[Federal Register Volume 61, Number 28 (Friday, February 9, 1996)]
[Rules and Regulations]
[Pages 5138-5151]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-2081]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 23
[Docket No. 27805; Amendment No. 23-48]
RIN 2120-AE62
Airworthiness Standards; Airframe Rules Based on European Joint
Aviation Requirements
AGENCY: Federal Aviation Administration, DOT.
ACTION: Final rule.
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SUMMARY: This final rule amends the airframe airworthiness standards
for normal, utility, acrobatic, and commuter category airplanes. This
amendment completes a portion of the Federal Aviation Administration
(FAA) and the European Joint Aviation Authorities (JAA) effort to
harmonize the Federal Aviation Regulations and the Joint Aviation
Requirements (JAR) for airplanes certificated in these categories. This
amendment will provide nearly uniform airframe airworthiness standards
for airplanes certificated in the United States under 14 CFR part 23
and in the JAA countries under Joint Aviation Requirements 23,
simplifying international airworthiness approval.
EFFECTIVE DATE: March 11, 1996.
FOR FURTHER INFORMATION CONTACT:
Kenneth W. Payauys, ACE-111, Small Airplane Directorate, Aircraft
Certification Service, Federal Aviation Administration, 601 East 12th
Street, Kansas City, Missouri 64106; telephone (816) 426-5688.
SUPPLEMENTARY INFORMATION:
Background
This amendment is based on Notice of Proposed Rulemaking (NPRM) No.
94-20 (59 FR 35196, July 8, 1994). All comments received in response to
Notice 94-20 have been considered in adopting this amendment.
This amendment completes part of an effort to harmonize the
requirements of part 23 and JAR 23. The revisions to part 23 in this
amendment largely pertain to airframe airworthiness standards. Three
other final rules are being issued in this Federal Register that
pertain to airworthiness standards for systems and equipment, flight,
and powerplant. These related rulemakings are also part of the
harmonization effort. Interested persons should review all four final
rules to ensure that all revisions to part 23 are recognized.
The harmonization effort was initiated at a meeting in June 1990 of
the JAA Council (consisting of JAA members from European countries) and
the FAA, during which the FAA Administrator committed the FAA to
support the harmonization of the U.S. regulations with the JAR that
were being developed. In response to the commitment, the FAA Small
Airplane Directorate established an FAA Harmonization Task Force to
work with the JAR 23 Study Group to harmonize part 23 with the proposed
JAR 23. The General Aviation Manufacturers Association (GAMA) also
established a JAR 23/part 23 committee to provide technical assistance.
The FAA, JAA, GAMA, and the Association Europeenne des
Constructeurs de Material Aerospatial (AECMA), an organization of
European airframe manufacturers, met on several occasions in a
continuing harmonization effort.
Near the end of the effort to harmonize the normal, utility, and
acrobatic category airplane airworthiness standards, the JAA requested
and received recommendations from its member countries on proposed
airworthiness standards for commuter category airplanes. Subsequent JAA
and FAA meetings on this issue resulted in proposals that were
reflected in Notice 94-20 to revise portions of the part 23 commuter
category airworthiness standards. Accordingly, this final rule adopts
the airframe airworthiness standards for all part 23 airplanes.
In January 1991, the FAA established the Aviation Rulemaking
Advisory Committee (ARAC) (56 FR 2190, January 22, 1991). At an FAA/JAA
Harmonization Conference in Canada in June 1992, the FAA announced that
it would consolidate the harmonization effort within the ARAC
structure. The FAA assigned to ARAC the rulemakings related to JAR 23/
part 23 harmonization, which ARAC assigned to the JAR/FAR 23
Harmonization Working Group. The proposal for airframe airworthiness
standards contained in Notice No. 94-20 were a result of both the
working group's efforts and the efforts at harmonization that occurred
before the formation of the working group.
The JAA submitted comments to the FAA on January 20, 1994, in
response to the four draft proposals for harmonization of the part 23
airworthiness standards. The JAA submitted comments again during the
comment period of the NPRM. At the
[[Page 5139]]
April 26, 1995, ARAC JAR/FAR 23 Harmonization Working Group meeting,
the JAA noted that many of the comments in the January 20 letter had
been satisfied or were no longer relevant. The few remaining items
concern issues that are considered beyond the scope of this rulemaking
and, therefore, will be dealt with at future FAA/JAA Harmonization
meetings.
Discussion of Comments
General
Interested persons were invited to participate in the development
of these final rules by submitting written data, views, or arguments to
the regulatory docket on or before October 28, 1994. Five commenters
responded to Notice 94-20. Minor technical and editorial changes have
been made to the proposed rules based on relevant comments received,
consultation with the ARAC, and further review by the FAA
Discussion of Amendments
Section 23.301 Loads
The FAA proposed to amend Sec. 23.301(d) by limiting the
applicability of Appendix A to part 23 to ``single-engine, excluding
turbines'' airplanes, rather than the current single-engine limitation.
The effect of the proposed changes would be to eliminate alternative
Appendix A airplane design requirements for turbine engines because the
JAA determined, and the FAA agrees, that only single-engine airplanes,
excluding turbines, were envisioned when Appendix A was introduced.
Turbine airplane designs could continue to be FAA certificated by
substantiation to part 23.
No comments were received on the proposal for this section, and it
is adopted as proposed.
Section 23.335 Design Airspeeds
The FAA proposed to revise portions of Sec. 23.335 for
clarification and harmonization with JAR 23. The FAA proposed to revise
paragraph (a)(1) by adding the phrase ``wing loading at the design
maximum takeoff weight'' as a definition for W/S and by revising
paragraphs (a)(1)(i) and (ii) to correct the equations for design
cruise speed from ``33 W/S'' to ``33 (W/S)'' and from ``36
W/S'' to ``36 (W/S).''
The FAA proposed to revise Sec. 23.335(b)(4) by adding a new
paragraph (b)(4)(iii) that includes a new mach number speed margin,
0.07M, for commuter category airplanes. Because commuter category
airplanes are normally operated at higher altitudes than normal,
utility, and acrobatic category airplanes, they experience greater
atmospheric variations, such as horizontal gusts and the penetration of
jet streams or cold fronts; therefore, a higher minimum speed margin is
required. The JAR proposed adding this mach number speed margin. The
original mach number speed margin of 0.05M would be retained for
normal, utility, and acrobatic category airplanes.
An incorrect equation, ng Vs1, appears in
Sec. 23.335(d)(1). This equation for the design speed for maximum gust
intensity, VB, is corrected to Vs1 (ng).
No comments were received on the proposals for this section, and
they are adopted as proposed.
Section 23.337 Limit Maneuvering Load Factors
The FAA proposed to revise Sec. 23.337(a)(1) by clarifying the
equation and by adding a definition for ``W.'' This definition of
``W,'' ``design maximum takeoff weight,'' was requested by the JAA to
harmonize with JAR 23.
No comments were received on the proposal for this section, and it
is adopted as proposed.
Section 23.341 Gust Load Factors
The FAA proposed to reorganize Sec. 23.341 to provide a new
paragraph (a), that would clarify that each airplane must be designed
to withstand loads of each lifting surface that result from gusts
specified in Sec. 23.333(c). It also proposed to reorganize the section
as follows: (1) Redesignate existing paragraphs (a) and (b) as (b) and
(c), respectively; (2) revise the text of new paragraph (b) to delete
the phrase ``considering the criteria of Sec. 23.333(c), to develop the
gust loading on each lifting surface'' since this requirement would be
located in proposed paragraph (a); and, (3) revise new paragraph (c) to
delete the phrase ``for conventional configurations'' because it is no
longer accurate, and to revise the definition for wing loading (W/S).
No comments were received on the proposals for this section, and
they are adopted as proposed.
Section 23.343 Design Fuel Loads
The FAA proposed a new Sec. 23.343. The proposed requirement would
apply to all part 23 airplane categories, except paragraph (c), which
is limited to commuter category airplanes.
Comment: The JAA states that while the JAR 23 Study Group supports
the technical intent of paragraph (c), since the JAA has no JAR 91
operating rule corresponding to part 91. The JAA must wait for an
operating rule to be developed. The JAA has proposed a Notice of
Proposed Action (NPA) to adopt paragraph (c) in JAR 23 if and when an
operating rule for a 45-minute fuel reserve is created.
FAA Response: The FAA decided to continue with the final rule, as
proposed.
This proposal is adopted as proposed.
Section 23.345 High Lift Devices
To place all ``flap'' requirements in one location, and to
harmonize the requirements with JAR 23, the FAA proposed to revise
Sec. 23.345 as follows: (1) Make minor organizational, and non-
substantive, clarifying changes; (2) Change the term ``fully
deflected'' to ``fully extended'' because it more accurately describes
flap conditions and positions; (3) Remove the phrase ``resulting in
limit load factors'' because the requirement already exists in
Sec. 23.301(a); (4) Redesignate current paragraph (c) as paragraph (d)
and revise it to include the flap requirements of Sec. 23.457; (5)
Redesignate current paragraph (d) as paragraph (c); and (6) Incorporate
the flap requirements of Sec. 23.457 into Sec. 23.345(b) and
Sec. 23.345(d), as redesignated, and delete paragraph (e), which is
redundant.
No comments were received on the proposals for this section, and
they are adopted as proposed.
Section 23.347 Unsymmetrical Flight Conditions
The FAA proposed to revise Sec. 23.347 to redesignate the existing
text as paragraph (a) and to add a new paragraph (b) to include
requirements for a flick maneuver (snap roll), if requested for
acrobatic category airplanes.
No comments were received on the proposal for this section, and it
is adopted as proposed.
Section 23.349 Rolling Conditions
The FAA proposed to revised Sec. 23.349(a)(2) to simplify the
unsymmetric semispan load assumption for normal, utility, and commuter
category airplanes to 100 percent on one wing semispan and 75 percent
on the other wing semispan for all design weights up through 19,000
pounds. The preamble to the NPRM did not include the explanation that
the proposed 100 percent and 75 percent load distribution applied only
to normal, utility, and commuter category airplanes. The NPRM did not
include acrobatic category airplanes in this proposed requirement.
However, the proposed regulatory language for Sec. 23.349(c)(2)
correctly reflects the FAA's intent.
[[Page 5140]]
While preparing the NPRM, the FAA had suggested varying the latter
percentage linearly between 70 percent and 77.5 percent to include
aircraft weighing up to 19,000 pounds. After discussion with the JAA,
the FAA agreed that 75 percent is an appropriate assumption for all
part 23 airplanes except acrobatic category airplanes.
No comments were received on the proposal for this section, and it
is adopted as proposed.
Section 23.369 Rear Lift Truss
The FAA proposed to amend Sec. 23.369 by amending the equation and
by adding a definition for wing loading (W/S) to clarify the rule.
No comments were received on the proposal for this section, and it
is adopted as proposed.
Section 23.371 Gyroscopic and Aerodynamic Loads
The FAA proposed to revise and reorganize Sec. 23.371 by
designating the existing text as paragraph (a) and adding new
paragraphs (b) and (c).
The proposed revisions to the text of proposed paragraph (a) would
delete the limitation for turbine powered engines; add inertial loads;
and replace the word ``engines'' with ``engine(s) and propeller(s), if
applicable.'' The proposed changes clarify that these requirements
apply to all part 23 airplanes.
The FAA proposed a new paragraph (b) to clarify and distinguish the
requirements for airplanes approved for aerobatic maneuvers.
The FAA proposed new paragraph (c) to clarify that commuter
category airplanes must comply with the gust conditions in Sec. 23.341
in addition to the requirement of Sec. 23.371(a).
Comment: The JAA recommended that the words ``In addition,'' which
appear at the beginning of JAR 23.371(b) but not in Sec. 23.371(b),
could result in misreading the requirements for airplanes approved for
aerobatic maneuvers. The JAA's concern is that a reader might think
that the requirements of paragraph (b) for airplanes approved for
aerobatic maneuvers are in place of, rather than in addition to, the
requirements of paragraph (a).
FAA Response: The FAA is aware that the words ``in addition''
appear in the JAR and understands that the JAA believes the words are
necessary to prevent an interpretation that airplanes approved for
aerobatic maneuvers need only comply with the requirements of paragraph
(b).
Under standard rules of regulatory interpretation, it is not
necessary to add the words ``in addition'' since the applicability of
paragraph (a) should be based on its wording and not on the wording of
paragraph (b). However, the FAA concludes that JAA's concern can be
addressed by rewording paragraph (b) and new paragraph (c) to make it
clear that persons subject to those paragraphs must meet both
paragraphs (a) and certain additional requirements. As rewritten,
paragraph (b) states ``For airplanes approved for aerobatic maneuvers,
each engine mount and its supporting structure must meet the
requirements of paragraph (a) of this section and be designed to
withstand the load factors expected during combined maximum yaw and
pitch velocities.'' Paragraph (c) uses parallel language. Paragraph (c)
would apply to aircraft certificated in the commuter category, whereas,
as proposed, paragraph (b) would apply to aircraft ``approved for
aerobatic maneuvers,'' since this approval can be given for aircraft
not certificated in the acrobatic category.
This proposal is adopted with the above changes.
Section 23.391 Control Surface Loads
The FAA proposed to revise Sec. 23.391 by deleting paragraph (b).
Paragraph (b) references Appendix B, which was removed by Amendment No.
23-42 (56 FR 344, January 3, 1991).
No comments were received on the proposal for this section, and it
is adopted as proposed.
Section 23.393 Loads Parallel to Hinge Line
The FAA proposed a new Sec. 23.393. Proposed new Sec. 23.393 would
contain a modified version of the requirement of Sec. 23.657(c)
concerning loads parallel to the hinge line, which were proposed to be
deleted from Sec. 23.657.
No comments were received on the proposal for this section, and it
is adopted as proposed.
Section 23.399 Dual Control System
The FAA proposed to redesignate the text of Sec. 23.399 as
paragraph (a), and to add a new paragraph (b) that addresses the forces
exerted on a dual control system when both pilots act together. This
would clarify that it is the greater of the forces that apply.
No comments were received on the proposal for this section, and it
is adopted as proposed.
Section 23.415 Ground Gust Conditions
The FAA proposed to amend Sec. 23.415 by revising paragraph (a)(2)
to add a definition for wing loading (W/S). The FAA also proposed to
revise paragraph (c), which was added in Amendment No. 23-45 (58 FR
42136, August 6, 1993), to incorporate a more comprehensive tie-down
criteria.
No comments were received on the proposals for this section, and it
is adopted as proposed.
Section 23.441 Maneuvering Loads
The FAA proposed to revise Sec. 23.441(b) to include a new design
requirement for the vertical tail of a commuter category airplane.
Comment: The JAA comments that while the intent of the proposed
requirement is the same as the comparable requirement in JAR 23, the
wording is different. The JAA reported that the FAA proposed final rule
version will be considered for full harmonization by the JAA through
NPA action once the final rule is published.
FAA Response: The proposal is adopted as proposed.
Section 23.443 Gust Loads
The FAA proposed to revise Sec. 23.443(c) by changing the format of
the formula, revising the definition of weight (``W''), and correcting
the subscripts of the distance to the lift center, (``lvt''). The
current definition reads ``W=airplane weight (lbs.).'' The new
definition reads ``W=the applicable weight of the airplane in the
particular load case (lbs.).'' These changes are for clarity.
No comments were received on the proposal for this section, and it
is adopted as proposed.
Sections 23.455 Ailerons
The FAA proposed to amend the heading the precedes Sec. 23.455 by
deleting the term ``Wing Flaps'' so that the heading reads ``AILERONS
AND SPECIAL DEVICES.'' This change would reflect the deletion of the
wing flap requirements from Sec. 23.457 and their placement in
Sec. 23.345.
No comments were received on this proposal, and it is adopted as
proposed.
Section 23.457 Wing Flaps
The FAA proposed to delete this section. As discussed under
Sec. 23.345, above, the wing flap requirements have been revised and
consolidated in Sec. 23.345 to group these requirements together.
No comments were received on the proposal for this section, and it
is adopted as proposed.
Section 23.473 Ground Load Conditions and Assumptions
The FAA proposed to revise Sec. 23.473(c)(1) to change the
incorrect reference to ``Sec. 23.67 (a) or (b)(1)'' to ``Sec. 23.67
(b)(1) or (c).''
[[Page 5141]]
Because the FAA intended that turbine powered airplanes be included
in Sec. 23.473(c)(1), since these airplanes are required to be ``climb
positive'' with one engine inoperative, the FAA proposed that
Sec. 23.473(c)(1) also reference Sec. 23.67(c). The FAA also determined
that to achieve the intent described, Sec. 23.473(c)(1) should also
reference Sec. 23.67 (b)(1) or (c).
The FAA also proposed to revise paragraph (f), which addresses
energy absorption tests, to parallel the language of JAR 23.473(f). No
substantive change from current paragraph (f) was proposed.
No comments were received on the proposals for this section, and
they are adopted as proposed.
Section 23.497 Supplementary Conditions for Tail Wheels
The FAA proposed a new Sec. 23.497(c) to relocate tail wheel,
bumper, or energy absorption device design standards for airplanes with
aft-mounted propellers. These requirements currently exist in
Sec. 23.925(b). They are being moved because the FAA determined that
certain portions of the design standards for these devices more
properly belong in Subpart C--Structure.
No comments were received on the proposal for this section, and it
is adopted as proposed.
Section 23.499 Supplementary Conditions for Nose Wheels
The FAA proposed to add new paragraphs (d) and (e) to Sec. 23.499
to establish nose wheel conditions for airplanes with a steerable nose
wheel controlled by hydraulic or other power and for airplanes with a
steerable wheel that has a direct mechanical connection to the rudder
pedals.
Comment: The JAA comments that the phrase ``has a mechanical
connection to the rudder pedals'' in proposed paragraph (e), absent
appropriate advisory material, could be interpreted to require
different technical solutions than the comparable wording in JAR 23,
``directly connected mechanically to the rudder pedals.''
FAA Response: The FAA agrees that the proposed language in
paragraph (e) requires clarification; in the final rule, the word
``direct'' is inserted before the word ``mechanical''. Also, the last
phrase of paragraph (e) is revised to read ``the mechanism must be
designed to withstand the steering torque for the maximum pilot forces
specified in Sec. 23.397(b).''
This proposal is adopted with the above changes to paragraph (e).
Section 23.521 Water Load Conditions
The FAA proposed to amend Sec. 23.521 by deleting paragraph (c),
which deals with previously approved floats, because the FAA agreed
with the JAA that the requirements of paragraph (c) are covered by the
general requirements of paragraph (a).
No comments were received on the proposal for this section, and it
is adopted as proposed.
Section 23.561 General
The FAA proposed to amend Sec. 23.561 by revising paragraphs (b)
and (d), and adding a new paragraph (e). These changes simplify,
clarify, and ``add references * * * to ensure.'' The FAA proposed to
revise paragraph (b), concerning occupant protection, to make it
correspond to 14 CFR part 25 and JAR 25 that cover large airplanes. The
proposed revision of paragraph (d), concerning turnovers would simplify
and clarify the requirements without making substantive changes. The
FAA proposed a new paragraph (e) to ensure that items of mass that
could injure an occupant are retained by the supporting structure.
No comments were received on the proposals for this section, and
they are adopted as proposed.
Section 23.571 Metallic Pressurized Cabin Structures
The FAA proposed to revise Sec. 23.571 by changing the heading from
``Pressurized cabin'' to ``Metallic pressurized cabin structures''
because nonmetallic structure is addressed in Sec. 23.573(a). The FAA
proposed to revise the introductory text to limit the applicability to
normal, utility, and acrobatic categories because commuter category
airplanes are addressed separately. The FAA proposed to revise
paragraph (a) to require the fatigue strength investigation to show
that the structure can withstand repeated loads of variable magnitude
expected in service.
Comment: The JAA comments that the JAR will be revised to delete
commuter category airplanes from this section. Kal-Aero comments that a
literal interpretation of the proposed changes to Secs. 23.571 and
23.572 ``would require that every subsequent modification to an
aircraft have a fatigue program to substantiate each major repair or
alteration.'' Kal-Aero states that this change is both uneconomical
(Kal-Aero estimates a part 23 fatigue test could cost at least $20
million per certification) and is unnecessary.
FAA Response: The FAA does not agree that the proposed rule
language would require the result suggested by Kal-Aero. The intent is
to provide that there be some test evidence to verify the analysis
validity. The amount of test evidence needed would depend on the
complexity of the design. The FAA points out that this evidence would
be required only when fatigue analysis is used to satisfy the type
certification requirements.
The proposals for this section are adopted as proposed.
Section 23.572 Metallic Wing, Empennage, and Associated Structures
The FAA proposed to revise the section heading to add the word
``metallic,'' to revise paragraph (a) to limit the applicability to
normal, utility, and acrobatic category airplanes, and to make minor
editorial changes. Paragraph (a)(1) would be revised to harmonize with
JAR 23 by requiring tests, or analysis supported by test evidence, as
discussed under Sec. 23.571 of this preamble.
The only comment received on this section is from Kal-Aero, and
applies to this section and to Sec. 23.571. The comment was discussed
under Sec. 23.571.
The proposals are adopted as proposed.
Section 23.573 Damage Tolerance and Fatigue Evaluation of Structure
The FAA proposed to amend Sec. 23.573(a)(5) to make clear that the
limit load capacity of a bonded joint must be substantiated only if the
failure of the bonded joint would result in catastrophic loss of the
airplane.
The FAA proposed to delete Sec. 23.573(c) because its requirements
for inspections and other procedures were proposed to be moved to
Sec. 23.575.
No comments were received on the proposals for this section, and
they are adopted as proposed.
Section 23.574 Metallic Damage Tolerance and Fatigue Evaluation of
Commuter Category Airplanes
The FAA proposed to add a new Sec. 23.574 that addresses damage
tolerance and fatigue evaluation requirements for commuter category
airplanes. As discussed previously, Secs. 23.571 and 23.572 are being
revised to clarify that these sections apply only to normal, utility,
and acrobatic category airplanes. Newly type certificated commuter
category airplanes would have to meet proposed Sec. 23.574 instead of
Secs. 23.571 and 23.572.
The only comment received on this proposed new section is a JAA
statement that this change will be considered for JAR 23. The proposal
is adopted as proposed.
[[Page 5142]]
Section 23.575 Inspections and Other Procedures
The FAA proposed to add a new Sec. 23.575 to clarify that airplane
manufacturers are required to provide recommendations for inspections
frequencies, locations, and methods when a design is approved by the
FAA, and that these items must be included in the Limitations Section
of the Instructions for Continued Airworthiness required by
Sec. 23.1529.
The requirements of Sec. 23.573(c) would be moved to Sec. 23.575
and the requirements are made applicable to Secs. 23.571, 23.572,
23.573 and 23.574.
The only comment on this proposed new section is a JAA statement
that this change will be considered for JAR 23. The proposals are
adopted as proposed.
Section 23.607 Fasteners
The FAA proposed to amend Sec. 23.607 by changing the section
heading, by redesignating the existing text as paragraph (c), and by
adding new paragraphs (a) and (b), as outlined in the NPRM.
Comment: Transport Canada comments that it is possible the language
of proposed paragraph (a) could be interpreted to mean that compliance
is satisfied by the use of a self-locking nut alone in certain
situations, such as when a bolt is not subject to rotation. Transport
Canada suggests adopting the wording of Sec. 27.607, which requires
``two separate locking devices'' when the loss of a removable bolt,
screw, nut, pin or other fastener would jeopardize the safe operation
of the aircraft.
FAA Response: The FAA agrees that the proposed language of
paragraph (a) could be misinterpreted and that the intent of the
section would be clearer if language comparable to Sec. 27.607 is used.
Also, the FAA finds that the section is clearer if it addresses all
removable fasteners without specific mention of bolts, screws, nuts,
pins, etc. Accordingly, paragraph (a) has been revised to read ``Each
removable fastener must incorporate two retaining devices if the loss
of such fastener would preclude continued safe flight and landing'' in
the final rule.
This proposal is adopted with the noted change to paragraph (a).
Section 23.611 Accessibility Provisions
The FAA proposed to amend Sec. 23.611 to require that, for any part
requiring maintenance, such as an inspection or other servicing, there
must be a means of access incorporated into the aircraft design to
allow this servicing to be accomplished. The FAA pointed out in the
NPRM that whether the access provided is appropriate in a particular
case will depend on the nature of the item and the frequency and
complexity of the required inspection or maintenance actions.
The only comment received on this proposed change is a JAA
statement that this change will be considered for the JAR. The proposal
is adopted as proposed.
Section 23.629 Flutter
The FAA proposed to revise Sec. 23.629 to require either flight
flutter tests and rational analysis, or flight flutter tests and
compliance with the FAA's ``Simplified Flutter Prevention Criteria.''
Section 23.629 currently requires flutter substantiation by only one of
three methods: A rational analysis, flight flutter test, or compliance
with the ``Simplified Flutter Prevention Criteria.''
The FAA also proposed to revise paragraph (d)(3)(i) to change the
phrase ``T-tail or boom tail'' to ``T-tail or other unconventional tail
configurations'' to be more inclusive and to represent the standard
used in current certification. The FAA also proposed to harmonize with
JAR 23 by amending paragraphs 23.629 (g) and (h) to remove the ``or
test'' phrase to require that substantiation be done only by analysis.
The FAA proposed a new paragraph (i) that would allow freedom from
flutter to be shown by tests (under paragraph (a)) or by analysis alone
if that analysis is based on previously approved data for an airplane
that has undergone modification that could affect its flutter
characteristics.
No comments were received on the proposals for this section, and
they are adopted as proposed.
Section 23.657 Hinges
The FAA proposed to amend Sec. 23.657 by deleting paragraph (c)
that covers loads parallel to the hinge line because it would be
covered in proposed Sec. 23.393.
No comments were received on the proposal for this section, and it
is adopted as proposed.
Section 23.673 Primary Flight Controls
The FAA proposed to revise Sec. 23.673 to delete the requirements
for two-control airplanes consistent with actions being taken in the
proposed rule on flight requirements for part 23 airplanes (Docket No.
27807, Notice No. 94-22; (59 FR 37878, July 25, 1994)) that affect
Secs. 23.177 and 23.201. The two-control requirements are considered
obsolete. Additionally, harmonization with JAR 23 would be accomplished
by this action.
No comments were received on the proposal for this section, and it
is adopted as proposed.
Section 23.725 Limit Drop Tests
The FAA proposed to amend the effective weight equation in
Sec. 23.725(b) by adding mathematical brackets to the numerator and
parentheses to the denominator to clarify the equation.
No comments were received on the proposal for this section, and it
is adopted as proposed.
Section 23.755 Hulls
The FAA proposed to amend Sec. 23.755 by deleting paragraph (b),
which provides, that hulls of hull seaplanes or amphibians of less than
1,500 pounds need not be compartmented, because paragraph (b) is
redundant. The applicable requirements are contained in paragraph (a).
The FAA also proposed to redesignate paragraph (c) as new paragraph (b)
and to edit it for clarification.
No comments were received on the proposals for this section, and
they are adopted as proposed.
Section 23.865 Fire Protection of Flight Controls, Engine Mounts, and
Other Flight Structures
The FAA proposed to revise Sec. 23.865 by changing the words
``engine compartment'' to ``designated fire zones'' for consistency
with recent revisions to Secs. 23.1203 and 23.1181. The proposed
revision would also add the phrase ``adjacent areas that would be
subjected to the effects of fire in the designated fire zones.''
Comment: The JAA agrees that the technical intent of proposed
Sec. 23.865 is similar to the JAR 23 requirement. Changes to JAR 23 to
adopt the terms proposed in this part 23 section are being considered
by the JAA.
FAA Response: No substantive comment was received, and the
proposals are adopted as proposed.
Section 23.925 Propeller Clearance
The FAA proposed to amend Sec. 23.925(b), Aft mounted propellers,
by removing the requirements on tail wheels, bumpers, and energy
absorption devices and moving them to Sec. 23.497, Supplementary
conditions for tail wheels, as discussed as discussed above. The FAA
also proposed to delete the inspection and replacement criteria for
tail wheel, bumper, and energy absorption devices because the
inspection and replacement requirements are stated in Sec. 23.1529.
No comments were received on the proposals for this section, and
they are adopted as proposed.
[[Page 5143]]
Appendix A
The FAA proposed to revise three areas of Appendix A: (1) A23.1
General; (2) A23.11 Control surface loads, paragraph (c), Surface
loading conditions; and (3) Table 2--Average limit control surface
loading. The FAA proposed to add a new figure to Appendix A: Figure A7,
Chordwise load distribution for stabilizer and elevator, or fin and
rudder. The revisions specify the configurations for which the wing and
tail surface loads, required by A23.7, are valid. The FAA discovered a
need for a clarification change in paragraph A23.a(a)(1) during the
post comment review period. The words ``excluding turbine powerplants''
are clearer than the words ``excluding turbines.'' This revision is
included in the final rule to more clearly convey the intended meaning.
No comments were received on the proposals for Appendix A, and they
are adopted with the change explained above.
Final Regulatory Evaluation, Final Regulatory Flexibility
Determination, and Trade Impact Assessment
Changes to Federal regulations must undergo several economic
analyses. First, Executive Order 12866 directs Federal agencies to
promulgate new regulations only if the potential benefits to society
justify its costs. Second, the Regulatory Flexibility Act of 1980
requires agencies to analyze the economic impact of regulatory changes
on small entities. Finally, the Office of Management and Budget directs
agencies to assess the effects of regulatory changes on international
trade. In conducting these assessments, the FAA has determined that
this rule: (1) Will generate benefits exceeding its costs and is
``significant'' as defined in the Executive Order; (2) is
``significant'' as defined in DOT's Policies and Procedures; (3) will
not have a significant impact on a substantial number of small
entities; and (4) will not constitute a barrier to international trade.
These analyses, available in the docket, are summarized below.
Comments Related to the Economics of the Proposed Rule
Two comments were received regarding the economic impact of the
proposals; one concerning Sec. 23.571, Metallic pressurized cabin
structures, and one concerning Sec. 23.572, Metallic wing, empennage,
and associated structures. Both of these comments, as well as the FAA's
responses, are included in the section ``Discussion of Amendments.''
Regulatory Evaluation Summary
The FAA has identified 6 sections that will result in additional
compliance costs, totalling between $10,000 and $17,000 per
certification. When amortized over a production run, these costs will
have a negligible impact on airplane price, less than $100 per
airplane.
The primary benefit of the rule will be the cost efficiencies of
harmonization with the JAR for those manufacturers that market
airplanes in JAA countries as well as to manufacturers in JAA countries
that market airplanes in the United States. Other benefits of the rule
will be decreased reliance on special conditions, simplification of the
certification process through clarification of existing requirements,
and increased flexibility through optional designs.
Regulatory Flexibility Determination
The Regulatory Flexibility Act of 1980 (RFA) was enacted by
Congress to ensure that small entities are not unnecessarily and
disproportionately burdened by Federal regulations. The RFA requires a
Regulatory Flexibility Analysis if a rule will have a significant
economic impact, either detrimental or beneficial, on a substantial
number of small entities. Based on FAA Order 2100.14A, Regulatory
Flexibility Criteria and Guidance, the FAA has determined that the rule
will not have a significant economic impact on a substantial number of
small entities.
International Trade Impact Assessment
The rule will not constitute a barrier to international trade,
including the export of U.S. goods and services to foreign countries
and the import of foreign goods and services into the United States.
Instead, the airframe certification procedures have been harmonized
with those of the JAA and will lessen restraints on trade.
Federalism Implications
The regulations herein would not have substantial direct effects on
the States, on the relationship between the national government and the
States, or on the distribution of power and responsibilities among the
various levels of government. Therefore, in accordance with Executive
Order 12612, it is determined that this rule does not have sufficient
federalism implications to warrant the preparation of a Federalism
Assessment.
Conclusion
The FAA is revising the airframe airworthiness standards for
normal, utility, acrobatic, and commuter category airplanes to
harmonize them with the standards that were published for the same
categories of airplanes by the Joint Airworthiness Authorities in
Europe. The revisions reduce the regulatory burden on United States and
European airplane manufacturers by relieving them of the need to show
compliance with different standards each time they seek certification
approval of an airplane in the United States or in a country that is a
member of the JAA.
For the reasons discussed in the preamble, and based on the
findings in the Regulatory Evaluation, the FAA has determined that this
rule is not significant under Executive Order 12866. In addition, the
FAA certifies that this rule will not have a significant economic
impact on a substantial number of small entities under the criteria of
the Regulatory Flexibility Act. This rule is considered not significant
under DOT Regulatory Policies and Procedures (44 FR 11034, February 26,
1979). A regulatory evaluation of the rule has been placed in the
docket. A copy may be obtained by contacting the person identified
under FOR FURTHER INFORMATION CONTACT.
List of Subjects in 14 CFR Part 23
Aircraft, Aviation safety, Signs and symbols.
The Amendments
In consideration of the foregoing, the Federal Aviation
Administration amends 14 CFR part 23 as follows:
PART 23--AIRWORTHINESS STANDARDS: NORMAL, UTILITY, ACROBATIC, AND
COMMUTER CATEGORY AIRPLANES
1. The authority citation for part 23 continues to read as follows:
Authority: 49 U.S.C. 106(g), 40013, 44701, 44702, 44704.
2. Section 23.301(d) is revised to read as follows:
Sec. 23.301 Loads.
* * * * *
(d) Simplified structural design criteria may be used if they
result in design loads not less than those prescribed in Secs. 23.331
through 23.521. For airplane configurations described in appendix A,
Sec. 23.1, the design criteria of appendix A of this part are an
approved equivalent of Secs. 23.321 through 23.459. If appendix A of
this part is used, the entire appendix must be substituted for the
corresponding sections of this part.
3. Section 23.335 is amended by revising paragraph (a)(1); by
removing the period and adding ``; and either--''
[[Page 5144]]
to the end of paragraph (b)(4)(i); by revising paragraph (b)(4)(ii); by
adding a new paragraph (b)(4)(iii); and by revising the introductory
text of paragraph (d)(1) to read as follows:
Sec. 23.335 Design airspeeds.
* * * * *
(a) * * *
(1) Where W/S'=wing loading at the design maximum takeoff weight,
Vc (in knots) may not be less than--
(i) 33 (W/S) (for normal, utility, and commuter category
airplanes);
(ii) 36 (W/S) (for acrobatic category airplanes).
* * * * *
(b) * * *
(4) * * *
(ii) Mach 0.05 for normal, utility, and acrobatic category
airplanes (at altitudes where MD is established); or
(iii) Mach 0.07 for commuter category airplanes (at altitudes where
MD is established) unless a rational analysis, including the
effects of automatic systems, is used to determine a lower margin. If a
rational analysis is used, the minimum speed margin must be enough to
provide for atmospheric variations (such as horizontal gusts), and the
penetration of jet streams or cold fronts), instrument errors, airframe
production variations, and must not be less than Mach 0.05.
* * * * *
(d) * * *
(1) VB may not be less than the speed determined by the
intersection of the line representing the maximum positive lift,
CN MAX, and the line representing the rough air gust velocity on
the gust V-n diagram, or VS1 ng, whichever is less,
where:
* * * * *
4. Section 23.337(a)(1) is revised to read as follows:
Sec. 23.337 Limit maneuvering load factors.
(a) * * *
(1) 2.1+(24,000(W+10,000)) for normal and commuter category
airplanes, where W=design maximum takeoff weight, except that n need
not be more than 3.8;
* * * * *
5. Section 23.341 is amended by redesignating existing paragraphs
(a) and (b) as paragraphs (b) and (c), respectively; by adding a new
paragraph (a); by revising the redesignated paragraph (b); and by
revising the introductory text, the formula, and the definition of ``W/
S'' in the redesignated paragraph (c) to read as follows:
Sec. 23.341 Gust loads factors.
(a) Each airplane must be designed to withstand loads on each
lifting surface resulting from gusts specified in Sec. 23.333(c).
(b) The gust load for a canard or tandem wing configuration must be
computed using a rational analysis, or may be computed in accordance
with paragraph (c) of this section, provided that the resulting net
loads are shown to be conservative with respect to the gust criteria of
Sec. 23.333(c).
(c) In the absence of a more rational analysis, the gust load
factors must be computed as follows--
[GRAPHIC] [TIFF OMMITTED] TR09FE96.010
* * * * *
W/S=Wing loading (p.s.f.) due to the applicable weight of the airplane
in the particular load case.
* * * * *
6. A new Sec. 23.343 is added to read as follows:
Sec. 23.343 Design fuel loads.
(a) The disposable load combinations must include each fuel load in
the range from zero fuel to the selected maximum fuel load.
(b) If fuel is carried in the wings, the maximum allowable weight
of the airplane without any fuel in the wing tank(s) must be
established as ``maximum zero wing fuel weight,'' if it is less than
the maximum weight.
(c) For commuter category airplanes, a structural reserve fuel
condition, not exceeding fuel necessary for 45 minutes of operation at
maximum continuous power, may be selected. If a structural reserve fuel
condition is selected, it must be used as the minimum fuel weight
condition for showing compliance with the flight load requirements
prescribed in this part and--
(1) The structure must be designed to withstand a condition of zero
fuel in the wing at limit loads corresponding to:
(i) Ninety percent of the maneuvering load factors defined in
Sec. 23.337, and
(ii) Gust velocities equal to 85 percent of the values prescribed
in Sec. 23.333(c).
(2) The fatigue evaluation of the structure must account for any
increase in operating stresses resulting from the design condition of
paragraph (c)(1) of this section.
(3) The flutter, deformation, and vibration requirements must also
be met with zero fuel in the wings.
7. Section 23.345 is revised to read as follows:
Sec. 23.345 High lift devices.
(a) If flaps or similar high lift devices are to be used for
takeoff, approach or landing, the airplane, with the flaps fully
extended at VF, is assumed to be subjected to symmetrical
maneuvers and gusts within the range determined by--
(1) Maneuvering, to a positive limit load factor of 2.0; and
(2) Positive and negative gust of 25 feet per second acting normal
to the flight path in level flight.
(b) VF must be assumed to be not less than 1.4 VS or 1.8
VSF, whichever is greater, where--
(1) VS is the computed stalling speed with flaps retracted at
the design weight; and
(2) VSF is the computed stalling speed with flaps fully
extended at the design weight.
(3) If an automatic flap load limiting device is used, the airplane
may be designed for the critical combinations of airspeed and flap
position allowed by that device.
(c) In determining external loads on the airplane as a whole,
thrust, slipstream, and pitching acceleration may be assumed to be
zero.
(d) The flaps, their operating mechanism, and their supporting
structures, must be designed to withstand the conditions prescribed in
paragraph (a) of this section. In addition, with the flaps fully
extended at VF, the following conditions, taken separately, must
be accounted for:
(1) A head-on gust having a velocity of 25 feet per second (EAS),
combined with propeller slipstream corresponding to 75 percent of
maximum continuous power; and
(2) The effects of propeller slipstream corresponding to maximum
takeoff power.
8. Section 23.347 is amended by designating the existing text as
paragraph (a) and by adding a new paragraph (b) to read as follows:
Sec. 23.347 Unsymmetrical flight conditions.
* * * * *
(b) Acrobatic category airplanes certified for flick maneuvers
(snap roll) must be designed for additional asymmetric loads acting on
the wing and the horizontal tail.
9. Section 23.349(a)(2) is revised to read as follows:
Sec. 23.349 Rolling conditions.
* * * * *
(a) * * *
(2) For normal, utility, and commuter categories, in Condition A,
assume that 100 percent of the semispan wing airload acts on one side
of the airplane and 75 percent of this load acts on the other side.
* * * * *
10. Section 23.369(a) is revised to read as follows:
[[Page 5145]]
Sec. 23.369 Rear lift truss.
(a) If a rear lift truss is used, it must be designed to withstand
conditions of reversed airflow at a design speed of--
V = 8.7 (W/S) + 8.7 (knots), where W/S = wing loading at
design maximum takeoff weight.
* * * * *
11. Section 23.371 is revised to read as follows:
Sec. 23.371 Gyroscopic and aerodynamic loads.
(a) Each engine mount and its supporting structure must be designed
for the gyroscopic, inertial, and aerodynamic loads that result, with
the engine(s) and propeller(s), if applicable, at maximum continuous
r.p.m., under either:
(1) The conditions prescribed in Sec. 23.351 and Sec. 23.423; or
(2) All possible combinations of the following--
(i) A yaw velocity of 2.5 radians per second;
(ii) A pitch velocity of 1.0 radian per second;
(iii) A normal load factor of 2.5; and
(iv) Maximum continuous thrust.
(b) For airplanes approved for aerobatic maneuvers, each engine
mount and its supporting structure must meet the requirements of
paragraph (a) of this section and be designed to withstand the load
factors expected during combined maximum yaw and pitch velocities.
(c) For airplanes certificated in the commuter category, each
engine mount and its supporting structure must meet the requirements of
paragraph (a) of this section and the gust conditions specified in
Sec. 23.341 of this part.
Sec. 23.391 [Amended]
12. Section 23.391 is amended by removing paragraph (b) and
removing the designation of ``(a)'' from the remaining text.
13. A new Sec. 23.393 is added to read as follows:
Sec. 23.393 Loads parallel to hinge line.
(a) Control surfaces and supporting hinge brackets must be designed
to withstand inertial loads acting parallel to the hinge line.
(b) In the absence of more rational data, the inertial loads may be
assumed to be equal to KW, where--
(1) K = 24 for vertical surfaces;
(2) K = 12 for horizontal surfaces; and
(3) W = weight of the movable surfaces.
14. Section 23.399 is revised to read as follows:
Sec. 23.399 Dual control system.
(a) Each dual control system must be designed to withstand the
force of the pilots operating in opposition, using individual pilot
forces not less than the greater of--
(1) 0.75 times those obtained under Sec. 23.395; or
(2) The minimum forces specified in Sec. 23.397(b).
(b) Each dual control system must be designed to withstand the
force of the pilots applied together, in the same direction, using
individual pilot forces not less than 0.75 times those obtained under
Sec. 23.395.
15. Section 23.415 is amended by revising paragraphs (a)(2) and (c)
to read as follows:
Sec. 23.415 Ground gust conditions.
(a) * * *
(2) If pilot forces less than the minimums specified in
Sec. 23.397(b) are used for design, the effects of surface loads due to
ground gusts and taxiing downwind must be investigated for the entire
control system according to the formula:
H = K c S q
where--
H = limit hinge moment (ft.-lbs.);
c = mean chord of the control surface aft of the hinge line (ft.);
S = area of control surface aft of the hinge line (sq. ft.);
q = dynamic pressure (p.s.f.) based on a design speed not less than
14.6 (W/S) + 14.6 (f.p.s.) where W/S = wing loading at design
maximum weight, except that the design speed need not exceed 88
(f.p.s.);
K = limit hinge moment factor for ground gusts derived in paragraph (b)
of this section. (For ailerons and elevators, a positive value of K
indicates a moment tending to depress the surface and a negative value
of K indicates a moment tending to raise the surface).
* * * * *
(c) At all weights between the empty weight and the maximum weight
declared for tie-down stated in the appropriate manual, any declared
tie-down points and surrounding structure, control system, surfaces and
associated gust locks, must be designed to withstand the limit load
conditions that exist when the airplane is tied down and that result
from wind speeds of up to 65 knots horizontally from any direction.
16. Section 23.441 is amended by revising paragraph (a)(2) and
adding a new paragraph (b) to read as follows.
Sec. 23.441 Maneuvering loads.
(a) * * *
(2) With the rudder deflected as specified in paragraph (a)(1) of
this section, it is assumed that the airplane yaws to the overswing
sideslip angle. In lieu of a rational analysis, an overswing angle
equal to 1.5 times the static sideslip angle of paragraph (a)(3) of
this section may be assumed.
* * * * *
(b) For commuter category airplanes, the loads imposed by the
following additional maneuver must be substantiated at speeds from
VA to VD/MD. When computing the tail loads--
(1) The airplane must be yawed to the largest attainable steady
state sideslip angle, with the rudder at maximum deflection caused by
any one of the following:
(i) Control surface stops;
(ii) Maximum available booster effort;
(iii) Maximum pilot rudder force as shown below:
BILLING CODE 4910-13-M
[[Page 5146]]
[GRAPHIC] [TIFF OMMITTED] TR09FE96.006
BILLING CODE 4910-13-C
[[Page 5147]]
(2) The rudder must be suddenly displaced from the maximum
deflection to the neutral position.
* * * * *
17. Section 23.443(c) is revised to read as follows:
Sec. 23.443 Gust loads.
* * * * *
(c) In the absence of a more rational analysis, the gust load must
be computed as follows:
[GRAPHIC] [TIFF OMMITTED] TR09FE96.000
Where--
Lvt=Vertical surface loads (lbs.);
[GRAPHIC] [TIFF OMMITTED] TR09FE96.001
[GRAPHIC] [TIFF OMMITTED] TR09FE96.002
Ude=Derived gust velocity (f.p.s.);
=Air density (slugs/cu.ft.);
W=the applicable weight of the airplane in the particular load case
(lbs.);
Svt=Area of vertical surface (ft.2);
ct=Mean geometric chord of vertical surface (ft.);
avt=Lift curve slope of vertical surface (per radian);
K=Radius of gyration in yaw (ft.);
lvt=Distance from airplane c.g. to lift center of vertical surface
(ft.);
g=Acceleration due to gravity (ft./sec.2); and
V=Equivalent airspeed (knots).
18. The center heading ``AILERONS, WING FLAPS, AND SPECIAL
DEVICES'' that appears between Secs. 23.445 and 23.455 is revised to
read ``Ailerons and Special Devices''.
Sec. 23.457 [Removed]
19. Section 23.457 is removed.
20. Section 23.473 is amended by revising paragraphs (c)(1) and (f)
to read as follows:
Sec. 23.473 Ground load conditions and assumptions.
* * * * *
(c) * * *
(1) The airplane meets the one-engine-inoperative climb
requirements of Sec. 23.67(b)(1) or (c); and
* * * * *
(f) If energy absorption tests are made to determine the limit load
factor corresponding to the required limit descent velocities, these
tests must be made under Sec. 23.723(a).
* * * * *
21. Section 23.497 is amended by adding a new paragraph (c) to read
as follows:
Sec. 23.497 Supplementary conditions for tail wheels.
* * * * *
(c) If a tail wheel, bumper, or an energy absorption device is
provided to show compliance with Sec. 23.925(b), the following apply:
(1) Suitable design loads must be established for the tail wheel,
bumper, or energy absorption device; and
(2) The supporting structure of the tail wheel, bumper, or energy
absorption device must be designed to withstand the loads established
in paragraph (c)(1) of this section.
22. Section 23.499 is amended by adding new paragraphs (d) and (e)
to read as follows:
Sec. 23.499 Supplementary conditions for nose wheels.
* * * * *
(d) For airplanes with a steerable nose wheel that is controlled by
hydraulic or other power, at design takeoff weight with the nose wheel
in any steerable position, the application of 1.33 times the full
steering torque combined with a vertical reaction equal to 1.33 times
the maximum static reaction on the nose gear must be assumed. However,
if a torque limiting device is installed, the steering torque can be
reduced to the maximum value allowed by that device.
(e) For airplanes with a steerable nose wheel that has a direct
mechanical connection to the rudder pedals, the mechanism must be
designed to withstand the steering torque for the maximum pilot forces
specified in Sec. 23.397(b).
Sec. 23.521 [Amended]
23. Section 23.521 is amended by removing paragraph (c).
24. Section 23.561 is amended by revising paragraph (b)
introductory text; by revising paragraphs (d)(1); and by adding a new
paragraph (e) to read as follows:
Sec. 23.561 General.
* * * * *
(b) The structure must be designed to give each occupant every
reasonable chance of escaping serious injury when--
* * * * *
(d) * * *
(1) * * *
(i) The most adverse combination of weight and center of gravity
position;
(ii) Longitudinal load factor of 9.0g;
(iii) Vertical load factor of 1.0g; and
(iv) For airplanes with tricycle landing gear, the nose wheel strut
failed with the nose contacting the ground.
* * * * *
(e) Except as provided in Sec. 23.787(c), the supporting structure
must be designed to restrain, under loads up to those specified in
paragraph (b)(3) of this section, each item of mass that could injure
an occupant if it came loose in a minor crash landing.
25. Section 23.571 is amended by revising the heading, the
introductory text, and paragraph (a), to read as follows:
Sec. 23.571 Metallic pressurized cabin structures.
For normal, utility, and acrobatic category airplanes, the
strength, detail design, and fabrication of the metallic structure of
the pressure cabin must be evaluated under one of the following:
(a) A fatigue strength investigation in which the structure is
shown by tests, or by analysis supported by test evidence, to be able
to withstand the repeated loads of variable magnitude expected in
service; or
* * * * *
26. Section 23.572 is amended by revising the heading; by revising
paragraph (a) introductory text; and by revising paragraph (a)(1) to
read as follows:
Sec. 23.572 Metallic wing, empennage, and associated structures.
(a) For normal, utility, and acrobatic category airplanes, the
strength, detail design, and fabrication of those parts of the airframe
structure whose failure would be catastrophic must be evaluated under
one of the following unless it is shown that the structure, operating
stress level, materials and expected uses are comparable, from a
fatigue standpoint, to a similar design that has had extensive
satisfactory service experience:
(1) A fatigue strength investigation in which the structure is
shown by tests, or by analysis supported by test evidence, to be able
to withstand the repeated loads of variable magnitude expected in
service; or
* * * * *
27. Section 23.573 is amended by removing the reference in
paragraph (b) ``Sec. 23.571(c)'' and adding the reference
``Sec. 23.571(a)(3)'' in its place; by removing paragraph (c); and by
revising the introductory text of paragraph (a)(5) to read as follows:
Sec. 23.573 Damage tolerance and fatigue evaluation of structure.
(a) * * *
[[Page 5148]]
(5) For any bonded joint, the failure of which would result in
catastrophic loss of the airplane, the limit load capacity must be
substantiated by one of the following methods--
* * * * *
28. A new Sec. 23.574 is added to read as follows:
Sec. 23.574 Metallic damage tolerance and fatigue evaluation of
commuter category airplanes.
For commuter category airplanes--
(a) Metallic damage tolerance. An evaluation of the strength,
detail design, and fabrication must show that catastrophic failure due
to fatigue, corrosion, defects, or damage will be avoided throughout
the operational life of the airplane. This evaluation must be conducted
in accordance with the provisions of Sec. 23.573, except as specified
in paragraph (b) of this section, for each part of the structure that
could contribute to a catastrophic failure.
(b) Fatigue (safe-life) evaluation. Compliance with the damage
tolerance requirements of paragraph (a) of this section is not required
if the applicant establishes that the application of those requirements
is impractical for a particular structure. This structure must be
shown, by analysis supported by test evidence, to be able to withstand
the repeated loads of variable magnitude expected during its service
life without detectable cracks. Appropriate safe-life scatter factors
must be applied.
29. A new Sec. 23.575 is added to read as follows:
Sec. 23.575 Inspections and other procedures.
Each inspection or other procedure, based on an evaluation required
by Secs. 23.571, 23.572, 23.573 or 23.574, must be established to
prevent catastrophic failure and must be included in the Limitations
Section of the Instructions for Continued Airworthiness required by
Sec. 23.1529.
30. Section 23.607 is revised to read as follows:
Sec. 23.607 Fasteners.
(a) Each removable fastener must incorporate two retaining devices
if the loss of such fastener would preclude continued safe flight and
landing.
(b) Fasteners and their locking devices must not be adversely
affected by the environmental conditions associated with the particular
installation.
(c) No self-locking nut may be used on any bolt subject to rotation
in operation unless a non-friction locking device is used in addition
to the self-locking device.
31. Section 23.611 is revised to read as follows:
Sec. 23.611 Accessibility provisions.
For each part that requires maintenance, inspection, or other
servicing, appropriate means must be incorporated into the aircraft
design to allow such servicing to be accomplished.
32. Section 23.629 is amended by revising the introductory text of
paragraph (a); by redesignating existing paragraphs (b) and (c) as
paragraphs (c) and (b); by revising the introductory text of newly
redesignated (b); by revising newly redesignated paragraph (c); by
revising paragraph (d)(3)(i); by revising paragraphs (g) and (h); and
by adding a new paragraph (i) to read as follows:
Sec. 23.629 Flutter.
(a) It must be shown by the methods of paragraph (b) and either
paragraph (c) or (d) of this section, that the airplane is free from
flutter, control reversal, and divergence for any condition of
operation within the limit V-n envelope and at all speeds up to the
speed specified for the selected method. In addition--
* * * * *
(b) Flight flutter tests must be made to show that the airplane is
free from flutter, control reversal and divergence and to show that--
* * * * *
(c) Any rational analysis used to predict freedom from flutter,
control reversal and divergence must cover all speeds up to 1.2
VD.
(d) * * *
(3) * * *
(i) Does not have a T-tail or other unconventional tail
configurations;
* * * * *
(g) For airplanes showing compliance with the fail-safe criteria of
Secs. 23.571 and 23.572, the airplane must be shown by analysis to be
free from flutter up to VD/MD after fatigue failure, or
obvious partial failure, of a principal structural element.
(h) For airplanes showing compliance with the damage tolerance
criteria of Sec. 23.573, the airplane must be shown by analysis to be
free from flutter up to VD/MD with the extent of damage for
which residual strength is demonstrated.
(i) For modifications to the type design that could affect the
flutter characteristics, compliance with paragraph (a) of this section
must be shown, except that analysis based on previously approved data
may be used alone to show freedom from flutter, control reversal and
divergence, for all speeds up to the speed specified for the selected
method.
Sec. 23.657 [Amended]
33. Section 23.657 is amended by removing paragraph (c).
Sec. 23.673 [Amended]
34. Section 23.673 is amended by removing paragraph (b) and the
paragraph designation ``(a)'' for the remaining paragraph.
35. Section 23.725 is amended by revising the equation in paragraph
(b) to read as follows:
Sec. 23.725 Limit drop tests.
* * * * *
(b) * * *
[GRAPHIC] [TIFF OMMITTED] TR09FE96.003
* * * * *
36. Section 23.755 is amended by removing paragraph (b), and by
redesignating paragraph (c) as paragraph (b) and revising it to read as
follows:
Sec. 23.755 Hulls.
* * * * *
(b) Watertight doors in bulkheads may be used for communication
between compartments.
37. Section 23.865 is revised to read as follows:
Sec. 23.865 Fire protection of flight controls, engine mounts, and
other flight structure.
Flight controls, engine mounts, and other flight structure located
in designated fire zones, or in adjacent areas that would be subjected
to the effects of fire in the designated fire zones, must be
constructed of fireproof material or be shielded so that they are
capable of withstanding the effects of a fire. Engine vibration
isolators must incorporate suitable features to ensure that the engine
is retained if the non-fireproof portions of the isolators deteriorate
from the effects of a fire.
38. Section 23.925 is amended by revising paragraph (b) to read as
follows:
Sec. 23.925 Propeller clearance.
* * * * *
(b) Aft-mounted propellers. In addition to the clearances specified
in paragraph (a) of this section, an airplane with an aft mounted
propeller must be designed such that the propeller will not contact the
runway surface when the airplane is in the maximum pitch attitude
attainable during normal takeoffs and landings.
* * * * *
39. Appendix A is amended by revising the heading, section A23.1,
paragraphs A23.11 (c)(1) and (d), and Table 2; and by adding a new
Figure A7 to the end of the Appendix to read as follows:
[[Page 5149]]
Appendix A to Part 23 Simplified Design Load Criteria
A23.1 General.
(a) The design load criteria in this appendix are an approved
equivalent of those in Secs. 23.321 through 23.459 of this
subchapter for an airplane having a maximum weight of 6,000 pounds
or less and the following configuration:
(1) A single engine excluding turbine powerplants;
(2) A main wing located closer to the airplane's center of
gravity than to the aft, fuselage-mounted, empennage;
(3) A main wing that contains a quarter-chord sweep angle of not
more than 15 degrees fore or aft;
(4) A main wing that is equipped with trailing-edge controls
(ailerons or flaps, or both);
(5) A main wing aspect ratio not greater than 7;
(6) A horizontal tail aspect ratio not greater than 4;
(7) A horizontal tail volume coefficient not less than 0.34;
(8) A vertical tail aspect ratio not greater than 2;
(9) A vertical tail platform area not greater than 10 percent of
the wing platform area; and
(10) Symmetrical airfoils must be used in both the horizontal
and vertical tail designs.
(b) Appendix A criteria may not be used on any airplane
configuration that contains any of the following design features:
(1) Canard, tandem-wing, close-coupled, or tailless arrangements
of the lifting surfaces;
(2) Biplane or multiplane wing arrangements;
(3) T-tail, V-tail, or cruciform-tail (+) arrangements;
(4) Highly-swept wing platform (more than 15-degrees of sweep at
the quarter-chord), delta planforms, or slatted lifting surfaces; or
(5) Winglets or other wing tip devices, or outboard fins.
* * * * *
A23.11 Control surface loads.
* * * * *
(c) * * *
(1) Simplified limit surface loadings for the horizontal tail,
vertical tail, aileron, wing flaps, and trim tabs are specified in
figures 5 and 6 of this appendix.
(i) The distribution of load along the span of the surface,
irrespective of the chordwise load distribution, must be assumed
proportional to the total chord, except on horn balance surfaces.
(ii) The load on the stabilizer and elevator, and the load on
fin and rudder, must be distributed chordwise as shown in figure 7
of this appendix.
(iii) In order to ensure adequate torsional strength and to
account for maneuvers and gusts, the most severe loads must be
considered in association with every center of pressure position
between the leading edge and the half chord of the mean chord of the
surface (stabilizer and elevator, or fin and rudder).
(iv) To ensure adequate strength under high leading edge loads,
the most severe stabilizer and fin loads must be further considered
as being increased by 50 percent over the leading 10 percent of the
chord with the loads aft of this appropriately decreased to retain
the same total load.
(v) The most severe elevator and rudder loads should be further
considered as being distributed parabolically from three times the
mean loading of the surface (stabilizer and elevator, or fin and
rudder) at the leading edge of the elevator and rudder,
respectively, to zero at the trailing edge according to the
equation:
[GRAPHIC] [TIFF OMMITTED] TR09FE96.004
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[GRAPHIC] [TIFF OMMITTED] TR09FE96.007
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Where--
P(x)=local pressure at the chordwise stations x,
c=chord length of the tail surface,
cf=chord length of the elevator and rudder respectively, and
w=average surface loading as specified in Figure A5.
* * * * *
(vi) The chordwise loading distribution for ailerons, wing
flaps, and trim tabs are specified in Table 2 of this appendix.
(d) Outboard fins. Outboard fins must meet the requirements of
Sec. 23.445.
* * * * *
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[GRAPHIC] [TIFF OMMITTED] TR09FE96.008
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* * * * *
Figure A7.--Chordwise Load Distribution for Stabilizer and Elevator or
Fin and Rudder
[GRAPHIC] [TIFF OMMITTED] TR09FE96.009
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[GRAPHIC] [TIFF OMMITTED] TR09FE96.005
where:
w=average surface loading (as specified in figure A.5)
E=ratio of elevator (or rudder) chord to total stabilizer and
elevator (or fin and rudder) chord.
d'=ratio of distance of center of pressure of a unit spanwise length
of combined stabilizer and elevator (or fin and rudder) measured
from stabilizer (or fin) leading edge to the local chord. Sign
convention is positive when center of pressure is behind leading
edge.
c=local chord.
Note: Positive values of w, P1 and P2 are all measured
in the same direction.
Issued in Washington, DC, on January 29, 1996.
David R. Hinson,
Administrator.
[FR Doc. 96-2081 Filed 2-8-96; 8:45 am]
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