requirement. Moreover, Sec.  23.2305(c)(1) does not increase the burden
on traditional designs; provides flexibility to allow new designs to be
certified because it applies to all landing gear actuated by a system,
not just retractable landing gear; and assists in harmonization.
    The FAA adopts the language of CS 23.2325(d)(4) as Sec.
23.2305(c)(2), with one minor change. The FAA is using the phrase ``a
hazard'' instead of ``hazardous'' to avoid confusion with former Sec.
23.1309's use of the phrase ``hazardous failure condition.'' The
language of CS 23.2325(d)(4) better captures the safety intent of
former Sec.  23.729(c), which did not require a secondary means for
landing gear that could be extended manually, and is less prescriptive
because it only requires an alternative means to bring the landing gear
to the landing position if a non-deployed position would be a hazard.
Additionally, moving the location of this requirement has no technical
impact and harmonizes with CS 23.2325.
    The FAA does not adopt proposed Sec.  23.705(a)(2)(iii) or the
language from CS 23.2325(d)(2) and (d)(3) because the FAA considers
both proposals to be adequately addressed by proposed Sec.  23.1500(b)
(now Sec.  23.2600(b)). Section 23.2600(b) requires the applicant to
install flight, navigation, surveillance, and powerplant controls and
displays so qualified flightcrew can monitor and perform defined tasks
associated with the intended functions of systems and equipment. The
systems and equipment design must minimize flightcrew errors which
could create additional hazards. Section 23.2600(b) incorporates the
safety intent of previous requirements for landing gear indications and
effectively requires the pilot to be informed of the landing gear
position (secured in extended or retracted position) should the pilot
need that information.
    Textron recommended the FAA remove the requirement for a secondary
means of extending the landing gear in proposed Sec.  23.705 and rely
instead on the requirements of proposed Sec.  23.1315.
    The FAA disagrees as Textron's recommendation does not capture the
intent of the former regulation, which was a specific requirement for a
secondary means of deploying landing gear. Furthermore, this
requirement in proposed Sec.  23.705 was not covered by the general
systems failure requirements of proposed Sec.  23.1315.
    Several commenters recommended deleting proposed Sec.
23.705(a)(2)(iv), in part, because it was too prescriptive. One
commenter recommended rewriting the rule as a performance[hyphen]based
regulation to encourage alternate--and perhaps better--means of
detecting wrong configurations for landing.
    The FAA agrees that proposed Sec.  23.705(a)(2)(iv) is too
prescriptive, and finds it is adequately addressed by the requirements
of new Sec.  23.2605(c), which requires information concerning an
unsafe system operating condition must be provided in a timely manner
to the crewmember responsible for taking corrective action.
Accordingly, the FAA withdraws proposed Sec.  23.705(a)(2)(iv).
    Textron recommended the FAA add the word ``essential'' before
``equipment'' in proposed Sec.  23.705(a)(3),\37\ asserting that non-
essential equipment is not important to protect in the landing gear
bay.
---------------------------------------------------------------------------

    \37\ Textron referenced ``the 2nd line of the 2nd paragraph,''
but the FAA infers they intended to reference proposed Sec.
23.705(a)(3) because this is the provision that would require
protection of equipment.
---------------------------------------------------------------------------

    The FAA disagrees with Textron's recommendation as it is possible
that failures of non-essential equipment like a fuel line for a
combustion heater may result in hazards more severe than the loss of
the non-essential function. Therefore, the FAA is not adopting this
change in the final rule.
    Textron recommended rewording proposed Sec. Sec.  23.705(c) and (d)
to limit their applicability to airplanes with wheels, asserting these
paragraphs required airplanes without wheels to have brakes.
Alternatively, Textron suggested moving the requirement to proposed
Sec.  23.1300(a) (now Sec.  23.2500(a)) because an airplane with wheels
will need a braking system to meet proposed Sec.  23.1300(a), making
Sec.  23.705(c) redundant. Other commenters recommended the FAA replace
proposed Sec.  23.705(c) and (d) with the CS 23.2325(c), which
addresses kinetic energy absorption.
    The FAA concurs with the recommendation to replace proposed Sec.
23.705(c) and (d) with CS 23.2325(c). The FAA notes CS 23.2325(c) has
the same meaning as proposed Sec.  23.705(c) and (d), but harmonizes
with EASA's NPA 2016-05. The FAA has determined the removal of the
phrase ``within the airplane's design specifications for landing'' and
replacement with ``sufficient . . . to account for landing'' has no
technical impact. The FAA adopts the change as Sec.  23.2305(b).
    The FAA disagrees with Textron's recommendation to reword Sec.
23.705(c) and (d) to limit their applicability to airplanes with
wheels. The FAA notes proposed paragraphs (c) and (d) would not require
brakes. While the FAA has considered Textron's alternative
recommendation, the specific energy absorption requirement of proposed
Sec.  23.705(c) is not adequately addressed by the general system
performance requirements of proposed Sec.  23.1300(a). Therefore, the
FAA is not adopting this change in the final rule.
    Textron suggested the FAA should harmonize its proposed regulations
on this topic with CS 23.600 by removing language related to brakes as
a subset of meeting the requirements of proposed Sec.  23.1300(a).
    The FAA agrees with harmonizing with EASA wherever possible.
However, specifically requiring a reliable means of stopping the
airplane is not excessively prescriptive and provides clarity to the
regulation. Furthermore, Textron's suggested text would not harmonize
with CS 23.2325.
    EASA recommended eliminating the reference to level 3 and 4
airplanes in proposed Sec.  23.705(d), and replacing it with a
reference to airplanes ``required to demonstrate aborted take-off
capacity,'' which links the requirement to takeoff performance.
Similarly, all of the comments on this section recommended making
proposed Sec.  23.705(d) applicable to the same airplanes covered by
proposed Sec.  23.115(c)(1) (now Sec.  23.2115(c)(1)).\38\ Textron also
suggested directly referencing proposed Sec.  23.115 to prevent the
link between the two

requirements from being inadvertently broken.
---------------------------------------------------------------------------

    \38\ Proposed Sec.  23.115(c)(1) would have applied to ``levels
1, 2, and 3 high-speed multiengine airplanes, multiengine airplanes
with a maximum takeoff weight greater than 12,500 pounds and level 4
multiengine airplanes.''
---------------------------------------------------------------------------

    The FAA agrees with the recommendation to make Sec.  23.2305(b)
applicable to the same airplanes as Sec.  23.2115(c)(1) for several
reasons. First, in order to comply with Sec.  23.2115(c)(1), applicants
must design airplanes with a means to decelerate the airplane after a
rejected takeoff, regardless of the requirements in Sec.  23.2305(b),
so adopting the recommended change would not increase the burden on
applicants. Second, making the applicability of Sec.  23.2305(b)
different from Sec.  23.2115(c)(1) could cause confusion, especially
because the proposed applicability would have included airplanes
excluded from Sec.  23.2115(c)(1). In former Sec. Sec.  23.55 and
23.735(e), the FAA applied the requirement to determine the distance
for an aborted takeoff at critical speed to the same airplanes required
to provide kinetic energy absorption in the brakes for a rejected
takeoff, and there is no reason to discontinue this practice.
Additionally, adopting this recommendation harmonizes the FAA
requirement with CS 23.2325(c).
c. Buoyancy for Seaplanes and Amphibians (Proposed Sec.  23.710/Now
Sec.  23.2310)
    In the NPRM, proposed Sec.  23.710 (now Sec.  23.2310) would have
required 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 have
also required 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.
    The FAA noted in the NPRM that it was proposing to remove the
requirement that each main float must contain at least four watertight
compartments of approximately equal volume because it was a specific
design requirement that would be addressed by the proposed performance-
based standard.
    All of the comments on this section noted a problem with the
prescriptive design specificity of proposed Sec.  23.710(b); in
particular, the requirement to have watertight compartments. The
commenters noted an erroneous assumption that all airplanes intended
for operations on water would have watertight compartments. The
commenters noted that manufacturers could employ a different solution--
such as foam-filled floats--eliminating the need for compartments, and
still meet the buoyancy intent. BendixKing commented that the buoyancy
requirement needs to be ``more generic to address the core safety
intent, which is adequate floatation in the event of a failure.'' The
Associations and Textron offered alternative regulatory language that
would remove the requirement to have watertight compartments and
provide a general performance-based standard for demonstrating
buoyancy.
    The FAA agrees that proposed Sec.  23.710(b) is excessively
prescriptive. The FAA recognizes there are other ways to meet the
safety goal of protecting the airplane from capsizing. Therefore, the
FAA revises proposed Sec.  23.710(b) to establish a more performance-
based standard for demonstrating buoyancy.
    ICON noted that hull type and float seaplanes were treated
differently in former part 23, and recommended that they be treated
differently in the new part 23 as well, because they deal with a loss
of buoyancy in different ways. In particular, ICON noted differences in
the rate of capsizing, the ability to detect an intrusion of water, and
the pilot's ability to remove the water while operating the airplane.
ICON asked the FAA to eliminate the separate compartment requirements
for hull[hyphen]type seaplanes.
    The FAA agrees that, as proposed, the combination of hulls and
floats into one regulation would have imposed a requirement on hulls
that is more stringent than the requirements in former part 23. The FAA
revises the proposed language to remove the prescriptive requirement
for watertight compartments. As such, Sec.  23.2310 contains a more
general standard for buoyancy that is appropriate for both floats and
hulls.
d. Means of Egress and Emergency Exits (Proposed Sec.  23.750/Now Sec.
23.2315)
    In the NPRM, proposed Sec.  23.750 (now Sec.  23.2315) would have
required--
     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 have required the cabin exit for
all certification levels 3 and 4 multiengine airplanes be designed to
allow evacuation in 90 seconds;
     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; and
     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 have precluded 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 have also required airplanes certified for aerobatics to have a
means to exit the airplane in flight.
    The Associations, BendixKing, Textron, and EASA recommended the FAA
remove the 90-second evacuation requirement in proposed Sec.  23.750(a)
and replace it with less prescriptive language. EASA stated that the
90-second evacuation time was not contained in the former part 23
regulations and would not be reasonable for all airplanes. EASA stated
that leaving the acceptable design solutions to an acceptable means of
compliance would be better. As alternatives to the proposed language,
BendixKing suggested a requirement for ``adequate and timely''
evacuation, Textron suggested a requirement for ``rapid'' evacuation,
and the Associations suggested a requirement for ``rapid and safe''
evacuation.
    The FAA agrees and removes the airplane 90-second evacuation
requirement because specifying the time limit in the regulation is
unnecessarily prescriptive. The FAA replaces the evacuation requirement
with the requirement to ``facilitate rapid and safe evacuation of the
airplane in conditions likely to occur following an emergency landing,
excluding ditching for level 1, level 2, and single-engine level 3
airplanes.'' This harmonizes more closely with EASA's proposed CS
23.2335.
    The Associations specifically proposed revisions to the regulatory
text, which appeared to align with EASA's proposed regulation. In
accordance with their recommendation, the FAA revises the beginning of
proposed Sec.  23.750(a) to move a portion of its content into Sec.
23.2315(a)(1). Section 23.2315(a) is revised to read: ``With the cabin
configured for take-off or landing, the airplane is designed to,''
followed by more detailed requirements in the subparagraphs. The FAA
believes this change more clearly preserves the intent of former
regulations. It also harmonizes with EASA's proposed regulation.
    Textron also commented that the FAA should either replace the word
``likely'' in proposed Sec.  23.750(a) or ensure the

``likely conditions'' referred to in paragraph (a) are clearly defined
in the ASTM standards. The FAA intends the term ``likely'' to be
nonprecise or within a mathematical certainty. As explained in the
discussion of proposed Sec.  23.205, the FAA finds the most appropriate
location for defining ``likely conditions'' is in a means of
compliance, because these conditions may vary for different airplanes;
therefore, the FAA retains the word ``likely'' in paragraph (a).
    Textron also noted that proposed Sec.  23.750(a) specifies ``likely
conditions,'' but excludes ditching for all but levels 3 and 4
multiengine airplanes. However, Textron stated that ditching as a
likely condition associated with emergency evacuation had not been
required previously. It recommended the FAA add a requirement to
proposed Sec.  23.750, to require a means on levels 3 and 4 multiengine
airplanes to evacuate the airplane safely following a ditching event.
    The FAA notes the requirement to safely evacuate the airplane
during ditching is already addressed generally in Sec.  23.2315(a)(1).
The methods for meeting this requirement will be in a means of
compliance.
    Textron further commented on using former Sec.  23.807(e) as a
means of compliance to show that occupants have a means available to
safely evacuate the airplane. Textron stated that former Sec.
23.807(e) only prescribes one exit on each side of the airplane to be
above the waterline or alternative methods must be employed.
    The FAA agrees that providing one exit on each side of the airplane
above the waterline is an acceptable means of compliance. While this
may be one means of compliance that is acceptable for traditional
designs, the FAA's goal in this rule is to use means of compliance,
developed by industry or individuals, to allow for non-traditional
designs.
    Transport Canada commented on proposed Sec.  23.750(a), noting that
cabin exit design is just one of several elements that affect
evacuation performance. Transport Canada also noted that the
expectation to meet the evacuation performance with the airplane's
maximum certified occupancy should be made explicit. Transport Canada
suggested a revision to proposed paragraph (a) stating that the
airplane design, including the cabin exit design, must provide for
evacuation of the airplane of the maximum number of occupants within 90
seconds in conditions likely to occur following an emergency landing.
    The FAA agrees that cabin exit design is just one of several
elements that affect evacuation performance and that rapid evacuation
with the airplane's maximum certified occupancy is required, but the
regulation does not have to explicitly include this requirement.
Section 23.2315 addresses generally all the likely conditions that
affect emergency evacuation, which would include an airplane with
maximum certificated occupancy. Therefore, the FAA is not adopting the
language proposed by Transport Canada.
    The Associations recommended the following revisions to proposed
Sec.  23.750(a), which deleted or combined portions of proposed
paragraphs (a), (b), (c), (d) and (f) into a new paragraph (a), and
renumbered paragraph (e) as paragraph (b). Their proposed paragraph
(a)(1) appears to correlate with proposed Sec.  23.750(a). They
proposed a revision to proposed paragraph (a)(1) stating that, with the
cabin configured for take-off or landing, the airplane is designed to
facilitate rapid and safe evacuation of the ``aeroplane'' in conditions
likely to occur following an emergency landing, excluding ditching for
level 1, level 2, and single-engine level 3 airplanes.
    The FAA adopts this language as Sec.  23.2315(a)(1), except for
spelling ``aeroplane'' as ``airplane.'' This is better organized and
more understandable than the proposed language, while still retaining
the intent of former regulations and harmonizes the regulations between
FAA and EASA.
    Textron commented that the phrase ``when the internal locking
mechanism is in the locked and unlocked position'' in proposed Sec.
23.750(b) is not necessary and should be deleted. The FAA agrees and
removes the phrase because this is a detailed design consideration,
which is more appropriately addressed in means of compliance.
    Textron also recommended the FAA add a requirement similar to the
requirement for auxiliary locking devices in former Sec.  23.783(c)(6),
which would provide, in pertinent part, that auxiliary locking devices
that are actuated externally to the airplane may be used but such
devices must be overridden by the normal internal opening means.
Textron's view was that auxiliary locking devices used to secure the
airplane would likely be needed to prevent unauthorized entry into the
airplane when it is left unattended.
    The FAA disagrees with Textron's recommendation as the suggested
text because it is more appropriate for a means of compliance.
    The Associations proposed revisions to proposed Sec.  23.750(a)(2)
that coincidently address Textron's comment on internal locking
mechanisms. They suggested adding language stating that, with the cabin
configured for take-off or landing, the airplane is designed to have
means of egress (openings, exits or emergency exits), that can be
readily located and opened from the inside and outside. The means of
opening must be simple and obvious.
    The FAA adopts this language as Sec.  23.2315(a)(2), except the
proposed marking requirement is retained. This revision captures the
safety intent of the former regulations more clearly and harmonizes
regulations between the FAA and EASA.
    The Associations recommended deleting proposed Sec.  23.750(c). The
FAA agrees because paragraph (a)(1), as revised, already addresses
similar requirements, rendering paragraph (c) redundant.
    Textron commented on proposed Sec.  23.750(d) by recommending the
FAA address obstructions more generally (i.e., not just seat backs),
and offered the language stating that each exit must not be obstructed
unless the obstruction can be easily moved in one action to clear the
exit.
    Transport Canada similarly suggested the requirement should more
generally address that any component of the interior should be
considered as a potential obstruction, and also address temporary
obstructions during flight. Transport Canada proposed a revision to
proposed paragraph (d) stating that each exit must not be obstructed by
any interior component during taxi, take-off or landing. In addition, a
seat or seat back may obstruct an exit if the seat or seat back can
[be] easily moved in one action to clear the exit.
    The FAA considered Transport Canada's proposed wording, but moving
a seat back easily in one motion to reach an emergency exit is more
appropriate as a means of compliance. The FAA agrees with Textron's and
Transport Canada's comments on proposed Sec.  23.750(d) that
obstructions that could potentially block exits should be addressed
more generally and not limited to seat backs, because other items could
block exits and impair evacuation. The FAA revises the regulation
accordingly as Sec.  23.2315(a)(3).
    The Associations proposed a revision to proposed Sec.  23.750(a)(3)
stating that, with the cabin configured for take-off or landing, the
airplane is designed to have easy access to emergency exits when
present.
    The FAA is incorporating this suggestion in Sec.  23.2315(a)(3).
The new language captures the safety intent of the former regulations
more generally

and harmonizes the FAA language with the EASA NPA language.
    The Associations recommended to renumber proposed Sec.  23.750(e)
as proposed Sec.  23.750(b) (now Sec.  23.2315(b)). The FAA agrees and
adopts the proposed renumbering. This relocation will not change the
substantive content of the paragraph, but matches with EASA's numbering
and will lessen confusion.
    The Associations recommended deleting proposed Sec.  23.750(f).
EASA commented that the requirement in proposed Sec.  23.750(f) for
doors, etc. is too design-specific and can be covered by generic
principles covered in Sec.  23.2250 (proposed as Sec.  23.500).
    The FAA understands EASA's comment, but requiring doors, canopies,
and exits to be protected from opening inadvertently in flight is a
general requirement that does not limit possible design solutions.
However, the FAA moves this requirement to Sec.  23.2250(e) to
harmonize the location of the requirement with EASA's rule.
    Upon further review, the FAA is replacing the word ``approved'' in
proposed Sec.  23.750(e) (now Sec.  23.2315(b)) with the word
``certified''. This change does not affect the original intent of
paragraph (e), but harmonizes the language with EASA.
e. Occupant Physical Environment (Proposed Sec.  23.755/Now Sec.
23.2320)
    In the NPRM, proposed Sec.  23.755 (now Sec.  23.2320) would have
required 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 have also required 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 have required, for 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 have required 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 have also
required any installed pressurization system to include a
pressurization system test and a warning if an unsafe condition exists.
    EASA commented the requirement in proposed Sec.  23.755(a)(2) for
the airplane design to provide a clear, sufficiently undistorted
external view should be covered in the ``crew interface'' paragraph.
    The FAA agrees with EASA that the Sec.  23.755(a)(2) flightcrew
visibility requirement is more directly related to flightcrew interface
than occupant environment. The FAA is including the words ``including
pilot view'' in Sec.  23.2600(a). This change harmonizes Sec.
23.2600(a) more closely with proposed CS 23.2600(a).
    Similarly, the FAA relocates the proposed Sec.  23.755(b)(2)
requirement to Sec.  23.2600(c), because this change harmonizes Sec.
23.2600(c) more closely with EASA's proposed CS 23.2600(d).
Additionally, the FAA adopts the language in EASA's proposed CS
23.2600(d), except for the spelling of ``aeroplanes'' versus
``airplanes'' for improved clarity and harmonization.
    The Associations suggested the FAA delete the word ``any'' from the
phrase ``any maneuvers within the operating limitations of the
airplane,'' in proposed Sec.  23.755(a)(2). The commenters did not
provide a rationale for this suggestion.
    The FAA disagrees as removing the word ``any'' could unduly
restrict the scope of the rule. The FAA's intent is that adequate
visibility must be provided to perform any maneuvers within the
operating limitations of the airplane. Therefore, the FAA adopts Sec.
23.2600(a) as proposed in the NPRM.
    The Associations, Transport Canada, EASA, and ANAC questioned
proposed Sec.  23.755(a)(3), which would require the airplane design to
protect the pilot from serious injury due to high-energy rotating
failures. The Associations stated there may be new systems which may
include high amounts of energy that is not the result of rotating
equipment. The commenters suggested proposed Sec.  23.755(a)(3) be
broadened to include the new systems, such as high voltage systems.
EASA similarly suggested amending the protection of pilots against
serious injury due to high-energy rotating failures to include any
high-energy risks.
    The FAA has considered the commenters' suggestion to change
proposed Sec.  23.755(a)(3) as recommended. However, the FAA has
concluded that the safety requirements contained in Sec.  23.2510,
``Equipment, systems and installations,'' (proposed as Sec.  23.1315)
of this rule adequately address hazards from high-energy sources.
Therefore, no change is being made to the final rule based on the
commenters' suggestion.
    ANAC referenced former Sec.  23.1461(d) and asked the FAA to
explain why proposed Sec.  23.755(a)(3) excluded protection for
airplane occupants other than the pilot from certain hazards.
Additionally, Transport Canada commented the proposed language requires
protecting the pilot from high-energy rotating failures, which suggests
a lower level of safety for the other airplane occupants. It
recommended replacing the word ``pilot'' with ``occupants''.
    The FAA agrees with ANAC and Transport Canada that proposed Sec.
23.755(a)(3) would effectively lower the level of safety because it did
not protect all occupants from high-energy rotor failures. It also did
not protect the airplane from high-energy rotor failures, and allowed
the pilot and pilot controls to be in the inboard propellers' plane of
rotation. The FAA intended to incorporate the safety intent of former
Sec. Sec.  23.771(c) and 23.1461.
    Therefore, the FAA adopts Sec.  23.2550 to better capture the
safety intent of former Sec.  23.1461. Section 23.2550 requires
equipment containing high-energy rotors to be designed or installed to
protect the occupants and airplane from uncontained fragments. The FAA
also revises Sec.  23.2320(a)(2) (proposed as Sec.  23.755(a)(3)) to
capture the safety intent of former Sec.  23.771(c). Section
23.2320(a)(2) will require the pilot and flight controls be protected
from propellers.
    Textron and NJASAP commented on the requirement in proposed Sec.
23.755(b)(1) for level 4 airplanes to ensure that the windshield and
its supporting structure directly in front of the pilot can withstand
the impact equivalent of a two-pound bird. Textron noted the 14 CFR
part 33 engine requirement for medium bird ingestion is based on a 2.5-
pound bird and questioned why the FAA did not use 2.5-pounds in
proposed Sec.  23.755(b)(1). Textron also recommended the FAA consider
language from CS 23.440(a) with weight/type specifics being defined in
the industry standards.
    The FAA notes NJASAP's and Textron's comment on the weight of the
bird in proposed Sec.  23.755(b)(1). Former Sec.  23.775(h)(1) required
windshield panes directly in front of pilots in the normal conduct of
their duties, and the supporting structure for these panes, to
withstand, without penetration, the

impact of a two-pound bird when the velocity of the airplane (relative
to the bird along the airplane's flight path) is equal to the
airplane's maximum approach flap speed for commuter category airplanes.
The FAA codified this requirement in part 23, amendment 23-49.\39\ The
preamble of the NPRM \40\ for amendment 23-49 explains that the two-
pound bird requirement was based on ICAO bird strike data that occurred
on airplanes of 19,000 pounds or less from 1981 through 1989. Also,
this requirement is well established in the former regulations and has
provided an acceptable level of safety. Therefore, the FAA retains the
two-pound bird requirement.
---------------------------------------------------------------------------

    \39\ Final Rule, Airworthiness Standards; Systems and Equipment
Rules based on European Joint Aviation Requirements, 61 FR 5151,
5166 (Feb. 9, 1996).
    \40\ NPRM, Airworthiness Standards; Systems and Equipment Rules
based on European Joint Aviation Requirements (59 FR 37620, July 22,
1994).
---------------------------------------------------------------------------

    NJASAP commented the methodology used to discriminate between level
3 and 4 airplanes will motivate OEMs to certify more airplanes within
level 3. The commenter also noted that airplanes in this category have
experienced fatal accidents due to bird strikes. NJASAP recommended the
FAA apply the requirements of proposed Sec.  23.755(b)(1) to level 3
high-speed airplanes.
    The FAA acknowledges the requirement in former Sec.  23.775(h)(1)
applied to commuter category airplanes, while the proposed requirement
would have applied only to level 4 airplanes. Under the former
regulations, a commuter category airplane was limited to multiengine
airplanes with a seating configuration, excluding pilot seats, of 19 or
less and a maximum certificated weight of 19,000 pounds or less.\41\
Additionally, a normal category airplane was limited to those airplanes
that had a seating configuration, excluding pilot seats, of nine or
less, a maximum certificated takeoff weight of 12,500 pounds or less,
and intended for nonacrobatic operation.\42\ Under the proposal, level
4 airplanes would be airplanes with a maximum seating configuration of
10 to 19 passengers. Thus, the proposal would have the effect of
providing relief to a percentage of part 23 airplanes with a maximum
certified takeoff weight more than 12,500 pounds, but have fewer than
10 passengers seating configuration.
---------------------------------------------------------------------------

    \41\ See Sec.  23.3(d), amendment 23-62.
    \42\ See Sec.  23.3(a), amendment 23-62.
---------------------------------------------------------------------------

    Under NJASAP's proposal, this requirement would apply to airplanes
with 7 to 9 passengers and a maximum certified takeoff weight of 12,500
pounds or less, which would increase the certification requirements of
former Sec.  23.775(h)(1). This regulation has proven to be an
acceptable level of safety. Additionally, adding level 3 airplanes
would increase the cost for a number of these airplanes that weigh less
than 12,500 pounds.
    Transport Canada and ANAC noted that former Sec.  23.831 addresses
smoke, which was not included in proposed Sec.  23.755(c). Transport
Canada recommended the FAA add the phrase ``and solid or liquid
particulates'' after the word ``vapors'' in proposed paragraph Sec.
23.755(c) because smoke is a collection of airborne solid and liquid
particulates and gases.
    The FAA agrees with Transport Canada and ANAC and revises Sec.
23.2320(c) to require the air provided to each occupant be free of
hazardous concentrations of smoke during normal operations and likely
failures. The FAA intended proposed Sec.  23.755(c) to incorporate the
safety intent of former Sec.  23.831(b), which requires the ventilating
air in the flightcrew and passenger compartments to be free of harmful
or hazardous concentrations of gases and vapors in normal operations
and in the event of reasonably probable failures or malfunctioning of
the ventilating, heating, pressurization, or other systems and
equipment. It also requires smoke evacuation be accomplished quickly if
accumulation of hazardous quantities of smoke in the cockpit area is
reasonably probable.
    The FAA chose the term ``smoke'' instead of ``solid or liquid
particulates'' because it is a more common term. Section 23.2320(c)
requires air at a breathable pressure, free of hazardous concentrations
of gases, vapors, and smoke, to be provided to each occupant during
normal operations and likely failures.
    ANAC questioned whether general rules (like proposed Sec.  23.1315)
would address the concern of smoke evacuation capability and requested
the FAA clarify how airplane manufacturers would be driven to develop a
smoke evacuation system in case there is no explicit requirement, just
general ones.
    The FAA considers Sec.  23.2320(c) to be an explicit requirement
for cockpit smoke evacuation but general regulations may also require
smoke evacuation to be considered. A pressurized airplane design that
cannot evacuate smoke from the cockpit sufficiently to allow the
flightcrew to safely perform their duties, does not provide each
occupant with air at a breathable pressure, free of hazardous
concentrations of gases, vapors and smoke, during normal operations and
probable failures. Therefore, an effective smoke evacuation system is
necessary to comply with Sec.  23.2320(c) of this rule.
    The Associations recommended reordering proposed Sec.  23.755(d)
and (e) to place the oxygen requirements after the pressurization
requirements. The FAA agrees with the recommendation and notes this
change harmonizes with EASA's regulation. In EASA's regulation,
pressurization system requirements precede the oxygen systems
requirements.
    Textron commented that the FAA should remove proposed Sec.
23.755(e)(1), as it covers the same subject area as proposed Sec.
23.1305(c). Proposed Sec.  23.1305(c) would have required information
concerning an unsafe system operating condition to be provided in a
timely manner to the crewmember responsible for taking corrective
action. Presentation of this information must be clear enough to avoid
likely crewmember errors.
    The FAA agrees with Textron's comment, as both sections would
require the crewmembers to be made aware of unsafe conditions.
Therefore, the FAA adopts Sec.  23.2605(c) as proposed and withdraws
proposed Sec.  23.755(e)(1).
    Proposed Sec.  23.755(e)(2) would have required pressurization
systems, if installed, to include a pressurization system test. The FAA
intended to capture the safety intent of former Sec.  23.843,
``Pressurization system tests,'' which required specific tests for
demonstrating compliance with safety requirements. Upon further review,
the FAA finds that proposed Sec.  23.755(e)(2) contains prescriptive
requirements, which is inconsistent with the FAA's goal of establishing
performance-based requirements as was set forth in the NPRM. Therefore,
the FAA withdraws proposed Sec.  23.755(e)(2).
    The FAA reviewed the former regulations related to proposed Sec.
23.755 to determine if it inadvertently omitted any safety requirements
for pressurization systems. As a result of this review, the FAA has
identified the following omissions, which are addressed in this rule.
    This final rule now requires pressurization systems, if installed,
to be designed to protect against decompression to an unsafe level,
which captures the safety intent of former Sec. Sec.  23.841(c), (d)(2)
and (d)(3). This final rule also requires pressurization systems, if
installed, to be designed to protect against excessive differential
pressure, which captures the safety intent of Sec. Sec.  23.841(b)(1),
(b)(2), (b)(3) and (b)(8).

    Section 23.2320(e)(1) specifically requires that if an oxygen
system is installed in the airplane, it must effectively provide oxygen
to each user to prevent the effects of hypoxia and be free from hazards
in itself, in its method of operation, and its effect upon other
components. This requirement captures the safety intent of former
Sec. Sec.  23.1441(a) and (d); 23.1443, and 23.1447(a), (b), (c), (d),
(e), and (g). These provisions require pressure/demand oxygen equipment
for the crew on high altitude airplanes; minimum oxygen flowrates and
pressures at specified conditions; standards for oxygen mask and
cannula effectiveness; ease of donning, retention, and accessibility;
and standards for crew communication while using oxygen equipment.\43\
The FAA revises 23.2320(e)(1) to capture the safety intent of these
former regulations, but without their prescriptive requirements, by
requiring that if an oxygen system is installed in the airplane, it
must effectively provide oxygen to each user to prevent the effects of
hypoxia.
---------------------------------------------------------------------------

    \43\ These specifications were intended to protect against
hypoxia.
---------------------------------------------------------------------------

    The FAA has also decided to add the specific language from former
Sec.  23.1441(b) into Sec.  23.2320. Requiring an oxygen system, if
installed, to be free from hazards in itself, in its method of
operation, and its effect upon other components restates former Sec.
23.1441(b) verbatim and captures the safety intent of former Sec. Sec.
23.1441(b) and (e), 23.1445, 23.1447(f), 23.1449, 23.1450(b), 23.1451,
and 23.1453. These provisions required--
     A means for the crew to turn on and shut off oxygen supply
at the high-pressure source in flight;
     Materials that could be used for oxygen tubing to be
considered;
     A means to reserve oxygen for the flightcrew if a source
is shared with passengers;
     A manual means to deploy passenger oxygen masks (or other
units) for high-altitude airplanes;
     A means to allow the crew to determine whether oxygen is
being delivered;
     Hazards from chemical oxygen generator temperature and
pressure to be addressed;
     Protection of oxygen equipment and lines from fire
hazards; and
     Protection against overload, unsafe temperatures, and
hazards in a crash landing.
    The FAA withdraws proposed Sec.  23.755(d)(1) as it is rendered
redundant by adopted Sec.  23.2600(b).\44\ Furthermore, by making the
revisions described previously, the FAA is able to eliminate proposed
Sec.  23.755(d)(2) and (3) as redundant. Proposed Sec.  23.755(d)(2)
and (3) would have required oxygen systems to include a means to
determine if oxygen is being delivered and a means to permit the
flightcrew to turn on and shut off the oxygen supply at any high-
pressure source in flight. The FAA considers these requirements
redundant because failure to deliver oxygen to a user who needs oxygen
for protection against hypoxia with no way to determine that oxygen is
not flowing is a hazard in the oxygen system; and an oxygen leak that
cannot be shutoff at the high pressure source is a hazard in the oxygen
system. If oxygen is needed for the survival of the pilots or
passengers and it is turned off at the high-pressure source
(intentionally or inadvertently), the inability to turn it on would be
a hazard in the oxygen system.
---------------------------------------------------------------------------

    \44\ Proposed Sec.  23.755(d)(1) would have required oxygen
systems to include a means to allow the flightcrew to determine the
quantity of oxygen available in each source of supply on the ground
and in flight. Adopted Sec.  23.2600(b) requires the applicant to
install displays so qualified flightcrew can monitor and perform
defined tasks associated with the intended functions of systems and
equipment.
---------------------------------------------------------------------------

f. Fire Protection (Proposed Sec.  23.800/Now Sec.  23.2325)
    In the NPRM, proposed Sec.  23.800 (now Sec.  23.2325) would have
required the--
     Insulation on electrical wire and electrical cable outside
designated fire zones be self-extinguishing;
     Airplane cockpit and cabin materials in certification
levels 1, 2, and 3 be flame-resistant;
     Airplane cockpit and cabin materials in level 4 airplanes
be self-extinguishing;
     Airplane materials in the baggage and cargo compartments,
which are inaccessible in flight and outside designated fire zones, be
self-extinguishing; and
     Electrical cable installation that would overheat in the
event of circuit overload or fault be flame resistant.
    Additionally, proposed Sec.  23.800 would have precluded thermal
acoustic materials outside designated fire zones from being a flame
propagation hazard. Proposed Sec.  23.800 would have also required
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 have required 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 have required 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
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 have required 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 have also required combustion heater
installations outside designated fire zones be protected from
uncontained fire.
    EASA commented that the fire protection outside designated fire
zones requirements proposed in Sec.  23.800 were design solutions
instead of objectives. EASA contended these proposed provisions would
hamper the development of different, but acceptable future designs.
EASA recommended the FAA follow the A-NPA text from CS 23.445.
    The FAA does not share EASA's view that the proposed Sec.  23.800
requirements were design specific solutions. For the foreseeable
future, there will be wiring, cabling, insulating, and covering
materials used in airplane cabins, cockpits, and baggage and cargo
compartments. The performance standard requires certain materials be
self-extinguishing, flame resistant, etc., in order to prevent the
initiation or propagation of a fire. The way to demonstrate compliance
with the performance standard is now moved to accepted methods of
compliance instead of being specified in rule language or appendices.
Additionally, the former part 23 regulations for commuter category
airplanes, and the proposed regulations for level 4 airplanes, intended
for personnel to be alerted to the presence of a fire and a way to
extinguish it. Based on the FAA's understanding of the current
technology available, for the foreseeable future, fire detection
systems and extinguishers are the methods to achieve this. The FAA is
not prescribing the technology and design of those systems.

    Additionally, the FAA finds that following the A-NPA text from CS
23.445 would be a new approach to achieving the safety intent of
preventing the initiation or propagation of a fire, which was not set
forth for notice and comment. Further, the FAA has concerns whether
EASA's proposed rule language would meet the same level of safety as
provided for in the former part 23 regulations, as EASA's proposed text
would require minimization of the risk of ``fire initiation'' and
``fire propagation''. The word ``minimize'' has not historically been
used in this safety standard where specific tests were used with
specific pass/fail criteria. The FAA also finds using the word
``minimize'' may introduce ambiguity in the rule. While the FAA is not
adopting EASA's recommendation, the FAA contends the requirement in
Sec.  23.2325 harmonizes with EASA's requirements because the effect is
the same.
    Embraer recommended modifying the title of proposed Sec.  23.800 to
remove the word ``designated,'' as well as removing the phrase
``Outside designated fire zones'' from the lead sentence of the
proposed rule.
    The FAA agrees with Embraer's comment that it is unnecessary to
state ``designated'' in the title. The FAA eliminates the phrase ``fire
zones'' as well because the term may lead to confusion. This revision
aligns the final rule with the safety intent of former regulations and
has the benefit of aligning the title with EASA's proposed title.
Furthermore, the FAA changes the title of Sec.  23.2325 to ``Fire
protection'' and deletes the lead-in sentence ``Outside designated fire
zones:''. Finally, the FAA adds ``. . . in the fuselage . . .'' to
subparagraph (c) so as not to expand the applicable area of the rule.
    Transport Canada recommended the FAA define several terms used in
this section, specifically, ``self-extinguishing,'' ``flame
resistant,'' and ``flame propagation hazard'', because this section
would otherwise be subject to a wide range of interpretation. Transport
Canada stated the performance statement, as expressed, may not ensure
the level of safety of former Sec.  23.853.
    The FAA finds that defining these terms is not necessary, nor that
this rule will be subject to a wide range of interpretation. Putting
the parameters necessary to precisely define these terms would mean
specifying test standards, which is contrary to the rule's intent to
move away from prescriptive standards. The specifications for meeting
these requirements will be contained in an accepted means of
compliance. One means of compliance accepted by the FAA is to use the
former prescriptive means of compliance contained in former part 23,
together with a policy statement issued by the FAA identifying means by
which the FAA has addressed errors, ELOS findings to various provisions
of former part 23, and special conditions (i.e., ``prescriptive
means''). The performance standard, plus this accepted means of
compliance, will ensure the same level of safety as former Sec.
23.853. The FAA notes that to be acceptable, any future proposed means
of compliance would have to provide at least an equivalent level of
safety.
    Transport Canada questioned whether proposed Sec.  23.800(a) would
cover components located in between the fuselage skin and the
compartment liners that were explicitly covered under former Sec.
23.853. The commenter recommended the FAA consider these components.
    The FAA finds it unnecessary to list these specific parts in the
rule since all materials in those compartments must meet the standards
specified for that compartment. The FAA notes, just as under former
Sec.  23.853(d)(3)(ii), items behind compartment liners are considered
materials that exist in those compartments.
    In level 4 airplanes, proposed Sec.  23.800(a)(3) would have
required materials in the cockpit, cabin, and baggage and cargo
compartments be self-extinguishing. NJASAP stated level 3 high-speed
airplanes should also be required to have self-extinguishing cockpit
and cabin materials. NJASAP noted many business jets that fly at high
altitude will fall into the level 3 high-speed category in the future.
NJASAP indicated if a fire were to break out in this airplane type, it
could take several minutes to detect it and to make an emergency
landing.
    The FAA notes under the former Sec.  23.853(d), only commuter
category airplanes needed to meet the self-extinguishing requirement
for these specified items. In the NPRM, the FAA correlated level 4
airplanes to the commuter category. Therefore, adding the requirement
to make cockpit and cabin materials self-extinguishing for level 3
airplanes would impose requirements beyond those imposed under former
Sec.  23.853 and would be beyond the scope of the notice. Furthermore,
the FAA is unaware of service experience with level 3 airplanes that
would justify the increased cost associated with the NJASAP's comment.
    Textron and the Associations requested clarification regarding the
use of ``or'' in proposed Sec.  23.800(b)(2) with respect to circuit
overload or fault. The Associations asked whether the FAA intends to
allow some electrical systems, such as high-reliability primary power
wires in electrically-powered airplanes, to use reliable design
practices in place of circuit protection for some wires. Textron
thought the use of ``or'' meant both overload and failure of the
protective device do not need to be considered and asked whether the
intent is to allow some circuits without overload protection, such as
main start cables.
    The FAA notes the focus of this rule is fire protection rather than
circuit design. The FAA's intent is to make certain electrical cable
installations that could overheat are flame resistant, regardless of
whether this is due to a circuit overload or fault. Proposed Sec.
23.800 nearly mirrors former Sec.  23.1365(b), which used the same
phrase ``. . . circuit overload or fault . . . .'' \45\ The FAA did not
intend to change the meaning of former Sec.  23.1365(b). To address the
commenters' concerns, the FAA revises Sec.  23.2325 to reflect the
language as stated in former Sec.  23.1365(b).
---------------------------------------------------------------------------

    \45\  See 61 FR 5151, February 9, 1996.
---------------------------------------------------------------------------

    Also, the FAA noted a typographical error in proposed paragraph
(c). A slash (``/'') between ``thermal'' and ``acoustic'' was missing.
The absence of the ``/'' indicate only insulation that was both thermal
and acoustic must comply. The FAA's intention was either thermal or
acoustic, as required under the former Sec.  23.856. The FAA has
corrected this inadvertent omission in this rule.
    Textron and the Associations submitted comments on proposed Sec.
23.800(d), which would have required sources of heat that are capable
of igniting adjacent objects, to be shielded and insulated to prevent
such ignition. Textron noted the proposed rule broadened the scope of
the former requirement from ``cargo and baggage compartments'' to
anything that is not a designated fire zone. Textron recommended the
FAA modify proposed Sec.  23.800(d) to include the phrase ``located in
the cargo and baggage compartments'' after ``Sources of heat.'' Textron
also commented that preventing hot equipment from starting fires in
normal operation is needed, but in the case where materials and
proximities are controlled by type design (i.e., other than the cargo
and baggage compartments), this is sufficiently addressed by proposed
Sec.  23.1300 (now Sec.  23.2500). The Associations recommended
modifying proposed Sec.  23.800(d) by adding the

phrase ``located in the cargo compartment.''
    The FAA agrees the proposed rule would have unintentionally
broadened the prior requirements. The FAA revises the rule language to
add ``within each cargo and baggage compartment''. The FAA also agrees
with Textron that other regulations in subpart F sufficiently address
the issue of preventing hot equipment from starting fires in normal
operation where materials are located in places other than the cargo
and baggage compartments.
    The Associations proposed removing the word ``any'' in front of
``fire'' from proposed Sec.  23.800(e)(2) and (f). The commenters did
not provide a reason for the proposal. Although ``any'' is implied, the
FAA prefers to leave the word in the rule language to be explicit.
    Regarding proposed Sec.  23.800(g)(2),\46\ Textron asked whether
the probability of the leak is considered (i.e., the ``improbable''
requirement is for ignition and hazard after a leak). Textron
recommended the FAA clarify whether the requirement presumes a leak.
Transport Canada commented that the language of proposed Sec.
23.800(g)(2) was not consistent with AC 23.1309-1E. An individual
commenter submitted a similar comment. Transport Canada recommended the
FAA revise this provision to be consistent with AC 23.1309-1E, thereby
changing the qualitative probability to be remote, extremely remote, or
extremely improbable.
---------------------------------------------------------------------------

    \46\ Textron cited proposed ``Sec.  23.2325(a)(2)'', but it
appears the commenter intended to refer to Sec.  23.2325(g)(2).
---------------------------------------------------------------------------

    The FAA agrees the wording of proposed Sec.  23.800(g)(2) was
problematic because the term ``improbable'' was associated with
quantitative failure rates in former Sec.  23.1309. The FAA did not
intend to require an assessment of the probability of a flammable fluid
leak or ignition of a flammable fluid leak. The FAA's intent is that
reasonable design precautions are used to reduce (i) the likelihood of
flammable fluid leaks, (ii) the likelihood of flammable fluid ignition,
and (iii) the severity of flammable fluid ignition. The FAA agrees that
since the proposed rule would have required ignition to be assumed, it
does not make sense to make the hazard improbable ``if'' ignition
occurs.
    The FAA intended to capture the safety intent of the requirement in
former Sec.  23.863. The FAA considered the suggestions for revising
proposed Sec.  23.800(g), and is using the text of former Sec.
23.863(a). Former Sec.  23.863(a) was a performance-based requirement
and former Sec.  23.863(b) and (c) provided details on how former Sec.
23.863(a) must be addressed. New Sec.  23.2325(g)(2) requires a means
to minimize the probability of ignition of the fluids and vapors and
the resultant hazard if ignition does occur in each area where
flammable fluids or vapors might escape by leakage of a fluid system.
``Minimize'' means to reduce the probability and consequences of
occurrence to the extent practical. It does not establish a
probabilistic requirement, but rather requires application of sound
engineering judgment to use effective means to achieve the safety
objective.
g. Fire Protection in Designated Fire Zones and Adjacent Areas
(Proposed Sec.  23.805/Now Sec.  23.2330)
    In the NPRM, proposed Sec.  23.805 (now Sec.  23.2330) would have
required--
     Flight controls, engine mounts, and other flight
structures within or adjacent to designated fire zones be capable of
withstanding the effects of a fire;
     Engines inside designated fire zones to remain attached to
the airplane in the event of a fire or electrical arcing; and
     Terminals, equipment, and electrical cables, inside
designated fire zones, used during emergency procedures, be fire-
resistant.
    Embraer recommended modifying proposed Sec.  23.805 to change the
title from ``Fire protection in designated fire zones'' to ``Fire
protection in fire zones and adjacent areas.''
    The FAA agrees with the recommendation to add ``and adjacent
areas'' to the title for clarification. The FAA notes that Sec.
23.805(a) references flight controls, engine mounts, and other flight
structures adjacent to a designated fire zone.
    However, ``designated fire zone'' has a particular meaning. Embraer
viewed this proposed definition as prescriptive and recommended the FAA
use the definition of ``fire zone'' contained in the draft of AC
25.863-1. That definition stated a fire zone means a ``zone that
contains a nominal ignition source and may be exposed to a flammable
fluid/material as a result of a failure.'' The FAA reviewed the
definition of ``fire zone'' in AC 25.863-1 and determined this
definition would impose requirements beyond those in the former part 23
regulations.
    Embraer also recommended removing the modifying phrase ``inside
designated fire zones'' contained in the proposed regulation. Embraer
stated that ``former Sec.  23.1181 defined the `hot' parts of an engine
installation is an ignition source and considering that there are fuel,
oil, and hydraulic fluids being carried around such areas, they shall
be considered a fire zone, and then the term `designated' would apply,
which means that it is not necessary [for] further analysis to define
if it is a flammable fluids zone or a fire zone.''
    The FAA agrees with Embraer's recommendation and removes the
modifying phrase from the first line of the proposed text for Sec.
23.805(b). The FAA will clarify within each requirement if it applies
in designated fire zones, or designated fire zones and adjacent areas.
    EASA stated that proposed Sec.  23.805(b) reflects current design-
specific requirements that should be amended to cover other ``new''
designated fire zones, such as for batteries. Proposed Sec.  23.805(b)
would have required engines inside designated fire zones to remain
attached to the airplane in the event of a fire or electrical arcing.
EASA recommended revising proposed Sec.  23.805(b) to read: ``A fire in
a designated fire zone must not preclude continued safe flight and
landing''.
    The FAA finds EASA's proposal is beyond the scope of the NPRM. The
FAA intended proposed Sec.  23.805 to capture the safety intent of
former Sec. Sec.  23.865 and 23.1359(b). Former Sec.  23.865, in part,
required engine vibration isolators to incorporate suitable features to
ensure the engine is retained if the non-fireproof portions of the
vibration isolators deteriorate from the effects of a fire. The FAA
finds this requirement is still applicable to engines that use
flammable fuels and should be retained. However, the FAA agrees
proposed Sec.  23.805(b) reflected current design-specific requirements
that would not be applicable to other potential designs that do not use
flammable fuels for propulsion. Therefore, the FAA is making this
requirement only applicable to engines in designated fire zones. The
FAA also withdraws the proposed requirement for engines to remain
attached to the airplane in the event of electrical arcing, because the
FAA finds that the threat of electrical arcing causing structural
failure is addressed adequately in the electrical systems requirements
in subpart F.
    Embraer commented that the word ``engine'' should be replaced with
the phrase ``power unit'' in proposed Sec.  23.805(b). The FAA
understands Embraer's rationale, but the FAA's authority to issue TCs
refers to ``aircraft engines,'' not power units (49 U.S.C. 44704(a)(1))
so the term ``aircraft engines'' needs to be retained. Therefore, the
FAA is not adopting EASA's recommendation in the final rule.

    Textron recommended the FAA replaces ``terminals, equipment, and
electrical cables'' with the word ``equipment'' in proposed Sec.
23.805(c). Paragraph (c) would have required terminals, equipment, and
electrical cables inside designated fire zones, that are used during
emergency procedures, be fire resistant. Textron stated that if this
provision is supposed to apply to anything in a fire zone that gets
used in an emergency, it is potentially misleading.
    The FAA disagrees with Textron's comment. The FAA intended proposed
Sec.  23.805(c) to capture the safety intent of former Sec.
23.1359(b), which stated ``Electrical cables, terminals, and equipment
in designated fire zones that are used during emergency procedures must
be fire-resistant.'' Accordingly, the FAA is not making any change to
the language proposed in Sec.  23.805(c) (now Sec.  23.2330(c)).
h. Lightning Protection (Proposed Sec.  23.810/Now Sec.  23.2335)
    In the NPRM, proposed Sec.  23.810 (now Sec.  23.2335) would have
precluded 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
have required airplanes approved only for VFR to achieve lightning
protection by following FAA-accepted design practices found in FAA-
issued ACs and in FAA-accepted consensus standards.
    Air Tractor and Transport Canada commented that ``FAA-accepted
design practices'' does not establish a performance standard in
proposed Sec.  23.810(b). Air Tractor also noted this proposed
regulation would make the ACs required and regulatory. Transport Canada
further stated that specifying ``FAA'' in the rule is not conducive to
harmonization between authorities and recommended replacing ``FAA-
accepted design practices'' with a performance-based requirement in the
form of a safety objective.
    The FAA agrees that proposed Sec.  23.810(b) is not consistent with
the goal to develop performance-based standards and to spur innovation.
The FAA recognizes new methods of protecting the airplane from
catastrophic effects from lightning may be developed that are not
currently FAA-accepted design practices and these methods should be
permitted if found acceptable to the FAA.
    In light of the comments received for this section, the FAA
revisited the goal of proposed Sec.  23.810. The FAA intended to
capture the safety intent of the former lightning regulations in former
Sec.  23.867. Former Sec.  23.867(a) was a high-level performance-based
requirement requiring the airplane to be protected against catastrophic
effects from lightning. Former Sec.  23.867(b) and (c) were means of
compliance with Sec.  23.867(a). Former Sec.  23.867(b) specified how
metallic components must be designed to protect the airplane against
catastrophic effects from lightning, while former Sec.  23.867(c)
specified how non-metallic components must be designed to protect the
airplane from catastrophic effects from lightning. The FAA also
intended to establish safety requirements for direct and indirect
effects of lightning on all systems and structure in proposed
Sec. Sec.  23.810, 23.930, and 23.1320. Proposed Sec.  23.810 would
have addressed protection of structure, proposed Sec.  23.930 would
have addressed protection of fuel systems, and proposed Sec.  23.1320
would have addressed protection of electrical and electronic systems.
However, upon review, proposed Sec.  23.810 did not address all
structure and proposed Sec.  23.1320 did not address all systems and
equipment.
    The FAA has determined that retaining the language of former Sec.
23.867(a) would more appropriately capture the FAA's intent for Sec.
23.2335 because it applies to the entire airplane including all
systems, equipment and structure. Therefore, the FAA revises Sec.
23.2335 to require the airplane to be protected against catastrophic
effects from lightning, which is a performance standard. The FAA finds
this revision addresses Air Tractor's and Transport Canada's remaining
concerns.
    The FAA also identified an error in the proposed correlation table
in the NPRM. Former Sec.  23.867(b) was correlated with proposed Sec.
23.1320, ``Electrical and electronic system lightning protection'', and
not proposed Sec.  23.810, ``Lightning protection of structure''. This
reference was incorrect because proposed Sec.  23.1320 did not address
all aspects of protecting the airplane against catastrophic effects
from lightning for metallic components. The FAA corrected the
correlation in the table provided in this final rule.
    EASA commented that the requirement of lightning protection of the
structure should relate to the type of environment that causes the
risk, instead of the type of operation. EASA recommended replacing IFR
with instrument meteorological conditions (IMC), and replacing VFR with
visual meteorological conditions (VMC).
    The FAA agrees with EASA's comment that the requirements for
lightning protection should be related to the risk of lightning. Rather
than drawing a distinction between IFR and VFR, or IMC and VMC, the
language provided in this final rule now reflects a performance-based
standard. The standard will be met by an accepted means of compliance.
The FAA finds this approach provides greater flexibility to allow
development of means of compliance that are appropriate for different
types of airplanes and different types of operation depending on the
risk of lightning.
6. Subpart E--Powerplant
a. General Discussion
    In the NPRM, the FAA proposed substantial changes to former subpart
E based on two considerations. First, the FAA stated many of the former
regulations could be combined to provide fewer regulations that
accomplish the same safety intent. Second, the FAA also stated part 23
overlaps with the requirements in parts 33 and 35.
    Textron noted that subpart E appeared to be missing performance
requirements for key propulsion aspects. Textron recommended the FAA
include rules that address engine controls, powerplant accessories and
components, and powerplant instruments and indicators as set forth in
former Sec. Sec.  23.1141, 23.1163, and 23.1225 of appendix E of the
Part 23 ARC Report.
    The FAA reviewed each requirement mentioned by the commenter and
finds those requirements have been addressed in the final rule using
less prescriptive language. In most cases several regulations, rather
than any single rule, capture the intent of the former regulations
referenced by the commenter. Requirements contained in regulations for
powerplant installation, airplane level systems, and flightcrew
interface combined with more specific requirements found in regulations
for powerplant fire protection, instrument markings, control markings,
and placards, address the specific requirements noted by the commenter.
    An individual commenter stated the FAA's removal of all references
to part 33 and part 35 from proposed part 23 was inappropriate. The
commenter contended the FAA's conclusion that those references are
redundant because the requirements are already addressed during the
certification of the engine or propeller is incorrect. The commenter
noted that compliance with specific performance standards for engines
and propellers is only ensured by requiring a product to be approved to
a specific

amendment level of part 33 or 35, before it is eligible for
installation on a particular airplane. The commenter also noted that
engines and propellers approved prior to a specific part 23 amendment
level may not have met a specific installation level requirement
specified by that amendment. For example, the commenter noted that
former Sec.  23.903 required minimum engine ingestion performance by
the installation of an engine certified to a specific amendment level
of part 33, thereby ensuring that any installed turbine engine had met
a minimum performance level mandated by the FAA through that amendment
level.
    The individual commenter also stated engine and propeller
limitations are established during the type certification of the engine
or propeller, and that these limitations are required to be included in
the TCDS and associated installation manuals. The installer must comply
with these limitations. The commenter further implied that, if the
installed engine or propeller limitations cannot be complied with, safe
operation of the product cannot be ensured. For example, the commenter
stated that former Sec. Sec.  23.1041 through 23.1047 required the
engine installation to be designed such that the temperature
limitations--established under part 33 for the engine--are maintained
in the installed configuration.
    The individual commenter also noted that some components of an
engine or propeller are approved at both the engine or propeller level
and at the airplane level, but that all components require approval at
the airplane level. According to the commenter, the approval of the
engine or propeller TC can include items such as a propeller reversing
system or a turbocharger, and this data can be used for approval of
these systems at the airplane level. If an applicant prefers approval
at the airplane level only, this commenter noted, the former rule
provided a reference to the requirements contained in part 33 or 35, as
appropriate. Without the inclusion of these references in proposed part
23, certification may require special conditions.
    The commenter recommended the FAA include--
     References to parts 33 and 35 for type certificated
engines and propellers being installed and consider the inclusion of
similar standards when the installation of non-type certificated
engines or propellers are permitted;
     A specific rule stating the powerplant installation design
must be such that all installed type certificated engines and
propellers remain within their respective approved limitations and
installation manual requirements and that a similar provision be
included when the installation of non-type certificated engines and
propellers is permitted; and
     Reference in the proposal to the applicable provisions of
parts 33 and 35 for engines, propellers, and any related components of
those products being installed only at the airplane level.
    The FAA agrees with the general intent of the commenter. The FAA
notes that while some requirements in the former part 23 indeed overlap
with those of parts 33 and 35, the FAA did not intend to imply that
compliance with those requirements necessary for type certification of
an engine or propeller were no longer applicable to the certification
of the installed configuration of a type certificated engine or
propeller. Historically, TCs have been required for engines and
propellers installed in airplanes certificated under part 23 and this
rule retains this requirement for all airplanes certificated under part
23, with the exception of level 1 low-speed airplanes.\47\ Essentially,
this requirement makes the requirements in parts 33 and 35 for type
certificated engines and propellers applicable to the certification of
airplanes under part 23, because the part 33 and 35 requirements must
be met in order to install these engines and propellers on part 23
airplanes. As a result, data used to show compliance for an engine or
propeller TC is considered FAA approved, and can be used to show
compliance with any applicable part 23 requirement. In many cases, this
permits a single showing of compliance such that a re-showing of
compliance at the airplane installation level may not be required.
Approval of some components, such as propeller controls or
turbocharges, have been permitted at the airplane level by referencing
the applicable part 33 or 35 requirements and using those requirements
as an acceptable means of compliance. This certification approach will
continue to remain acceptable.
---------------------------------------------------------------------------

    \47\ Discussed in the preamble discussion for Sec.  23.2400.
---------------------------------------------------------------------------

    The FAA does not intend to accept a means of compliance for an
engine or propeller installation that would result in a level of safety
lower than that set forth in a part 33 or 35 amendment level
specifically referenced in former part 23.
    Limitations set forth in the approval of an engine or propeller
must be maintained in the installation on the part 23 airplane. These
operating limitations are established in accordance with Sec. Sec.
33.7 and 35.5. Installation instructions are provided to the installer
in accordance with Sec. Sec.  33.5 and 35.3. This regulation does not
change this approach.
    Additionally, the FAA is adding a requirement from existing Sec.
23.901(e) to Sec.  23.2400, requiring installed powerplant components--
which include engines and propellers--to meet the FAA-approved
component limitations and installation instructions, or be shown not to
create a hazard. This requirement will ensure that any operating
limitations and installation instructions applicable to the engine or
propeller remain applicable to the certification of the airplane.
    In the NPRM, an exception permitting the installation of non-type
certificated engines and propellers as part of the airplane was
proposed for simple airplanes. The proposal mirrors the precedent
established for the certification of airplanes under EASA CS-VLA. The
rule slightly expands the relief provided by the proposal, and permits
the certification of engines as part of the airplane for level 1 low-
speed airplanes. This change encompasses the same class of airplanes as
originally proposed while removing the restriction that these airplanes
be limited to VFR-only operations.\48\
---------------------------------------------------------------------------

    \48\ Discussed in the preamble discussion for Sec.  23.2400.
---------------------------------------------------------------------------

    In response to the individual commenter's concerns that the
proposal does not require certain engines to meet a specific amendment
level of part 33, as set forth in former regulations, and the
commenter's specific concern that engine ingestion performance was not
specifically addressed, the FAA notes those sections of former subpart
E that required compliance with a specific amendment level for an
engine installation are addressed in this performance-based rule. The
engine ingestion requirements of former Sec.  23.903(a)(2), for
example, are addressed by the performance-based requirements of Sec.
23.2400(c). The former rule specified that an applicant must construct
and arrange each powerplant installation to account for likely
operating conditions including foreign object threats and likely
hazards in operation. Although Sec.  23.2400(c) does not refer to a
specific requirement or amendment level of part 33, the FAA expects the
means of compliance with this regulation will include provisions for
certificating engines with acceptable foreign object ingestion
performance as required by former Sec.  23.903(a)(2), which may include
references to different amendment levels of part 33 where appropriate.
Additionally, the FAA

intends to accept part 23 through amendment 23-62, which contained
references to specific requirements in part 33, as a means of
compliance to the performance-based requirements of this rule. The FAA
will only accept a means of compliance for a performance-based
regulation that encompasses the safety intent of a former regulation
requiring compliance with a particular amendment level of part 33 or
35, if that means of compliance provides a level of safety equivalent
to the level of safety found in former part 23.
b. Powerplant Installation and Propeller Installation (Proposed
Sec. Sec.  23.900 and 23.905/Now Sec.  23.2400)
    In the NPRM, proposed Sec. Sec.  23.900 and 23.905 (now Sec.
23.2400) would have clarified, for the purpose of this subpart, that
the airplane powerplant installation must include each component
necessary for propulsion, affects propulsion safety, or provides
auxiliary power to the airplane. Proposed Sec.  23.900 would have
required the applicant to construct and arrange each powerplant
installation to account for likely hazards in operation and
maintenance, and, except for simple airplanes, each aircraft engine
would have to be type certificated. Proposed Sec.  23.905 would have
retained the requirement that each propeller be type certificated,
except for propellers installed on simple airplanes. Proposed Sec.
23.905 would have retained the requirement that each pusher propeller
be marked so it is conspicuous under daylight conditions.
    EASA commented that design-specific requirements for propeller
installations should be covered by proposed Sec.  23.900, not proposed
Sec.  23.905.
    The FAA adopts the regulatory approach taken by EASA for propeller
installation. Under this approach, the FAA includes the requirements
for propeller installation within Sec.  23.2400. Specifically, the
requirements of proposed Sec.  23.905(a) are addressed by Sec.
23.2400(b), proposed Sec.  23.905(b) are addressed by Sec.
23.2400(c)(3), and proposed Sec.  23.905(c) are addressed by Sec.
23.2400(c)(4). These revisions also clarify that a propeller
installation must not deviate from any limitations or installation
instructions as required by Sec.  23.2400(e). Addressing propeller
installation requirements in the section of the rule that establishes
powerplant installation requirements also results in closer
harmonization of the rule with EASA's proposed requirements in NPA
2016-05.
    The FAA received numerous comments regarding the issue of whether
``power units'' should be certified under part 23 as part of the
airplane type certification. The Associations noted the proposed
language would allow engine and propellers that meet required standards
to be certified as part of the airframe, provided the airplane is
certificated as a simple airplane. The commenters contended the ability
to certificate these components as part of an airframe should be based
on the complexity of the components rather than on the certification or
performance levels of the airplane in which they are installed. The
commenters supported permitting the certification of engine and
propellers that comply with traditional engine and propeller type
certification requirements either through the issuance of a standalone
TC or through the certification process for the airframe. The
commenters also noted since electric propulsion is ``on the threshold
of becoming mainstream'', the ability to certify engines and propellers
as part of the airframe is critical to the successful and safe
integration of that technology.
    EASA asserted the need to type certify an engine should be
addressed by part 21; therefore, the powerplant either could be type
certificated or certified as part of the airplane. EASA noted the type
certificate-related design and production controls that are part of the
current type certification process are also expected to be applicable
for other components such as batteries and converters. EASA stated
certification of the engine should not be related to the size or speed
of the airplane; therefore, EASA did not support limiting the
installation of propulsion systems that are not individually type
certificated to airplanes classified as simple airplanes.
    Textron noted the purpose of the proposed rule is to enhance the
ability to introduce new technology efficiently, and contended that
treating each powerplant installation (e.g., electric propulsion) using
a unique ELOS finding would not be an effective way to address the
issue. Textron recommended either adding the requirements for
certifying the power unit as part of the airplane, or changing and
including the specific requirements in the industry standard to avoid
the need for unique ELOS findings. Additionally, Textron recommended
adopting proposed CS 23.500(b), which would not restrict the
installation of non-type certificated engines that meet an industry
standard to simple level 1 airplanes.
    An individual commenter expressed support for the proposal to not
require certified engines for ``simple'' airplanes, but suggested
expanding the definition of ``simple'' to at least four-seat airplanes
with VS0 < 55kts and permitting IFR operations. The
commenter stated certain airplanes should not require a type-certified
engine with all of the associated costs, paperwork, and outdated
technology. The commenter also noted the requirement for a certified
engine in most airplanes precludes the use of electric propulsion in
anything but ``simple'' airplanes, since part 33 does not allow for the
certification of electric motors. The commenter also suggested
revisions to part 33 aimed at realizing the same kind of cost
reductions and to allow certain technologies on small airplane engines
without requiring full authority digital engine control (FADEC) levels
of ``design assurance.'' Additionally, other commenters specifically
recommended the proposed regulation be revised to permit all power
units installed in airplanes certificated in accordance with part 23 to
be type certificated or meet accepted specifications.
    Air Tractor questioned whether alternative types of powerplant
units would receive a TC specific to that unit ``from within part 23''
and distinct from the airplane in which it is installed. If so, Air
Tractor expressed concern this approach would create a series of rules
for the purpose of issuing a TC for an unconventional powerplant design
and stated part 23 rules should not be applied to the certification of
unconventional powerplants. Air Tractor also recommended all engines
and propellers be either ``type certified'' or ``possess a type
certificate.''
    NATCA noted if neither the engine nor the propeller would be
required to be type certified when installed on a simple airplane, it
is unclear how those products would be approved. Furthermore, NATCA
noted by allowing non-certificated engines on simple level 1 airplanes,
it was unclear how an airworthiness directive would be issued if an
unsafe condition were found to exist on the engine. NATCA also
recommended the FAA specify the minimum level of engineering safety
certification testing necessary to demonstrate how the engine and
propeller for simple airplanes could be approved, if they were not type
certificated.
    The FAA notes the recommendation to expand the scope of proposed
Sec.  23.900 to permit all engines and propellers installed in
airplanes certificated under part 23 to be certificated under the TC of
the airplane in which the engine or propeller is installed. The FAA
evaluated the commenters' recommendations to base the need for an
engine or propeller TC on the complexity of the powerplant

system rather than on the complexity of the airplane. The FAA has
established standards in parts 33 and 35 that ensure an acceptable
level of safety and adequate standardization for certification of all
aircraft engines and propellers. Certification of an engine or
propeller with the airplane instead of requiring a separate engine or
propeller TC essentially requires a showing of compliance equivalent to
the airworthiness standards contained in part 33 for aircraft engines
or part 35 for propellers. The FAA finds that placing these
requirements in part 23 and using an accepted standard as a means of
compliance (with the limited exception for airplanes that can be
certificated as level 1 low speed), would not significantly reduce the
regulatory burden on engine and propeller manufacturers. Additionally,
at this time the FAA does not want to place the administrative
responsibility for the certification of all engines and propellers
installed in part 23 airplanes on two separate Aircraft Certification
Directorates, with the ensuing risks of delaying implementation of the
significant changes set forth in this final rule and creating the
possibility of differing interpretations or regulatory requirements.
The FAA is, however, open to revisit this option in the future. If, for
example, actual certifications or advances in technology indicate that
expanding this approach to include larger airplanes would provide a
manufacturer certification efficiencies, the FAA would be willing to
consider this expanded approach.
    The FAA notes the Engine and Propeller Directorate (EPD) has been
responsible for establishing standards for engines and propellers and
continues to remain the best source for developing policy and guidance
for determining compliance with those standards, to include standards
for the certification of electric engines. While many commenters
believe the introduction of electric engines is imminent, and shifting
the responsibility for the certification of all engines and propellers
installed in airplanes that meet the airworthiness standards of part 23
from the EPD to the Small Airplane Directorate (SAD) would facilitate
certification of those engines, the FAA finds such action could delay
both the certification of electric engines and other more conventional
engine designs. Such a realignment of certification responsibilities
would increase the burden on both applicants and the FAA as the
involvement of two directorates would be required during the
certification process for aircraft engines and propellers.
Additionally, certification of an engine or propeller with the airplane
increases the burden of showing compliance when the product is
installed in multiple airplane models, as compliance with the basic
engine and propeller requirements must be shown for each specific
airplane model installation.
    Accordingly, the FAA retains the basic approach discussed in the
NPRM requiring that all engines and propellers require a separate TC
except for those engines and propellers installed in airplanes that can
be certificated as level 1 low speed. Those standards permit the
certification of the engine and propeller with the airplane and do not
require those products possess a separate TC. However, the FAA has
slightly revised the proposal to expand the approval of aircraft
engines and propellers under the airplane TC from simple airplanes, as
originally proposed to all level 1, low-speed airplanes. Section
23.2400 will allow level 1 airplanes with engines not separately type
certificated to be used for both VFR and IFR operations. Additionally,
the FAA has added language that indicates an acceptable standard for
the certification of an engine or propeller, contains airworthiness
criteria the Administrator has found appropriate and applicable to the
specific design and intended use of the engine or propeller, and
provides a level of safety acceptable to the FAA. This language mirrors
the language contained in former Sec.  21.17(f)(1) for primary category
aircraft whose engines and propellers are certificated under the
airplane TC. This approach allows some streamlining for the engine
approval based on a specific installation verses the generic engine TC
which might be more thorough to account for the possible installation
variables. The FAA's concept of the safety continuum in this context
bases certification requirements on potential risk and considers the
number of potential passengers and the performance of the airplane,
rather than the complexity of the engine or propeller installed.
    As future aircraft engines and energy sources become available,
both SAD and EPD may utilize ELOS findings, special conditions, and
exemptions to establish appropriate certification standards. These
processes will assist the agency in developing standards to address new
and novel technology, and can be applied regardless of whether the
design approval for an engine or propeller occurs as the part of the
airplane or as a separate engine or propeller approval. Additionally,
in response to those commenters concerned with the approval of electric
aircraft engines, part 33 airworthiness standards will be developed to
address those products as they are presented to the FAA for type
certification. Currently those standards do not exist in part 33,
therefore, special conditions will likely be used to establish
standards for the issuance of a TC before those standards have been
promulgated.
    In response to commenters' concerns related to uncertainty as to
what minimum level of testing would be required for approval of engines
not separately type certificated and how potential airworthiness
concerns would be addressed for those products, the FAA expects any
engine or propeller will meet standards that provide a level of safety
at least equivalent to that achieved with the certification of those
products today. The FAA may accept or reject any means of compliance
proposed for acceptance and will only accept a means of compliance that
ensures the design meets the performance standards set forth in part
23. An applicant intending to use this approach would have to re-
establish compliance for the specific non-type certificated product in
accordance with an applicable FAA accepted standard under the TC of
each airplane model in which the product is installed rather than only
once as would occur with an engine or propeller TC. As stated earlier,
this provision permitting the type certification of both the engine and
propeller under the airplane TC is limited to level 1 low-speed
airplanes. Any unsafe condition related to ``non-TC'd'' engines or
propellers will be addressed by issuance of an airworthiness directive
requiring corrective action against the airplane TC under which those
engines or propellers have been approved.
    Textron questioned whether proposed Sec.  23.900(c) includes
auxiliary power units, as those units are not type certificated, but
instead meet a TSO. Textron requested proposed Sec.  23.900(c) be
clarified to indicate it would apply to each aircraft power unit ``used
for propulsive power.'' Embraer, however, suggested including an
alternate means of compliance in proposed Sec.  23.900(c) for electric
engines, auxiliary power units, and other alternate sources of
propulsion.
    The FAA revises the rule to ensure APUs may be approved under the
airplane TC in accordance with a standard accepted by the FAA, such as
a TSO. The FAA does not intend to require a TC for these units.
    The Associations stated the proposal should include provisions to
address propulsion-specific hazards. The provisions include
environmental issues

unique to propulsion systems; ingestion of foreign object debris (FOD);
and the dangers of propulsion aspects to ground personnel. To address
their concerns, the commenters recommended revising proposed Sec.
23.900 to specifically require an applicant to account for all likely
operating and environmental conditions, including foreign objects
threats; sufficient clearance of moving parts to other airplane parts
or their surroundings; and likely hazards in operation, including
hazards to ground personnel.
    The FAA agrees with the commenters and revises the rule to
specifically require all likely operating conditions (which include
environmental conditions), including foreign object threats; sufficient
clearance of moving parts to other airplane parts and their
surroundings; and likely hazards in operation, including hazards to
ground personnel are accounted for in each powerplant installation.
Proposed Sec.  23.900(b) referred to these conditions as ``likely
hazards in operation and maintenance,'' but the FAA finds that
specifically enumerating them will facilitate development of acceptable
means of compliance. The FAA also notes that former subpart E required
that applicants address these conditions.
    To ensure compatibility between the airplanes and the power unit
design, as well as the safe operation of the power unit, ANAC
recommended including language, which would require the powerplant
installation comply with the limitations and installation instructions
provided by the power unit manufacturer. The Associations requested the
proposed section include additional requirements specifying the
installation of powerplant components that deviate from the component
limitations or installation instructions be safe and applicable
powerplant installations account for vibration and fatigue.
    The FAA agrees with the commenters' intent to ensure the safe
operation of the powerplant and has added paragraph (e) to Sec.
23.2400 to specifically require powerplant components comply with their
component limitations and installation instructions or be shown not to
create a hazard. This requirement applies to the engine, propeller, and
any other components of the powerplant installation. The rule is also
revised to require powerplant installations account for vibration and
fatigue. The FAA notes component limitations and an installation manual
should be included as part of any powerplant installation. The
evaluation of the powerplant installation should also include an
evaluation of propeller vibration and compliance with proposed
installation manual limits, as the installed propeller is a component
of the powerplant installation.
    Textron stated proposed Sec.  23.900 does not address automatic
power reserve (APR) systems. Textron recommended revising proposed
Sec.  23.900 based upon proposed CS 23.500. Textron also suggested
including specific language from appendix E from the final Part 23 ARC
Report, which states that an APR system that automatically advances the
power or thrust on the operating engine(s), when any engine fails
during takeoff, must comply with the applicable requirements of the
subpart. The FAA notes proposed Sec.  23.915 addressed the requirements
for APR systems referenced by the commenter and the FAA adopted these
requirements in Sec.  23.2415 of this rule.
    Textron contended the proposed rule language does not include
critical items from current part 23 or redefines current requirements.
For instance, Textron noted proposed Sec.  23.900(b) appears to change
the current requirement that the powerplant installation be accessible
for preflight inspection and maintenance and adds a hazard assessment
requirement. Textron recommended revising proposed Sec.  23.900(b) to
state each powerplant installation must ensure safe operation and be
accessible for preflight inspection and maintenance.
    The FAA has determined the performance-based regulations set forth
in the proposal, as revised by the changes made in this rule, address
all critical items in current part 23. With regard to Textron's
specific comments, the FAA did not intend to remove the requirement for
the powerplant installation to be accessible for preflight inspection
or require a new hazard assessment. The FAA intends that Sec.
23.2400(c) capture the current requirement that the powerplant
installation be accessible for preflight inspection. Likely hazards
include those that could result from lack of adequate preflight or
maintenance, which includes inspection. Additionally, the regulation
has not introduced a requirement to complete any hazard assessments not
required under current regulations.
    An individual commenter noted the proposed rules in subpart E only
appear to address a design review that considers failures and hazards.
The commenter elaborated by stating that unlike the current rules, the
proposed rules do not require a design review for proper operation in
the normal non-failed condition. The commenter stated this change is
not discussed in the NPRM and appears to leave gaps in the traditional
certification effort where the airplane is certified to operate
properly within the approved operating envelope. The commenter
recommended including an additional requirement to ensure all
powerplant components and systems remain within all limitations and
function properly when operated within the approved airplane operating
envelope.
    The FAA agrees the proposed regulatory language was not
sufficiently clear and revises proposed Sec.  23.900 (now Sec.
23.2400) to clarify the powerplant installation must be constructed and
arranged to account for likely operating conditions, likely hazards,
and all component limitations are maintained or otherwise shown to not
create a hazard throughout the approved operating envelope.
    Textron noted proposed Sec.  23.900(b) should require not just
powerplants, but rather all systems, and particularly those installed
in future airplanes, to account for likely hazards in operation and
maintenance. Accordingly, Textron recommended removing the specific
provisions of the proposal referring to powerplants from proposed Sec.
23.900 and revising proposed Sec.  23.1305 to address all systems.
    While the FAA agrees all systems should be designed to account for
likely hazards, the FAA notes powerplant installations have unique
requirements that may not directly apply or would be burdensome when
applied to the design of other systems. Accordingly, the FAA is not
expanding the applicability of this specific regulation to address all
systems.
    In the NPRM, the FAA proposed replacing the term ``engine'' with
``power unit,'' which would have included ``auxiliary power unit''
(APU). This change was intended to ensure new requirements would be
clearly applicable to various power sources, such as those using liquid
fuel or electrical power, and to other power sources not yet
envisioned. After further review, the FAA has determined it would be
more appropriate to retain the term ``engine'' in the final rule
because ``engine'' is used throughout 14 CFR, TCs are specifically
issued for aircraft engines, and the term ``aircraft engine'' is
specifically defined in 49 U.S.C. 40102 and 14 CFR 1.1. The operating
regulations also refer to required engine indicators and engine
maintenance, and Airworthiness Directives issued for aircraft engines,
as opposed to ``power units.'' Introducing the term ``power unit''
could lead to unnecessary confusion and potential disagreements
regarding the applicability of specific

regulatory requirements. Additionally, the FAA notes the term
``engine'' includes any device that converts any form of energy into
force that propels an airplane. The FAA finds the term ``engine'' can
be used to address both current and new sources of propulsion and
accordingly has replaced the term ``power unit'' with ``engine'', or
``auxiliary power unit'', where appropriate in this rule. The intent of
this change is to clarify the requirements of this subpart are
applicable to any device that propels an airplane regardless of its
source of power and to avoid potential conflicts with both the
statutory and regulatory definitions of the term ``aircraft engine.''
    The FAA has also added paragraph (d) to address the hazardous
accumulation of fluids, vapors or gases. This paragraph is virtually
identical to proposed CS 23.2430(b), ``Energy storage and distribution
system hazard mitigation,'' and corresponds to the safety intent of
former Sec.  23.1193(b) that addressed cowling drainage. It is designed
to ensure the hazards resulting from the accumulation of these
materials can be isolated from the airplane and personnel compartments
and these materials can be either safely contained or discharged.
c. Powerplant Installation Hazard Assessment (Proposed Sec.  23.910/Now
Sec.  23.2410)
    In the NPRM, proposed Sec.  23.910 (now Sec.  23.2410) would have
required an applicant to assess each powerplant separately and in
relation to other airplane systems and installations to show that a
failure of any powerplant system component or accessory will not--
     Prevent continued safe flight and landing;
     Cause serious injury that may be avoided; and
     Require immediate action by crewmembers for continued
operation of any remaining powerplant system.
    Several commenters expressed concern that proposed Sec.  23.910
would have been impossible to meet for certain existing airplane
designs. The FAA response to these comments is below.
    The Associations stated that proposed Sec.  23.910 should apply to
the ``likely'' failure of powerplant systems. The commenters asserted
that applying the proposed requirements to any failure would require
complete redundancy, which cannot be achieved in traditional single-
engine airplanes and smaller twin-engine airplanes. The commenters
contended the slower stall speeds and higher levels of crashworthiness
in the designs of these airplanes mitigate all but ``unlikely''
powerplant failures. These commenters recommended the FAA require the
applicant to assess each powerplant separately and in relation to other
airplane systems and installations to show that ``hazards resulting
from a likely failure of any powerplant system component or accessory
are minimized.''
    Textron stated proposed Sec.  23.910 was ``too high level'' and
would not have established adequate performance-based requirements for
an applicant to demonstrate compliance. As an example, Textron
contended that proposed Sec.  23.910(a) would have been an impossible
requirement to meet, especially for a single-engine airplane. Textron
recommended replacing the language of proposed Sec.  23.910 with
language from EASA CS 23.510, ``Powerplant Hazard Mitigation''
    EASA, Garmin, and Air Tractor stated the requirements of proposed
Sec.  23.910(a) would have been applicable to single-engine airplane
certification. Garmin stated, however, that a single-engine airplane
cannot meet proposed Sec.  23.910(a) unless the FAA clarifies the loss
of the thrust from the propulsion unit will not necessarily prevent
continued safe flight and landing. Garmin recommended the FAA either
revise proposed Sec.  23.910 or revise the definition of ``continued
safe flight and landing'' to allow for failure of the engine or
propeller in a single-engine airplane.
    Air Tractor stated proposed Sec.  23.910(a) would have ruled out
the certification of single-engine airplanes. Air Tractor observed, for
example, that under the proposed rule, if a fuel line or hose were
considered a ``system component,'' then the failure of one fuel line
that feeds the engine would certainly result in an engine failure. Air
Tractor noted that there may be similarly insurmountable scenarios
involving the controls for an engine. Air Tractor stressed the need for
clearly-written rules to prevent unforeseen interpretations of
provisions that have the potential to make the design and certification
of light airplanes much more difficult than previously, or even
impossible.
    An individual commenter stated that proposed Sec.  23.910(a)
appears to be a derivation of former Sec.  23.903(c)(1), which only
applied to multiengine installations and only required continued safe
operation of the remaining engines. The commenter asserted the proposed
rule would have increased the requirement from ``ensuring continued
safe operation of the remaining engines'' to ``ensuring continued safe
flight and landing of the airplane.'' The commenter further noted
proposed Sec.  23.910 would have applied to single-engine airplanes
with no justification and could have resulted in elimination of some
airplanes from certification, such as large single-engine or
multiengine airplanes where rotor non-containment effects on the
remaining engine cannot be eliminated. The commenter also stated the
proposed rule would have made ``continued safe flight and landing'' a
part of the regulation, where previously it only existed in guidance
material. The commenter indicated this may make it difficult to provide
a conditional definition of the term. To ensure safe design of
multiengine airplanes, the commenter recommended using the wording of
former Sec.  23.903(c)(1) rather than requiring a system safety
approach to powerplant installation that does not permit single
failures. The commenter also recommended using the term ``minimize''
when specifying the evaluation criteria for powerplant installations.
The commenter noted that term has been used for many years, is well
understood, and best describes the regulatory intent for those
powerplant unique systems where a single failure cannot be reasonably
eliminated from the design.
    Another individual commenter said compliance with proposed Sec.
23.290 would neither be practical nor possible in all situations that
may result in a forced landing; therefore, the proposed rule should not
include a requirement for completely eliminating hazards, which the
commenter asserted is not achievable. The commenter asserted that
replacing a standard based on minimization with an absolute standard is
not an acceptable alternative. Ultimately, the commenter recommended
revising the definition of ``continued safe flight and landing'' to
allow for catastrophic outcomes of forced landings, and to either
maintain the minimization standard, or withdraw the requirement. The
commenter further noted that compliance with the proposed requirement
of absolute prevention of hazards would be impractical or impossible
for many conventional multiengine airplane configurations regarding
rotor non-containment. This is also true for all single-engine and many
multiengine airplanes regarding a propeller blade loss--especially
since the proposed rule applies to uncontained engine failure and
engine case burn-through failures for which former Sec.  23.903(b)(1)
only required the design to minimize the hazard.
    Embraer observed that for turbine or reciprocating engine rotor
failure and/or

burn-through events, there is no way to eliminate all the risks that
will prevent continued safe flight and landing. Embraer recommended
revising the language to clarify certain proposed provisions and to add
additional provisions that would require applicants to show operating
limitations, which may adversely affect rotating component structural
integrity that would not be exceeded in service. Embraer's revisions
would require design precautions to minimize hazards to the airplane in
the event of an uncontained engine rotor or rotating component failure
or a fire originating within the engine, which burns through the engine
case.
    The FAA concurs with the commenters' recommendations to revise
proposed Sec.  23.910 to make its requirements only applicable to
likely failures and to permit minimization of certain hazards, which
could prevent continued safe flight and landing. The FAA notes the
inclusion of the term ``likely'' in the requirement for the applicant
to address hazards resulting from failures is intended to place
reasonable and prudent bounds on the scope of analysis necessary to
meet the requirement and not to require consideration of all possible
failures, however remote. The scope of this analysis will be set forth
in accepted means of compliance for this regulation.
    In response to commenters' concerns that the term ``minimize'', or
the philosophy encompassed by the use of the term, will be included in
the rule, the FAA notes that the term ``minimize'' has been included in
Sec.  23.2410(a) to permit the applicant to address those hazards,
which may prevent continued safe flight and landing of an airplane,
that cannot reasonably be eliminated. The FAA will consider
incorporation by an applicant of all practical design precautions,
which minimize hazards to the airplane, associated with a particular
failure acceptable in complying with this regulation. The FAA has
historically accepted this compliance approach when a minimization of
hazards has been required. This approach provides a simple means to
continuously improve airplane safety as new technologies and design
approaches evolve. It also permits acceptance of existing designs that
cannot reasonably eliminate hazards resulting from certain failures,
even if accepted design precautions have been incorporated into the
airplane's design. Such failures could include rotor non-containment,
engine case burn-through, and engine failures on single-engine
airplane. This change specifically addresses a concern expressed by all
commenters that the proposed regulation would make it impossible for an
applicant to show compliance with the regulation for many existing
airplane designs. Additionally, the rule will continue to permit the
use of simple parts, such as fuel lines and control cables, in airplane
designs. The FAA has traditionally considered their use acceptable
without requiring redundancy where it is neither practical nor likely
that a failure of the component would occur. The FAA's revisions to the
proposed regulation account for the normal use of these types of simple
components.
    In response to the commenter who noted the term ``continued safe
flight and landing'' in proposed Sec.  23.910(a) appears to be based on
former Sec.  23.903(c), which only applied to multi-engine airplanes,
the FAA agrees that proposed Sec.  23.910(a) does not properly address
certain failures on single-engine airplanes. The FAA believes the
revisions discussed above addresses the individual's concerns.
    Textron also recommended the FAA withdraw proposed Sec.  23.910, as
its subject area overlaps with proposed Sec.  23.1315 (now Sec.
23.2510).
    The FAA revises proposed Sec.  23.910 to clarify that any failure
resulting in the loss of a single powerplant on an airplane with
multiple powerplants cannot result in the failure of other powerplants
unless those failures cannot be reasonably eliminated, in which case
the hazards must be minimized. So, while Sec.  23.2510 does apply to
all powerplant systems, the FAA notes Sec.  23.2410 includes an
exception to the general requirement of Sec.  23.2510 to account for
certain powerplant failures that may prevent continued safe flight and
landing or for which use of a traditional system safety compliance
approach may not be appropriate. Examples of such failures include
engine rotor non-containment and fire. Therefore, the FAA does not
adopt Textron's recommendation to withdraw proposed Sec.  23.910.
    Garmin commented that proposed Sec.  23.910(b) seemed highly
subjective and recommended eliminating paragraph (b).
    The FAA notes Sec.  23.2410(b) requires consideration of failures
affecting passenger safety such as a fan disconnect on fuselage
embedded engines or exhaust heat exchanger failures that may allow
hazardous fumes to enter the occupant compartment. The FAA finds
withdrawing paragraph (b) would eliminate the requirement for an
applicant to assess potential causes of serious injury to airplane
occupants. Additionally, it serves as the underlying requirement for
the development of a more-detailed means of compliance. Therefore, the
FAA adopts the language in Sec.  23.2410(b) as proposed.
    ANAC observed that there is no requirement in proposed Sec.  23.910
to ensure powerplant-driven components, necessary for airplane
operation, are suitable for installation in airplanes certificated
under part 23, and the powerplant installation requirement in proposed
Sec.  23.900 (now Sec.  23.2400) is related only to components that
affect propulsion safety. ANAC noted the rule does not capture the
design precautions established in the former Sec. Sec.  23.933 and
23.1155. The commenter also asserted that while proposed Sec.  23.910
addresses hazard mitigation in the event of powerplant systems failure,
compliance with proposed Sec.  23.910 for turbine engines would be
directly related to protection against inadvertent thrust reverser
deployment.
    The FAA notes ANAC's concerns; however, as discussed in the
preamble for Sec.  23.2400, the FAA has added paragraph (e) to Sec.
23.2400 to address powerplant component installation. Additionally, the
FAA addresses the design precautions of former Sec. Sec.  23.933 and
23.1155, which provided reversing system requirements for turbojets,
turbofans, and propellers, in the performance-based requirements
contained in Sec.  23.2420, ``Reversing systems'' (proposed as Sec.
23.920).
d. Automatic Power or Thrust Control Systems (Proposed Sec.  23.915/Now
Sec.  23.2405
    In the NPRM, proposed Sec.  23.915 (now Sec.  23.2405) would have
required a power or thrust augmentation system that automatically
controls the power or thrust on the operating powerplant to provide an
indication to the flightcrew when the system is operating, provide a
means for the pilot to deactivate the automatic functions, and prevent
inadvertent deactivation.
    Textron commented the requirements of proposed Sec.  23.915 could
easily be addressed by revising proposed Sec.  23.900 to state that
state an automatic power reserve (APR) system that automatically
advances the power or thrust on the operating engine(s), when any
engine fails during takeoff, must comply with the applicable
requirements of the subpart. Textron noted that this language is
included in Appendix E of the Part 23 ARC Report. Also, Textron
recommended deleting the prescriptive requirement in proposed Sec.
23.915(a) for the system to provide an indication that it is operating,
stating that such a requirement and other high level requirements are
redundant.

    The FAA finds the adoption of the proposed Part 23 ARC language, as
recommended by Textron, would limit the scope of this rule to existing
APR type systems. The FAA also finds the intent of the ARC language is
better captured in this rule, which can apply to a wider range of
potential future automatic power or thrust control systems. The FAA
partially agrees with the commenter's request to remove the requirement
for annunciation from proposed Sec.  23.915(a). Although the proposal
did not specifically state there must be an annunciation of the
system's status, it did require the system to provide an indication of
the status. The proposal has been revised to require a means to
indicate the system is in an operating condition. The FAA finds this
revision will provide applicants with more flexibility in designing a
system to provide the flightcrew with information regarding the
operational status of this critical safety system.
    ANAC stated the proposed requirements of this section are too
prescriptive and the requirements of proposed Sec. Sec.  23.1310,
23.1500, and 23.910, which address system reliability, status
monitoring, flightcrew interface, and warning indications, provide
equivalent requirements that eliminate the need for a specific
regulation to address APR systems.
    The FAA does not find the provisions of proposed Sec.  23.915 are
adequately addressed by the requirements in proposed Sec.  23.900. The
requirements in Sec.  23.2405 (proposed Sec.  23.915) provide
additional specific requirements the FAA considers necessary for the
certification of APR systems in airplanes. The FAA does not find the
requirements of Sec.  23.2400 (proposed Sec.  23.900) alone would
adequately address the requirements necessary for approval of an
automatic power control system. The specific requirements in the rule
for the system to provide indication to the flightcrew that it is
operating are necessary given the critical nature of both existing and
future APR systems that may vary thrust or power to provide airplane
control during the failure of an engine. In response to ANAC's comment
that Sec.  23.915 could be replaced with a more general rule covering
system reliability, crew interface, monitoring, and warning, the FAA
finds attempting to address too many systems under a general system
safety requirement may result in the excessive application of non-
standard performance requirements across the industry. Accordingly, for
systems where basic performance requirements can be established,
without requiring specific knowledge of the system's design, those
requirements will be contained in a specific rule. This concept is
further discussed under Sec.  23.2420.
    EASA suggested the FAA address auto power control systems and
reverser systems (proposed Sec. Sec.  23.915 and 23.920) in a single
requirement that would address other systems such as those that use
asymmetric thrust to provide directional control. EASA recommended
changing the title of the proposed section to ``Propulsion Augmentation
Systems'' to ensure systems that augment propulsion in any direction
(drag, thrust, direction, lift) are addressed.
    The FAA notes the basic performance requirements for automatic
power control systems are different from those required for reverser
systems. Additionally, the FAA also notes adopting the term
``augmentation'' implies that only a system's use of additional thrust
or power would be addressed, whereas systems are envisioned that may
also reduce power on an operating propulsion system or use aerodynamic
means to respond to power or thrust abnormalities. The FAA considers an
automatic power or thrust control system to be a system that
automatically intervenes and provides direct or modified control to
each engine, leaving the pilot indirectly in control or possibly not in
control for an automatic recovery type function. Reversing systems
simply change the direction of thrust or power at the direct control of
the pilot. As these systems are significantly different, the FAA has
determined it is necessary to retain a specific section for both
automatic power or thrust control systems and reversing systems.
    The FAA reviewed the draft language of CS 23.2405, Propulsion
augmentation systems, and found it directly applicable to automatic
power or thrust control systems. Its provisions also address many of
the commenters' concerns, especially with respect to the certification
of airplanes with advanced automatic control systems. This language is
consistent with, but less prescriptive than, the requirements of former
appendix H to part 23. Accordingly, the FAA revises proposed Sec.
23.915 by adopting the language from CS 23.2405(b) through (e) in Sec.
23.2405(a) through (d).
    Textron noted it was unclear if the proposed rule was attempting to
address ``auto throttle'' applications exclusively.
    The FAA did not intend proposed Sec.  23.915 to address
autothrottle or autothrust systems unless the system has the capability
to command a change to power or thrust that is not directly commanded
by movement of the primary power setting control. Such a system might
vary power on multiple powerplants to maintain level flight or add
thrust beyond that commanded by the throttle when an engine failure is
detected.
    Garmin and the Associations suggested eliminating proposed Sec.
23.915(b). Garmin stated that emerging technology may include systems
that have sufficient design integrity and provide enough safety benefit
that permitting deactivation as required by proposed Sec.  23.915(b)
could have the unintended effect of reducing safety. The Associations
noted in the event the automatic power control systems of less
reliability are used, compliance with proposed Sec.  23.910 should
result in designs that achieve the risk mitigations intended by the
requirements of proposed Sec.  23.915(b).
    The FAA agrees that requiring a means for a pilot to deactivate the
automatic function may have an adverse effect on safety. The FAA also
agrees emerging technology may result in the development of a system
with sufficient integrity the flightcrew does not directly control the
thrust of each engine, but rather the power control system takes
commands from the flightcrew and automatically controls each engine to
execute that command, in both normal conditions and in the event of a
failure of an engine. Accordingly, the FAA revises the rule to account
for the possibility of a broader range of automatic power or thrust
control systems and has removed the requirement for pilot deactivation
of the automatic function of these systems where a system failure is
shown to be extremely remote. The type of system that would have this
level of authority is envisioned to be similar to an automated flight
control or fly-by-wire system, and an applicant would be expected to
show the system has sufficient design integrity to meet this standard.
To provide applicants with greater design flexibility, the FAA also
revises the proposal to require the flightcrew to be able to override,
rather than deactivate systems with lower design integrity. It is
intended this requirement will apply to those systems whose failure can
be reasonably detected by the flightcrew and for which overriding the
automatic function would not have an adverse effect on safety. Such a
situation typically exists with traditional automatic power reserve
systems.
    ANAC suggested the requirement to maintain the maximum thrust/power
increment limit be specifically retained in the regulation and not
serve as a possible means of compliance. ANAC

believes that although it is arbitrary, the 10 percent limit for the
APR is considered in the current regulation to be a straightforward and
acceptable decrement from a safety standpoint in limiting both runway
critical takeoffs and degradation of all-engine climb performance
factors that are not addressed by former part 23 Appendix H, paragraphs
H23.4(b) and (c).
    The FAA notes any automatic power or thrust control system will be
required to meet all applicable regulations including Sec.  23.2415,
which requires that failures that would prevent continued safe flight
not result from a single failure or from a likely combination of
failures. In addition, the FAA notes that takeoff performance is
determined considering a critical loss of thrust. Although the 10
percent value referred to by ANAC may be considered an arbitrary limit
on the additional thrust that can be provided by an APR system, the FAA
considers it unlikely an APR design would be proposed that reserves a
significant amount of thrust for use only in the event of an engine
failure during takeoff. Yet given the broader scope of this rule,
limiting automatic power control thrust to 10 percent may not
realistically permit system designs intended to augment lift, control,
or stability through the propulsion system. Therefore, the FAA has
decided not to include the 10 percent limit in the rule.
    Kestrel questioned whether the proposed section would permit
alternate automatic power control systems (such as those without thrust
lever drivers) that could meet the intent of proposed Sec.  23.1500
(now Sec.  23.2600) without an ELOS finding or an issue paper. Kestrel
noted former Sec.  23.779 requires commanded engine thrust and actual
engine thrust agree, which the commenter said has historically been
accomplished by the thrust levers being mechanically driven to the
actual engine thrust position.
    The FAA notes that Sec.  23.2600 does not specifically require a
throttle lever, only powerplant controls. Therefore, if a design were
proposed that allowed a qualified flightcrew member to perform all
tasks associated with the intended powerplant control functions, an
ELOS finding would not likely be required to obtain approval of that
automatic power control system.
    NJASAP supported the language of proposed Sec.  23.915 and noted
automatic power control system technology will be available to more
airplanes in lower certification categories in the not-too-distant
future.
e. Reversing Systems (Proposed Sec.  23.920/Now Sec.  23.2420)
    In the NPRM, proposed Sec.  23.920 (now Sec.  23.2420) would have
required an airplane to be capable of continued safe flight and landing
under any available reversing system setting.
    Textron stated the proposed language is too ``high-level'' and does
not provide adequate performance-based requirements for an applicant to
show compliance with the rule. Textron also stated the rule was ``a bit
severe'' and noted the rule could be interpreted to mean that a single-
or multiengine turboprop may now need a reverser lock out system for
flight. Textron also claimed the flight testing required to demonstrate
compliance with the proposed requirement may be complicated and
dangerous. To address its concerns, Textron recommended using the
language from CS 23.505.
    Air Tractor commented that it seems impossible to expect an
airplane to be capable of safe flight and landing with application of
full reverse thrust. Air Tractor suggested the proposed language
expected the airplane to ``know'' the difference between a pilot
command for reverse thrust when the airplane is on the ground versus
when it is in air, and to overrule the pilot command if the airplane is
still flying. Air Tractor observed that while this might be an easy
control issue when combined with a squat switch, many airplanes with
spring steel fixed landing gear do not have squat switches. Air Tractor
also noted that it has not been a safety issue to have reverse thrust
capability on certain types of single-engine turboprop airplanes, all
of which employ multiple means to prevent inadvertent selection of the
reverse range and warn when that range is selected.
    The Associations noted the proposed rule could be misconstrued to
indicate the FAA will no longer permit throttle gates, which are
traditionally used on turboprop designs. The commenters contended this
would necessitate the development of weight on wheels lockouts and
other complex designs that were not required by the former rule, and
for which there is no measurable safety data to indicate this was an
area of safety concern. The commenters recommended revising the rule to
state the airplane must be capable of safe flight and landing under any
``easily selectable'' reversing system setting, rather than ``any
available'' reversing system setting.
    ICON asked for clarification as to whether proposed Sec.  23.920
was intended to mean that if a reversible pitch setting exists on a
propeller, an airplane must be able to continue flight even with
selection of full reverse pitch. ICON also believed the proposed rule
could be interpreted to require a demonstration of safe flight and
landing at full reverse power.