of compliance. Any new
means of compliance must consider the airplane design, manufacturing,
operational, and maintenance environments. The FAA proposes
implementing these procedures by including them in the airplane's
Instructions for Continued Airworthiness.
    The procedures must be able to prevent structural failures due to
foreseeable causes of strength degradation. Foreseeable causes include
fatigue and corrosion in metallic structures, and fatigue,
delaminations, disbonds, and impact damage in composite structures. New
material systems or structural designs, such as additive manufacturing,
may introduce new causes of strength degradation and may require
development of new and unique procedures to prevent structural
failures.
    The current part 23 regulations use prevention of catastrophic
failures as the safety intent of the regulations. The word
``catastrophic'' is used throughout the current regulations, current
policy, and guidance material, especially in context of system safety
analysis. To avoid any potential conflict over the meaning of
``catastrophic,'' proposed Sec.  23.405(a) would specify the
consequences we want to prevent. These consequences include the obvious
performance criteria for prevention of serious injuries, fatalities, or
hull loss of the airplane.
    The FAA also wants to prevent extended periods of operations with
reduced safety margins in those structural components whose failure
could result in serious injuries, fatalities, or hull loss. One
situation that can result in reduced safety margins is fail-safe
design. The FAA has identified potential shortcomings in fail-safe
designs, including an applicant's difficulty to anticipate all possible
failure scenarios and ensure that all structural failures would be
immediately obvious and corrected before further flight. The concept of
failures being obvious and repaired before further flight is basic to
the successful implementation of a fail-safe design. This scenario
could allow operation for extended periods with a passive structural
failure and reduced safety margins. If an applicant chooses fail-safe
design as a means of compliance, an applicant would have to ensure that
the structure was not operating for extended periods with reduced
safety margins. An applicant may be able to apply safe-life or damage
tolerance principles to ensure that fail-safe structure maintains the
required safety margins without extended periods of operation with
reduced safety margins through life limits or damage tolerance based
inspections.
    Proposed Sec.  23.405(b) would capture the safety intent of current
Sec.  23.365(e), requiring the applicant to design the structure for
sudden loss of pressurization after the failure of a door or window in
pressurized compartments. Proposed Sec.  23.405(c) incorporates the
safety intent of current Sec.  23.571(d). Our intention is that the
damage tolerance methodology would remain the accepted means of
compliance. The FAA views damage tolerance as necessary since current
Sec.  23.571(d) and proposed Sec.  23.405(c) require the applicant to
assume that structural damage exists in the pressurized cabin. However,
proposed Sec.  23.405(c) would allow for other means of compliance as
long as serious injuries and fatalities will be prevented. Examples of
other means of compliance might include requiring pilots and occupants
to use oxygen masks or wear pressurized flight suits when operating
above 41,000 feet (12,497 meters). This means of compliance could be
acceptable in certain airplane designs, such as two-seat jet trainers.
    Proposed Sec.  23.405(d) would capture the safety intent of current
Sec.  23.903(b)(1) to minimize hazards to the airframe resulting from
turbine engine rotorburst. The FAA would move the structural portion of
the rotorburst evaluation from current Sec.  23.903(b)(1) to proposed
Sec.  23.405(d) to ensure all structural requirements are contained in
subpart C and to avoid potential confusion over the structural
rotorburst requirements in part 23.
    Proposed Sec.  23.405(d) would require an applicant to show that
the design of the structure would provide sufficient structural
capability to allow continued safe flight and landing with foreseeable
structural damage caused by high energy fragments from an uncontained
engine or rotating machinery failure. The FAA recognizes that some
high-energy fragment events may result in catastrophic failures that
may not be avoidable and that complete elimination of the hazards
resulting from high energy fragment events may not be possible.
    An applicant would be required to address other sources of high
energy rotating machinery fragments in the proposed structural
rotorburst requirements. Our intent is to ensure an adequate regulatory
framework for applications of electrical propulsion systems and other
unique and novel approaches to propulsion, which may release high-
energy fragments.
    Applicants who have shown compliance with current Sec.
23.903(b)(1) would be able to show compliance with proposed Sec.
23.405(d). Applicants should note that previous certification programs
with turbine engine installations have been able to show that the
airplane structure is capable of continued safe flight and landing
following a rotorburst event. AC 23-13A, Fatigue, Fail-Safe, and Damage
Tolerance Evaluation of Metallic Structure for Normal, Utility,
Acrobatic, and Commuter Category airplanes, provides guidance on the
required structural evaluation.

x. Proposed Sec.  23.410, Aeroelasticity
    Proposed Sec.  23.410 would require an airplane to be free from
flutter, control reversal, and divergence at all speeds within and
sufficiently beyond the structural design envelope, for any
configuration and condition of operation, accounting for critical
degrees of freedom, and any critical failures or malfunctions. Proposed
Sec.  23.410 would also require an applicant to establish tolerances
for all quantities that affect flutter.
    Proposed Sec.  23.410 would capture the safety intent of the
current Sec. Sec.  23.629, Flutter; 23.677, Trim systems, paragraph
(c); and 23.687, Spring devices, in part. Specifically, proposed Sec.
23.410 would address the safety intent of these rules by requiring
freedom from flutter, control reversal, and divergence, while
accounting for all speeds, configurations, modes, and failures, and to
establish tolerances on anything affecting flutter. The current Sec.
23.629(a) states that freedom from flutter, control reversal, and
divergence must be shown by the methods of Sec.  23.629(b) and (c) or
(d). These paragraphs are prescriptive in nature and some portions are
applicable only to very specific types of designs and include speed
limitations. Therefore, these paragraphs are more appropriate as means
of compliance.
    The current Sec.  23.629(e) requires the evaluation of whirl mode
flutter. Since this is another flutter mode, it must be accounted for
when an airplane is determined to be free from flutter. The current
Sec.  23.629(f), (g), (h), and (i) provide instructions on how to
evaluate (1) certain airplane design types, (2) designs employing
certain methods (fail-safe or damage tolerant), or (3) airplanes
incorporating design modifications. The current Sec.  23.677(c)
requires either that the tab be balanced or that the tab controls be
irreversible. Additionally, it requires that irreversible tab systems
have adequate rigidity and reliability. These are very specific design
solutions for ensuring freedom from flutter. The current Sec.  23.687
requires that the reliability of spring devices used in control systems
be established by tests unless its failure would not cause flutter.
This is a method of compliance to ensure freedom from flutter. All of
these current requirements are more appropriate as means of compliance
because they describe how to ensure freedom from flutter, control
reversal, and divergence. They are not the safety intent, but just one
method to achieve the safety intent. As such, they serve only specific
designs utilizing current methods, and may or may not be adequate for
innovative designs or accommodate new analytical methods or testing
techniques.
xi. Proposed Sec.  23.500, Structural Design
    Proposed Sec.  23.500 would require an applicant to design each
part, article, and assembly for the expected operating conditions of
the airplane. Proposed Sec.  23.500 would require the design data to
adequately define the part, article, or assembly configuration, its
design features, and any materials and processes used. Proposed Sec.
23.500 would require an applicant to determine the suitability of each
design detail and part having an important bearing on safety in
operations. Proposed Sec.  23.500 would also require the control system
to be free from--
     Jamming;
     Excessive friction, and
     Excessive deflection when the control system and its
supporting structure are subjected to loads corresponding to the limit
airloads when the primary controls are subjected to the lesser of the
limit airloads or limit pilot forces and when the secondary controls
are subjected to loads not less than those corresponding to maximum
pilot effort.
    Proposed Sec.  23.500 would capture the safety intent of the
current Sec. Sec.  23.601, Design and Construction--General; 23.603,
Materials and workmanship, paragraph (b); 23.671, Control Systems--
General, paragraph (a); 23.683, Operation tests; 23.685, Control system
details; 23.687, Spring devices, in part; and 23.689, Cable systems.
These current requirements explain methods and techniques to ensure an
adequate design. The proposed rule would require an applicant to
produce an adequate design without specifying how. The prescriptive
language within these current sections noted above, are more
appropriate for a means of compliance.
xii. Proposed Sec.  23.505, Protection of Structure
    Proposed Sec.  23.505 would require an applicant to protect each
part of the airplane, including small parts such as fasteners, against
deterioration or loss of strength due to any cause likely to occur in
the expected operational environment. Proposed Sec.  23.505 would
require each part of the airplane to have adequate provisions for
ventilation and drainage and would require an applicant to incorporate
a means into the airplane design to allow for required maintenance,
preventive maintenance, and servicing.
    Proposed Sec.  23.505 would capture the safety intent of the
current Sec. Sec.  23.607, Fasteners; 23.609, Protection of structure;
and 23.611, Accessibility. These current requirements explain methods
and techniques to ensure an adequate design. This proposed rule would
require the applicant to produce an adequate design without specifying
how to accomplish it. The prescriptive language within these current
sections is more appropriate as a means of compliance.
xiii. Proposed Sec.  23.510, Materials and Processes
    Proposed Sec.  23.510 would require an applicant to determine the
suitability and durability of materials used for parts, articles, and
assemblies, the failure of which could prevent continued safe flight
and landing, while accounting for the effects of likely environmental
conditions expected in service. Proposed Sec.  23.510 would require the
methods and processes of fabrication and assembly used to produce
consistently sound structures and, if a fabrication process requires
close control to reach this objective, an applicant would have to
perform the process under an approved process specification.
Additionally, proposed Sec.  23.510 would require an applicant to
justify the selected design values to ensure material strength with
probabilities, account for--
     The criticality of the structural element; and
     The structural failure due to material variability, unless
each individual item is tested before use to determine that the actual
strength properties of that particular item would equal or exceed those
used in the design, or the design values are accepted by the
Administrator.
    Proposed Sec.  23.510 would require a determination of required
material strength properties to be based on sufficient tests of
material meeting specifications to establish design values on a
statistical basis. Proposed Sec.  23.510 would also require an
applicant to determine the effects on allowable stresses used for
design if thermal effects were significant on an essential component or
structure under normal operating conditions.
    Proposed Sec.  23.510 would capture the safety intent of the
current Sec. Sec.  23.605, Fabrication methods and 23.613, Material
strength properties and design values. These current requirements
explain methods and techniques to ensure adequate materials and process
controls. This proposed rule would require the applicant to ensure the
resulting materials and processes are adequate without specifying how.
The prescriptive language within the current

sections is more appropriate as a means of compliance.
xiv. Proposed Sec.  23.515, Special Factors of Safety
    Proposed Sec.  23.515 would require an applicant to determine a
special factor of safety for any critical design value that was
uncertain, used for a part, article, or assembly likely to deteriorate
in service before normal replacement, or subject to appreciable
variability because of uncertainties in manufacturing processes or
inspection methods. Proposed Sec.  23.515 would require an applicant to
determine a special factor of safety using quality controls and
specifications that accounted for each structural application,
inspection method, structural test requirement, sampling percentage,
and process and material control. Proposed Sec.  23.515 would require
an applicant to apply any special factor of safety in the design for
each part of the structure by multiplying each limit load and ultimate
load by the special factor of safety.
    Proposed Sec.  23.515 would capture the safety intent of current
Sec. Sec.  23.619, Special factors; 23.621, Casting factors; 23.623,
Bearing factors; 23.625, Fitting factors; 23.657, Hinges; 23.681(b),
Limit load static test (in part); and 23.693, Joints. These current
requirements explain methods and techniques to ensure adequate special
factors are used and the proposed rule would simply require the
applicant to determine and apply adequate special factors without
specifying what these are. The prescriptive language within the current
sections is more appropriate as a means of compliance.
xv. Proposed Sec.  23.600, Emergency Conditions
    Proposed Sec.  23.600 would require the airplane, even if damaged
in emergency landing conditions, to provide protection to each occupant
against injury that would preclude egress. Proposed Sec.  23.600 would
require the airplane to have seating and restraints for all occupants,
consisting of a seat, a method to restrain the occupant's pelvis and
torso, and a single action restraint release, which meets its intended
function and does not create a hazard that could cause a secondary
injury to an occupant. Proposed Sec.  23.600 would require the airplane
seating, restraints, and cabin interior to account for likely flight
and emergency landing conditions. Additionally, they could not prevent
occupant egress or interfere with the operation of the airplane when
not in use.
    Proposed Sec.  23.600 would require each baggage and cargo
compartment be designed for its maximum weight of contents and for the
critical load distributions at the maximum load factors corresponding
to the determined flight and ground load conditions. Proposed Sec.
23.600 would also require each baggage and cargo compartment to have a
means to prevent the contents of the compartment from becoming a hazard
by impacting occupants or shifting, and to protect any controls,
wiring, lines, equipment, or accessories whose damage or failure would
affect operations.
    Proposed Sec.  23.600 would capture the safety intent of current
Sec. Sec.  23.561, Emergency Landing Conditions--General; 23.562,
Emergency landing dynamic conditions; 23.785, Seats, berths, litters,
safety belts, and shoulder harnesses; and 23.787, Baggage and cargo
compartments. The prescriptive language within these current sections
are more appropriate as a means of compliance, and thus would allow
flexibility for new technology to be available in new part 23 airplanes
in a timely manner.
    Occupant safety for aviation has progressed incrementally over the
years. This has resulted in rulemaking that has enhanced safety for
individual system components, but not in an integrated fashion.
Modeling and analysis techniques have matured to a point that may allow
evaluation of more crash scenarios and crashworthiness components as an
integrated system. The FAA has relied on many industry studies to
develop current occupant safety rules. These studies evaluated
characteristics of actual accidents, full-scale aircraft drop testing,
and dynamic seat testing on a sled. When dynamic seat testing began,
determination of an adequate generic floor impulse that represented a
survivable aircraft crash was established. As an alternative to current
crashworthiness requirements, the proposed rule would allow for
evaluation of the conditions of likely impacts, assessment of vehicle
response, and ultimately, evaluation of occupant reaction to vehicle
impact and vehicle response.
    Technology used in aviation crashworthiness, in a large part, has
come from the automotive industry. The automotive industry has analyzed
crashworthiness components as a system for many years. The automotive
industry generally has a more developed crashworthiness analysis
capability than that used in the aviation industry. This advanced
crashworthiness analysis capability has evolved primarily because of
the--
     Public expectation for automobile safety;
     Higher general public likelihood and exposure to
automobile accidents; and
     High automobile production rates allow for multiple actual
full-vehicle crash tests that result in very accurate crash impulse
data from the outer surface of the vehicle all the way to the occupant.
    Because of these facts, automotive designers know accurate impulses
and the specific vehicle response for impact conditions. Furthermore,
this data can be extrapolated to consider many more accident scenarios.
Automotive safety requirements progressively add new impact scenario
requirements and enhanced impulse magnitudes, thus requiring more
industry innovation. This innovation has enabled rapid advances in
automotive occupant protection systems.
    Automotive safety begins at the outside of the vehicle, evaluating
the entire system's response. In contrast, aircraft manufacturers have
used essentially the same generic designed pulse imparted at the cabin
floor for the last 25 years. The same impulse applies to all GA
airplanes independent of the structure below the cabin floor and the
aircraft's stall speed, unless the stall speed is greater than 61
knots. Determining airplane crashworthiness is a more complex process
than determining automotive crashworthiness because of higher impact
speeds, lighter weight structures, and the effect of the third
dimension of altitude on the aircraft. Dynamic seat testing has
improved crashworthiness in aviation; however, the FAA believes that
newer means of evaluating the full aircraft response to crash
conditions via modeling, newer materials, and new technologies promise
to offer improved features, evaluation, and accuracy that would
facilitate consideration of more crash scenarios and evaluation of more
variables that could improve survivability.
    The NTSB produced a series of reports, called the General Aviation
Crashworthiness Project,\21\ in the 1980s that evaluated over 21,000 GA
airplane crashes that occurred between 1972 and 1981. The NTSB
evaluated airplane orientation, impact magnitudes, and survival rates
and factors on many of these accidents in order to provide information
to support changes in crashworthiness design standards for seating and
restraint systems in GA airplanes. These reports also established

conditions approximating survivable accidents, and categorized factors
that would have the largest impact on safety. These reports further
illuminated the various crashworthiness systems and their respective
impact to overall safety. Amendment 23-36 (53 FR 30802, August 15,
1988), to part 23 referenced these reports for dynamic seats but did
not adopt a systems-approach to evaluating crashworthiness of an
airplane design.
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    \21\ See www.regulations.gov (Docket #FAA-2015-1621).
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    The NTSB reports identified several factors that would enhance
safety. All of these factors working together as a system should result
in a safer airplane. However, the assessment indicated that shoulder
harnesses offer the fastest individual improvement for safety. The FAA
codified the shoulder harnesses requirement in amendments 23-19 (42 FR
20601, June 16, 1977) and 23-32 (50 FR 46872, November 13, 1985), for
newly manufactured airplanes. The FAA also issued policy statement ACE-
00-23.561-01,\22\ Methods of Approval of Retrofit Shoulder Harness
Installations in Small Airplanes, to streamline the process for
retrofitting older airplanes.
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    \22\ See www.regulations.gov (Docket #FAA-2015-1621).
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    Survivable volume is another critical factor to survival.
Survivable volume is the ability of the airframe to protect the
occupants from external intrusion or cabin crushing during and after
the accident sequence. There were several observed accidents in the
NTSB study where conventional aircraft construction simply crushed an
otherwise restrained occupant. Crashworthiness regulations have never
included survivable volume as a factor, except for aircraft turnover.
Airplane designs should provide the space needed for the protection and
restraint of the occupants. A compromised survivable volume could cause
occupant impact with objects in the cabin. This is one of the first
steps in the analysis of airplane crashworthiness.
    Additional data from the NTSB General Aviation Crashworthiness
Project suggested that energy-absorbing seats that protect the occupant
from vertical loads could enhance occupant survivability and work to
prevent serious injury, thereby enhancing odds for egress and
preventing many debilitating long-term injuries. The FAA established
dynamic seat testing requirements in amendment 23-36 for airplanes
certificated under part 23. Energy absorbing seats benefit a smaller
portion of accident occupants because accident impacts with larger
vertical components tend to reduce occupant survival odds. Energy
attenuation from vertical forces, both static and dynamic, has been
important to crashworthiness regulations within the past 25 years. Seat
deformation throughout the emergency landing sequence is acceptable if
the load path through attachment, seat, and restraint remains
continuous. Coupling the seat performance to the rest of the airframe
response is important to the enhancement and understanding of occupant
survivability. The FAA believes that allowing designers to consider a
particular airframe's unique deformation in a crash, the designers can
create a safer cabin for the occupants. Using unique airframe
deformations would result in more accurate accident floor impulses and
may allow evaluation of crash impulses in multiple directions; instead
of only two directions considered in current certification.
    Occupant restraints must maintain integrity, stay in place on the
occupant throughout the event, properly distribute loads on the
occupant, and restrain the occupant by mitigating interaction with
other items in the cabin. Restraints originally were comprised of lap
belts. Shoulder harnesses were later required as discussed above. Newer
technology that enhances or supplements the performance of restraints,
like airbags and consideration of items in the cabin that the occupant
might impact, are now being considered for inclusion in designs. The
use of airbags has greatly increased passenger safety in automobiles,
which offer protection in much more severe impacts and in impacts from
multiple directions, and could be a viable option for airplanes as
well.
    Seat retention in airplanes is a factor identified as another basic
building block for crashworthiness. The NTSB reports shows more than a
quarter of otherwise-survivable accidents included instances where the
seats broke free at the attachment to the airplane, resulting in
fatalities or serious injuries. Dynamic seat testing requirements
address the ability of seat assemblies to remain attached to the floor,
even when the floor shifts during impact. Pitching and yawing of the
seat tracks during dynamic seat tests demonstrates the gimbaling and
flexibility of the seat.
    All of the aforementioned safety considerations must work together
to enhance occupant safety and survivability. The FAA believes that
evaluating occupant safety, as a whole system, would allow for a better
understanding of vehicle performance in an emergency landing, enabling
the incorporation of innovative technology. The transportation industry
has made significant progress with energy absorbing seats and restraint
technology. The FAA believes enhanced cabin strength that improves
survivable volume, coupled with better restraint technology and refined
energy absorbing seats, would be key factors in improving expansion of
the survivable accident envelope. These factors and additional
considerations were included in the Small Airplane Crashworthiness
Design Guide.\23\ This guide was prepared for the Advanced General
Aviation Transports Experiments and the National Aerospace and Space
Administration and addresses the concept of designing crashworthiness
into an airplane design as a system.
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    \23\ See www.regulations.gov (Docket #FAA-2015-1621).
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    In order to evaluate an accident from an occupant's perspective,
the emergency landing condition must first be defined, starting with
the conditions external to the aircraft. In most survivable accidents,
the pilot is able to maintain control of the aircraft prior to impact.
Accidents where the airplane impacts the ground out of control are
typically much less survivable. Speed and impact orientation are
significant factors in crash survivability. Therefore, considerations
for impact beyond a controllable impact are beyond the scope of these
proposed regulations. The slowest forward speed that any fixed wing
airplane can fly is its stall speed. This stall speed can vary with
airplane configuration and weight, but represents the most universal
parameter for impact speed and energy attenuation at impact. For this
reason, stall speed is the starting point for consideration of expected
impact conditions.
    Orientation of impact can vary with pitch, yaw, terrain angle, and
angle of flight path and becomes dynamic as the pilot loses control
effectiveness at stall. The result is the airplane impact angle can
result in a combination of horizontal and vertical loads and impulses
that vary widely. Angle of impact, the line of the center of mass with
respect to the angle of the impact surface, can also affect the amount
of energy absorbed or transmitted to the occupant.
    An accident impulse is a dynamic event that rapidly loads and
unloads the structure. Dynamic impacts accurately represent the impact
event, often including load levels far surpassing the static load
requirements. Dynamic testing is also subject to a wide variation of
results due to the unpredictable dynamic responses of varying

construction methods and materials, resulting in complicated modeling
and analysis. This contrasts with static load tests that load the
structure slowly, maintain that load at high levels, are generally
simpler, and often provide adequate demonstration of part strength.
Static analysis is generally more reliable with both testing and
modeling; however, it does not capture the nature of rapid loading.
Some combination of dynamic and static testing allows for the best
understanding of airplane behavior during an accident.
    Compliance with the proposed rule could be shown using conventional
means of compliance like dynamic testing of seats, and static testing
of other components using the prescriptive methods contained in the
current part 23. Alternative compliance methods could include analysis
or modeling supported by testing using an airframe coupled with the
airplane's performance envelope, viewing the entire interaction of
ground, airplane, and occupant, thus using a more complete systemic
approach to achieve improved protection.
    Proposed Sec.  23.600(a) is intended to provide structural
performance that protects the occupant during an emergency landing
while accounting for only static loads and assuming all safety
equipment is in use. The proposed section would capture the safety
intent of the current Sec.  23.561. As noted earlier, static loads are
generally lower than peak dynamic loads; however, they may offer a
more-easily predictable loading condition and are generally of longer
duration such that the structure can fully react to the load. The
landing conditions should consider possible accident sequence variables
at impact, including restraint of items of mass within the cabin,
directions of loading along or about the three axes, and airframe
response with respect to the occupants and effects of airframe
deflection during an emergency landing. Effects of emergency landing on
the airplane should also be considered to include the effect of
airframe damage and how static loads would affect egress and survivable
cabin volume. Items of mass within the cabin and rear mounted engines
have also been traditionally considered using even higher static loads
as an additional factor of safety to ensure that these items of mass
are restrained and would be among the last items to come free in an
accident.
    Proposed Sec.  23.600(b) is intended to provide boundary conditions
for the emergency landing sequence for both static and dynamic load
considerations. The proposed section would capture the safety intent of
the current Sec. Sec.  23.561 and 23.562. The airplane stall speed
limits the maximum forward impact speed. The emergency landing
condition assumes the pilot maintains airplane control at or near final
impact, thereby limiting impact velocity.
    Proposed Sec.  23.600(c) would capture the survivability factors
for the occupant in the cabin during the emergency landing sequence and
would capture the safety intent of current Sec.  23.562. These factors
include proper use and loading of seats and restraints, and the
interaction of the occupants with each other and the cabin interior.
Survivability is determined upon the occupant's interaction with the
interior, seat, and restraints, and bounded by established human injury
criteria.
    Proposed Sec.  23.600(d) would provide the framework for seats and
occupant restraints and would require simplified seat and restraint
requirements for all occupants. This proposed section would capture the
safety intent of current Sec.  23.785.
    Proposed Sec.  23.600(e) would establish requirements for baggage
and cargo compartments and the restraint of contents. The proposed
section would capture the safety intent of current Sec.  23.787.
xvi. Current Subpart C Regulations Relocated to Other Proposed Subparts
    As discussed, the FAA proposes removing current Sec. Sec.  23.561,
23.562, 23.785, and 23.787. Also, this proposal would consolidate the
safety intent of these crashworthiness regulations in proposed Sec.
23.600.
4. Subpart D--Design and Construction
a. General Discussion
    The FAA proposes restructuring current subpart D to retain the
requirements for flight control systems, along with their attachment to
the structure and landing gear, and occupant safety other than
structural requirements. The FAA proposes to align structural
requirements, found in current Sec. Sec.  23.601 through 23.659, to
proposed subpart C. Aspects that directly affected the pilot's
interface with the airplane, such as the throttle shape, would be
relocated to proposed Sec.  23.1500, Flightcrew Interface.
    The FAA also proposes, in those sections where there are
requirements specific to the current commuter category, to use
certification level 4. In those sections where there are current
requirements specific to multiengine jets over 6,000 pounds, the FAA
proposes requirements for certification level 3, high-speed multiengine
airplanes as discussed earlier in this proposal. Refer to appendix 1 of
this preamble for a cross-reference table detailing how the current
regulations are addressed in the proposed part 23 regulations.
    The subpart D organization was more complex than other subparts due
to the relocation and removal of many requirements at the sub-paragraph
level. To reduce confusion, the specific discussion of subpart D
changes is shown in a cross reference table at the end of the specific
discussion section below rather than the Relocation and Removal
paragraphs in other subparts.
b. Specific Discussion of Changes
i. Proposed Sec.  23.700, Flight Controls Systems
    Proposed Sec.  23.700 would require an applicant to design airplane
flight control systems to prevent major, hazardous, and catastrophic
hazards. Proposed Sec.  23.700 would require an applicant to design
trim systems to prevent inadvertent, incorrect, or abrupt trim
operation. In addition, proposed Sec.  23.700 would require an
applicant to design trim systems to provide a means to indicate--
     The direction of trim control movement relative to
airplane motion;
     The trim position with respect to the trim range;
     The neutral position for lateral and directional trim; and
     For all airplanes except simple airplanes, the range for
takeoff for all applicant requested center of gravity ranges and
configurations.
    Proposed Sec.  23.700 would also require an applicant to design
trim systems to provide control for continued safe flight and landing
when any one connecting or transmitting element in the primary flight
control system failed, except for simple airplanes. Additionally,
proposed Sec.  23.700 would require an applicant to design trim systems
to limit the range of travel to allow safe flight and landing, if an
adjustable stabilizer is used.
    Furthermore, proposed Sec.  23.700 would require the system for an
airplane equipped with an artificial stall barrier system to prevent
uncommanded control or thrust action and provide for a preflight check.
The FAA also proposes requiring an applicant seeking certification of a
certification level 3 high-speed or certification level 4 airplane to
install a takeoff warning system on the airplane, unless the applicant
demonstrates that the airplane, for each configuration, could takeoff
at the limits of its trim and flap ranges.
    Proposed Sec.  23.700(b)(3) would also allow an exception for
simple airplanes

from the requirement to provide control for continued safe flight and
landing when any one connecting or transmitting element in the primary
control system fails. This would provide a level of safety equivalent
to that specified in EASA's CS-VLA. Last, proposed Sec.  23.700(d)
would maintain the level of safety in the current requirements for a
takeoff warning system.
    Proposed Sec.  23.700 would capture the safety intent of current
Sec. Sec.  23.677, Trim systems, paragraphs (a), (b), and (d); 23.689,
Cable systems, paragraphs (a) and (f); 23.691, Artificial stall barrier
system, paragraphs (a), (b), (d), (e) and (f); 23.697, Wing flap
controls, paragraphs (a); and 23.703, Takeoff warning system,
paragraphs (a) and (b). This proposed section would apply to the
function, usability, and hazard levels of all mechanical, electrical,
or electronic control systems. The certification levels proposed in
this NPRM would be incorporated into the mechanical, electrical, or
electronic control systems to maintain the differences in airplanes
certificated under part 23 (i.e., weight and powerplant.)
ii. Proposed Sec.  23.705, Landing Gear Systems
    Proposed Sec.  23.705 would require an airplane's landing gear and
retracting mechanism be able to withstand operational and flight loads.
Proposed Sec.  23.705 would require an airplane with retractable
landing gear to have a positive means to keep the landing gear extended
and a secondary means for extending the landing gear that could not be
extended using the primary means. Proposed Sec.  23.705 would also
require a means to inform the pilot that each landing gear is secured
in the extended and retracted positions. Additionally, proposed Sec.
23.705 would require an airplane, except for airplanes intended for
operation on water, with retractable landing gear to also have a
warning to the pilot if the thrust and configuration is selected for
landing and yet the landing gear is not fully extended and locked.
    Furthermore, if the landing gear bayis used as the location for
equipment other than the landing gear, proposed Sec.  23.705 would
require that equipment be designed and installed to avoid damage from
tire burst and from items that may enter the landing gear bay. Proposed
Sec.  23.705 would also require the design of each landing gear wheel,
tire, and ski account for critical loads and would require a reliable
means of stopping the airplane with kinetic energy absorption within
the airplane's design specifications for landing. For certification
level 3 high-speed multiengine and certification level 4 multiengine
airplanes, proposed Sec.  23.705 would require the braking system to
provide kinetic energy absorption within the design of the airplane
specifications for rejected takeoff as the current rules do for
multiengine jets over 6,000 pounds and commuter category airplanes.
    Proposed Sec.  23.705 would capture the safety intent of current
Sec. Sec.  23.729, Landing gear extension and retraction system,
paragraphs (a), (b), (c), and (e); 23.731, Wheels; 23.733, Tires,
paragraph (a); 23.735, Brakes, paragraphs (a), (b), and (e); 23.737,
Skis. The FAA proposes to combine the fixed and retractable landing
gear systems into the proposed section, which would apply to the
function, usability, and hazard levels of all mechanical, electrical,
or electronic landing gear systems.
iii. Proposed Sec.  23.710, Buoyancy for Seaplanes and Amphibians
    Proposed Sec.  23.710 would require airplanes intended for
operations on water to provide buoyancy of 80 percent in excess of the
buoyancy required to support the maximum weight of the airplane in
fresh water. Proposed Sec.  23.710 would also require airplanes
intended for operations on water to have sufficient watertight
compartments so the airplane will stay afloat at rest in calm water
without capsizing if any two compartments of any main float or hull are
flooded.
    Proposed Sec.  23.710 would capture the safety intent of current
Sec. Sec.  23.751(a), Main float buoyancy; 23.755, Hulls; and 23.757,
Auxiliary floats. The FAA proposes combining the floats or hulls
landing gear systems into the proposed section and having it apply to
the function, usability, and hazard levels of hulls and floats. The
existing rule requires at least four watertight compartments of
approximately equal volume, which the FAA proposes to remove because
they are specific design requirements and are addressed in the proposed
performance-based requirements.
    To encourage the installation of buoyancy systems with new safety
enhancing technology and streamlining the certification process, the
FAA proposes removing most of the current prescriptive requirements and
the detailed means of compliance for these requirements from the
current part 23 and replacing them with performance-based regulations.
The FAA expects the current means of compliance would continue to be
used for the traditional airplane designs under part 23.
iv. Sec.  23.750, Means of Egress and Emergency Exits
    Proposed Sec.  23.750 would require the airplane cabin exit be
designed to provide for evacuation of the airplane within 90 seconds in
conditions likely to occur, excluding ditching, following an emergency
landing. For ditching, proposed Sec.  23.750 would require the cabin
exit for all certification levels 3 and 4 multiengine airplanes be
designed to allow evacuation in 90 seconds. Proposed Sec.  23.750 would
require each exit to have a simple and obvious means, marked inside and
outside the airplane, to be opened from both inside and outside the
airplane, when the internal locking mechanism is in the locked
position.
    Proposed Sec.  23.750 would also require airplane evacuation paths
to protect occupants from serious injury from the propulsion system,
and require that doors, canopies, and exits be protected from opening
inadvertently in flight. Proposed Sec.  23.750 would preclude each exit
from being obstructed by a seat or seat back, unless the seat or seat
back could be easily moved in one action to clear the exit. Proposed
Sec.  23.750 would also require airplanes certified for aerobatics to
have a means to exit the airplane in flight.
    Proposed Sec.  23.750 would capture the safety intent of current
Sec. Sec.  23.783, Doors, paragraphs (a), (b), (c), and (d); 23.791,
23.803, Emergency evacuation, paragraph (a); 23.805, Flightcrew
emergency exits; 23.807, Emergency exits except paragraphs (a)(3),
(b)(1), (c), (d)(1) and (d)(4); 23.811, Emergency exit marking; 23.812,
Emergency lighting; 23.813, Emergency exit access, paragraph (a); and
23.815, Width of aisle; and CS-VLA-783, Exits. This proposed rule would
incorporate the requirements for all door and emergency exits and
remove specified design solutions and means of compliances.
    To encourage the installation of egress and emergency exits with
new safety enhancing technology and streamline the certification
process, the FAA proposes removing most of the current prescriptive
requirements and the detailed means of compliance for these
requirements from the current part 23. The FAA expects that the current
prescriptive means of compliance would continue to be used for
traditional part 23 airplane designs.
    The FAA would continue to accept an airplane designed to meet these
prescriptive design constraints as means of compliance to meet the
proposed performance standard. However, if an airplane did not meet the
prescriptive design constraints, the applicant could

propose its own means of compliance to show compliance with the
proposed performance standard. Historically, the FAA has accepted an
emergency evacuation demonstration in less than 90 seconds as an ELOS
for airplanes that did not meet the prescriptive design requirements in
the current part 23 regulations. AC 20-118A, Emergency Evacuation
Demonstration, contains an acceptable means of compliance for the 90-
second requirement for emergency evacuation.
v. Proposed Sec.  23.755, Occupant Physical Environment
    Proposed Sec.  23.755 would require an applicant to design the
airplane to allow clear communication between the flightcrew and
passengers and provide a clear, sufficiently undistorted external view
to enable the flightcrew to perform any maneuvers within the operating
limitations of the airplane. Proposed Sec.  23.755 would also require
an applicant to design the airplane to protect the pilot from serious
injury due to high energy rotating failures in systems and equipment,
and protect the occupants from serious injury due to damage to
windshields, windows, and canopies.
    Additionally, proposed Sec.  23.755 would require, for
certification level 4 airplanes, each windshield and its supporting
structure directly in front of the pilot to withstand the impact
equivalent of a two-pound bird at maximum approach flap airspeed and
allow for continued safe flight and landing after the loss of vision
through any one panel.
    Furthermore, proposed Sec.  23.755 would require any installed
oxygen system to include a means to determine whether oxygen is being
delivered and a means for the flightcrew to turn on and shut off the
oxygen supply, and the ability for the flightcrew to determine the
quantity of oxygen available. Proposed Sec.  23.755 would also require
any installed pressurization system to include a pressurization system
test and a warning if an unsafe condition exists.
    Proposed Sec.  23.755 would capture the safety intent of current
Sec. Sec.  23.771, Pilot compartment, paragraphs (b) and (c); 23.775,
Windshields and windows, paragraphs (a), (b), (c), (d), and (h);
23.831, Ventilation; 23.841, Pressurized cabins, paragraphs (a),
(b)(6), (c) and (d); 23.843, Pressurization tests; 23.1441, Oxygen
equipment and supply, paragraphs (c), (d) and (e); 23.1443, minimum
mass flow of supplemental oxygen, paragraphs (a), (b), and (c);
23.1445; Oxygen distribution system; 23.1447, Equipment standards for
oxygen dispensing units, paragraphs (a) through (d) and (f); 23.1449,
means of determining use of oxygen; and 23.1461, Equipment containing
high energy rotors. Current part 23 regulations contain prescriptive
language and means of compliance for the occupant physical environment
requirements. The FAA proposes to remove the specific requirements to
allow an applicant to specify the means of compliance for the physical
needs of the occupants including temperature, ventilation,
pressurization, supplemental oxygen, etc. For example, current Sec.
23.831(a) requires carbon monoxide not exceeding one part in 20,000
parts of air. The FAA proposes revising this by requiring breathable
atmosphere without hazardous concentrations of gases and vapors.
vi. Proposed Sec.  23.800, Fire Protection Outside Designated Fire
Zones
    Proposed Sec.  23.800 would require that insulation on electrical
wire and electrical cable outside designated fire zones be self-
extinguishing. Proposed Sec.  23.800 would require airplane cockpit and
cabin materials in certification levels 1, 2, and 3 be flame-resistant.
Proposed Sec.  23.800 would require airplane cockpit and cabin
materials in certification level 4 airplanes be self-extinguishing.
Proposed Sec.  23.800 would also require that airplane materials in the
baggage and cargo compartments, which are inaccessible in flight and
outside designated fire zones, be self-extinguishing. Proposed Sec.
23.800 would require that any electrical cable installation that would
overheat in the event of circuit overload or fault be flame resistant.
Additionally, proposed Sec.  23.800 would preclude thermal acoustic
materials outside designated fire zones from being a flame propagation
hazard. Proposed Sec.  23.800 would also require sources of heat that
are capable of igniting adjacent objects outside designated fire zones
to be shielded and insulated to prevent such ignition.
    Proposed Sec.  23.800 would require airplane baggage and cargo
compartments, outside designated fire zones, to be located where a fire
would be visible to the pilots, or equipped with a fire detection
system and warning system, and be accessible for the manual
extinguishing of a fire, have a built-in fire extinguishing system, or
be constructed and sealed to contain any fire within the compartment.
    Proposed Sec.  23.800 would require a means to extinguish any fire
in the cabin, outside designated fire zones, such that the pilot, while
seated, could easily access the fire extinguishing means, and for
certification levels 3 and 4 airplanes, passengers would have a fire
extinguishing means available within the passenger compartment. Where
flammable fluids or vapors might escape by leakage of a fluid system,
proposed Sec.  23.800 would require each area, outside designated fire
zones, be defined and have a means to make fluid and vapor ignition,
and the resultant hazard, if ignition occurs, improbable. Additionally,
proposed Sec.  23.800 would also require combustion heater
installations outside designated fire zones be protected from
uncontained fire.
    Proposed Sec.  23.800 would capture the safety intent of current
Sec. Sec.  23.851, Fire extinguishers, paragraphs (a) and (b); 23.853,
Passenger and crew compartment interiors, Paragraphs (a), (d)(3)(i),
(d)(3)(iii) and (d)(3)(iv), (e), and (f); 23.855, Cargo and baggage
compartment fire protection; 23.856, Thermal/acoustic insulation
materials; 23.859, Combustion heater fire protection, paragraph (a);
23.863, Flammable fluid fire protection, paragraphs (a) and (d);
23.1359, Electrical system fire protection, paragraph (c); 23.1365,
Electric cables and equipment, paragraph (b); 23.1383, Taxi and landing
lights, paragraph (d); 23.1385, Position light system installation,
paragraph (d). It would also capture the safety intent of CS-VLA-853,
Compartment interiors. Proposed Sec.  23.800 would incorporate the
requirements for flammability of all subpart D and F systems and
equipment outside designated fire zones needed for continued safe
flight and landing and remove specified design solutions and means of
compliances.
vii. Proposed Sec.  23.805, Fire Protection in Designated Fire Zones
    Proposed Sec.  23.805 would require flight controls, engine mounts,
and other flight structures within or adjacent to designated fire zones
be capable of withstanding the effects of a fire. Proposed Sec.  23.805
would require engines inside designated fire zones to remain attached
to the airplane in the event of a fire or electrical arcing. Proposed
Sec.  23.805 would also require terminals, equipment, and electrical
cables, inside designated fire zones, used during emergency procedures,
be fire-resistant.
    Proposed Sec.  23.805 would capture the safety intent of current
Sec.  23.865, Fire protection of flight controls, engine mounts, and
other flight structure and Sec.  23.1359(b), Electrical system fire
protection. The intent of proposed Sec.  23.805 is to protect flight
controls, engine mounts, and other flight structure as well as
electrical cables,

terminals and equipment from the effects of fire in designated fire
zones.
viii. Proposed Sec.  23.810, Lightning Protection of Structure
    Proposed Sec.  23.810 would preclude primary structure failure
caused by exposure to the direct effects of lightning, that could
prevent continued safe flight and landing for airplanes approved for
IFR. Proposed Sec.  23.810 would require airplanes approved only for
VFR to achieve lightning protection by following FAA accepted design
practices found in FAA issued advisory circulars and in FAA accepted
consensus standards.
    Proposed Sec.  23.810 would capture the safety intent of the
current Sec.  23.867(a) and (c), Electrical bonding and protection
against lightning and static electricity. The FAA proposes adopting the
structure requirements in part 23, amendment 23-7 (34 FR 13078, August
13, 1969), to limit the rule to protection of primary structure from
direct effects of lightning.
ix. Reorganization of Subpart D
    The FAA proposes relocating the underlying safety. intent of
various subpart D sections with proposed sections in subparts B, C, F,
and G. The following table shows where the FAA proposes moving the
current subpart D sections in part 23.

----------------------------------------------------------------------------------------------------------------
           Current section                      Title               Proposed section          Proposed title
----------------------------------------------------------------------------------------------------------------
23.601...............................  General................  23.500.................  Structural design.
23.603...............................  Materials and            23.500.................  Structural design.
                                        workmanship.
23.605...............................  Fabrication methods....  23.510.................  Materials and
                                                                                processes.
23.607...............................  Fasteners..............  23.505.................  Protection of
                                                                                structure.
23.609...............................  Protection of Structure  23.505.................  Protection of
                                                                                structure.
23.611...............................  Accessibility..........  23.505.................  Protection of
                                                                                structure.
23.613...............................  Material strength        23.510.................  Materials and
                                        properties and design                             processes.
                                        values.
23.619...............................  Special factors........  23.515.................  Special factors of
                                                                                safety.
23.621...............................  Casting factors........  23.515.................  Special factors of
                                                                                safety.
23.623...............................  Bearing factors........  23.515.................  Special factors of
                                                                                safety.
23.625...............................  Fitting factors........  23.515.................  Special factors of
                                                                                safety.
23.627...............................  Fatigue strength.......  23.405.................  Structural durability.
23.629...............................  Flutter................  23.410.................  Aeroelasticity.
23.641...............................  Proof of strength......  Means of Compliance....
23.651...............................  Proof of strength......  Means of Compliance....
23.655...............................  Installation...........  Means of Compliance....
23.657...............................  Hinges.................  23.515.................  Special factors of
                                                                                safety.
23.659...............................  Mass balance...........  23.315.................  Flight load conditions.
23.671...............................  Control Surfaces--
                                        General.
(a)..................................  .......................  23.500.................  Structural design.
(b)..................................  .......................  23.1305................  Function and
                                                                                installation.
23.672...............................  Stability augmentation   23.1305................  Function and
                                        and automatic and                                 installation.
                                        power-operated systems.
23.673...............................  Primary flight controls  23.1305................  Function and
                                                                                installation.
23.675...............................  Stops..................  23.1305................  Function and
                                                                                installation.
23.677...............................  Trim systems...........
(a)..................................  .......................  23.700.................  Flight control systems.
(b)..................................  .......................  23.700.................  Flight control systems.
(c)..................................  .......................  23.410.................  Aeroelasticity.
(d)..................................  .......................  23.700.................  Flight control systems.
23.679...............................  Control system locks...  23.1305................  Function and
                                                                                installation.
23.681(a)............................  Limit load static tests  23.325(b)..............  Component loading
                                                                                conditions.
23.681(b)............................  Limit load static tests  23.515.................  Special factors of
                                                                                safety.
23.683...............................  Operation tests........  23.500(d)..............  Structural design.
23.685(a), (b), (c)..................  Control system details.  23.500(d)..............  Structural design.
23.685(d)............................  Control system details.  23.1305................  Function and
                                                                                installation.
23.687...............................  Spring devices.........  23.410 and 23.500......  Aeroelasticity and
                                                                                Structural design.
23.689...............................  Cable systems..........  .......................  Component loading
                                                                                conditions, Structural
                                                                                design, and Equipment
                                                                                Systems and
                                                                                Installations.
(a)..................................  .......................  23.700.................  Flight control systems.
(b)..................................  .......................  23.325(b), 23.500(d)...  Component loading
                                                                                conditions, Structural
                                                                                design.
(c)..................................  .......................  23.325(b), 23.500(d)...  Component loading
                                                                                conditions, Structural
                                                                                design.
(d)..................................  .......................  23.325(b), 23.500(d)...  Component loading
                                                                                conditions, Structural
                                                                                design.
(e)..................................  .......................  23.325(b), 23.500(d)...  Component loading
                                                                                conditions, Structural
                                                                                design.
(f)..................................  .......................  23.700.................  Flight control systems.
23.691...............................  Artificial stall
                                        barrier system.
(a)..................................  .......................  23.700.................  Flight control systems.
(b)..................................  .......................  23.700.................  Flight control systems.
(c)..................................  .......................  23.1305................  Function and
                                                                                installation.
(d)..................................  .......................  23.700.................  Flight control systems.
(e)..................................  .......................  23.700.................  Flight control systems.
(f)..................................  .......................  23.700.................  Flight control systems.
(g)..................................  .......................  23.1315................  Equipment, systems and
                                                                                Installations.
23.693...............................  Joints.................  23.515.................  Special factors of
                                                                                safety.

23.697...............................  Wing flap controls.....
(a)..................................  .......................  23.700.................  Flight control systems.
(b) and (c)..........................  .......................  23.200.................  Controllability.
23.699...............................  Wing flap position       23.1500................  Flightcrew interface.
                                        indicator.
23.701...............................  Flap interconnection...  Means of Compliance....
23.703...............................  Takeoff warning system.
(a)..................................  .......................  23.700.................  Flight control systems.
(b)..................................  .......................  23.700.................  Flight control systems.
(c)..................................  .......................  Definition.............
23.721...............................  General................  23.910.................  Powerplant installation
                                                                                hazard assessment.
23.723...............................  Shock absorption tests.  Means of Compliance....
23.725...............................  Limit drop tests.......  Means of Compliance....
23.726...............................  Ground load dynamic      Means of Compliance....
                                        tests.
23.727...............................  Reserve energy           Means of Compliance....
                                        absorption drop tests.
23.729...............................  Landing gear extension
                                        and retraction system.
(a)..................................  .......................  23.705.................  Landing gear systems.
(b)..................................  .......................  23.705.................  Landing gear systems.
(c)..................................  .......................  23.705.................  Landing gear systems.
(d)..................................  .......................  Means of Compliance....
(e)..................................  .......................  23.705.................  Landing gear systems.
(f)..................................  .......................  23.1315................  Equipment, systems and
                                                                                installation.
(g)..................................  .......................  Means of Compliance....
23.731...............................  Wheels.................  23.705.................  Landing gear systems.
23.733...............................  Tires..................
(a)..................................  .......................  23.705.................  Landing gear systems.
(b)..................................  .......................  Means of Compliance....
(c)..................................  .......................  Means of Compliance....
23.735...............................  Brakes.................  23.705.................
(a)..................................  .......................  23.705.................  Landing gear systems.
(1)..................................  .......................  Means of Compliance....
(2)..................................  .......................  Means of Compliance....
(b)..................................  .......................  23.705.................  Landing gear systems.
(c)..................................  .......................  Means of Compliance....
(d)..................................  .......................  23.1315................  Equipment, systems and
                                                                                installation.
(e)..................................  .......................  23.705.................  Landing gear systems.
(1)..................................  .......................  Means of Compliance....
(2)..................................  .......................  Means of Compliance....
23.737...............................  Skis...................  23.705.................  Landing gear systems.
23.745...............................  Nose/Tail wheel          23.1500................  Flightcrew interface.
                                        steering.
23.751...............................  Main float buoyancy....
(a)..................................  .......................  710....................  Buoyancy for seaplanes
                                                                                and amphibians.
(b)..................................  .......................  Means of Compliance....
23.753...............................  Main float design......  23.320.................  Ground and water load
                                                                                conditions.
23.755...............................  Hulls..................  23.710.................  Buoyancy for seaplanes
                                                                                and amphibians.
23.757...............................  Auxiliary floats.......  23.710.................  Buoyancy for seaplanes
                                                                                and amphibians.
23.771...............................  Pilot compartment......
(a)..................................  .......................  23.1500................  Flightcrew interface.
(b)..................................  .......................  23.755.................  Occupant physical
                                                                                environment.
(c ).................................  .......................  23.755.................  Occupant physical
                                                                                environment.
23.773...............................  Pilot compartment view.
(a)..................................  .......................  23.1500................  Flightcrew interface.
(b)..................................  .......................  23.755.................  Occupant physical
                                                                                environment.
23.775...............................  Windshields and windows
(a), (b), (c), (d)...................  .......................  23.755.................  Occupant physical
                                                                                environment.
(e)..................................  .......................  Means of Compliance....
(f)..................................  .......................  23.1405................  Flight in icing
                                                                                conditions.
(g)..................................  .......................  Means of Compliance....
(h)..................................  .......................  23.755.................  Occupant physical
                                                                                environment.
23.777...............................  Cockpit controls.......  23.1500................  Flightcrew interface.
23.779...............................  Motion and effect of     23.1500................  Flightcrew interface.
                                        cockpit controls.
23.781...............................  Cockpit control knob     23.1500................  Flightcrew interface.
                                        shape.
23.783...............................  Doors..................
(a), (b), (c), (d)...................  .......................  23.750.................  Means of egress and
                                                                                emergency exits.
(e), (f), (g)........................  .......................  Means of Compliance....
23.785...............................  Seats, berths, litters,  23.600 and 23.515......  Special factors of
                                        safety belts, and                                 safety, Emergency
                                        shoulder harnesses.                               landing conditions.
23.787...............................  Baggage and cargo        23.600(e)..............  Emergency landing
                                        compartments.                                     conditions.
23.791...............................  Passenger information    23.755.................  Occupant physical
                                        signs.                                            environment.
23.803...............................  Emergency evacuation...

(a)..................................  .......................  23.750.................  Means of egress and
                                                                                emergency exits.
(b)..................................  .......................  Means of Compliance....
23.805...............................  Flightcrew emergency     23.750.................  Means of egress and
                                        exits.                                            emergency exits.
23.807...............................  Emergency exits........
(a)(3 ), (b)(1), (c), (d)(1), (d)(4).  .......................  Means of Compliance....
Balance of 23.807....................  .......................  23.750.................  Means of egress and
                                                                                emergency exits.
23.811...............................  Emergency exit marking.  23.750.................  Means of egress and
                                                                                emergency exits.
23.812...............................  Emergency lighting.....  23.750.................  Means of egress and
                                                                                emergency exits.
23.813...............................  Emergency exit access..
(a)..................................  .......................  23.750.................  Means of egress and
                                                                                emergency exits.
(b)..................................  .......................  Means of Compliance....
CS-VLA 853...........................  .......................  23.750.................  Means of egress and
                                                                                emergency exits.
23.815...............................  Width of aisle.........  23.750.................  Means of egress and
                                                                                emergency exits.
23.831...............................  Ventilation............  23.755.................  Occupant physical