[Federal Register Volume 59, Number 130 (Friday, July 8, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-16612]
[[Page Unknown]]
[Federal Register: July 8, 1994]
_______________________________________________________________________
Part III
Department of Transportation
_______________________________________________________________________
Federal Aviation Administration
_______________________________________________________________________
14 CFR Part 23
Airworthiness Standards; Proposed Rule
=======================================================================
-----------------------------------------------------------------------
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 23
[Docket No. 27805; Notice No. 94-20]
RIN 2120-AE62
Airworthiness Standards; Airframe Proposals Based on European
Joint Aviation Requirements Proposals
AGENCY: Federal Aviation Administration, DOT.
ACTION: Notice of proposed rulemaking.
-----------------------------------------------------------------------
SUMMARY: This document proposes changes to the airframe airworthiness
standards for normal, utility, acrobatic, and commuter category
airplanes. These proposals arise from the joint effort of the Federal
Aviation Administration (FAA) and the European Joint Aviation
Authorities (JAA) to harmonize the Federal Aviation Regulations (FAR)
and the Joint Aviation Requirements (JAR) for airplanes that will be
certified in these categories. The proposed changes would provide
nearly uniform airframe airworthiness standards for airplanes
certificated in the United States under 14 CFR part 23 (part 23) and in
the JAA countries under Joint Aviation Requirements 23 (JAR 23)
simplifying airworthiness approvals for import and export purposes.
DATES: Comments must be submitted on or before November 7, 1994.
ADDRESSES: Comments on this document should be mailed in triplicate to:
Federal Aviation Administration, Office of the Chief Counsel,
Attention: Rules Docket (AGC-200), Docket No. 27805, 800 Independence
Avenue SW., Washington, DC 20591. Comments delivered must be marked
Docket No. 27805. Comments may be inspected in Room 915G weekdays
between 8:30 a.m. and 5 p.m., except on Federal holidays.
In addition, the FAA is maintaining an information docket of
comments in the Office of the Assistant Chief Counsel, ACE-7, Federal
Aviation Administration, Central Region, 601 East 12th Street, Kansas
City, Missouri 64106. Comments in the duplicate information docket may
be inspected in the Office of the Assistant Chief Counsel weekdays,
except Federal holidays, between the hours of 7:30 a.m. and 4 p.m.
FOR FURTHER INFORMATION CONTACT:
Kenneth W. Payauys, ACE-112, Small Airplane Directorate, Aircraft
Certification Service, Federal Aviation Administration, 601 East 12th
Street, Kansas City, Missouri 64106; telephone (816) 426-5688.
SUPPLEMENTARY INFORMATION:
Comments Invited
Interested persons are invited to participate in the making of the
proposed rule by submitting such written data, views, or arguments as
they may desire. Comments relating to the environmental, energy, or
economic impact that might result from adopting the proposals in this
notice are also invited. Substantive comments should be accompanied by
cost estimates. Comments should identify the regulatory docket or
notice number and should be submitted in triplicate to the Rules Docket
address specified above. All comments received on or before the
specified closing date for comments will be considered by the
Administrator before taking action on this proposed rulemaking. The
proposals contained in this notice may be changed in light of comments
received. All comments received will be available, both before and
after the closing date for comments, in the Rules Docket for
examination by interested persons. A report summarizing each FAA-public
contact concerned with the substance of this proposal will be filed in
the docket. Commenters wishing the FAA to acknowledge receipt of their
comments submitted in response to this notice must include a
preaddressed, stamped postcard on which the following statement is
made: ``Comments to Docket No. 27805.'' The postcard will be date
stamped and returned to the commenter.
Availability of NPRM
Any person may obtain a copy of this Notice of Proposed Rulemaking
(NPRM) by submitting a request to the Federal Aviation Administration,
Office of Public Affairs, Attention: Public Inquiry Center, APA-200,
800 Independence Avenue SW., Washington, DC 20591, or by calling (202)
267-3484. Communications must identify the notice number of this NPRM.
Persons interested in being placed on the mailing list for future
NPRM's should request, from the above office, a copy of Advisory
Circular No. 11-2A, Notice of Proposed Rulemaking Distribution System,
which describes the application procedure.
Background
At the June 1990 meeting of the JAA Council (consisting of JAA
members from European countries) and the FAA, the FAA Administrator
committed the FAA to support the harmonization of the FAR with the JAR
being developed for use by the European authorities who are members of
the JAA. In response to this commitment, the FAA Small Airplane
Directorate established an FAA Harmonization Task Force to work with
the JAR 23 Study Group to harmonize part 23 and the proposed JAR 23.
The General Aviation Manufacturers Association (GAMA) also established
a JAR 23/part 23 Committee to provide technical assistance in this
effort.
Following a review of the first draft of proposed JAR 23, members
of the FAA Harmonization Task Force and the GAMA Committee met in
Brussels, Belgium for the October 1990 meeting of the JAR 23 Study
Group. Representatives from the Association Europeenne des
Constructeures de Material Aerospatial (AECMA), an organization of
European airframe manufacturers, also attended. The main agenda item
for this meeting was the establishment of procedures to accomplish
harmonization of the airworthiness standards for normal, utility, and
acrobatic category airplanes. The JAA had decided that its initial
rulemaking effort should be limited to these three categories and that
commuter category airworthiness standards should be addressed
separately.
After that meeting, technical representatives from each of the four
organizations (GAMA, AECMA, FAA and JAA) met to resolve differences
between the proposed JAR and part 23. This portion of the harmonization
effort involved a number of separate meetings of specialists in the
flight, airframe, powerplant, and systems disciplines. These meetings
showed that harmonization would require revisions to both part 23 and
the proposed JAR 23.
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. The JAA and
the FAA held specialist and study group meetings to discuss these
recommendations, which resulted in proposals to revise portions of the
part 23 commuter category airworthiness standards.
Unlike the European rules, where commuter category airworthiness
standards are separate, for U.S. rulemaking it is advantageous to adopt
normal, utility, acrobatic, and commuter category airworthiness
standards simultaneously, since commuter category airworthiness
standards are already contained in part 23. Accordingly, this NPRM
proposes to revise the airframe airworthiness standards for all part 23
airplanes.
During the part 23 harmonization effort, the FAA established an
Aviation Rulemaking Advisory Committee (ARAC) (56 FR 2190, January 22,
1991), which held its first meeting on May 23, 1991. The ARAC on
General Aviation and Business Airplane (GABA) Issues was established at
that meeting to provide advice and recommendations to the Director,
Aircraft Certification Service, FAA, regarding the airworthiness
standards in part 23 as well as related provisions of parts 91 and 135
of the regulations.
The FAA announced, on June 2-5, 1992, at the JAA/FAA Harmonization
Conference in Toronto, Ontario, Canada, that it would consolidate
within the ARAC structure an ongoing objective to ``harmonize'' the JAR
and the FAR. Coinciding with that announcement, the FAA assigned the
ARAC on GABA Issues those rulemaking projects related to JAR/part 23
harmonization that were in final coordination between the JAA and the
FAA. The harmonization process included the intention to present the
results of JAA/FAA coordination to the public as NPRM's. Subsequently,
the ARAC on GABA Issues established an ARAC-JAR 23 Study Group.
The JAR 23 Study Group made recommendations to the ARAC on GABA
Issues concerning the FAA disposition of the rulemaking issues
coordinated between the JAA and the FAA. The draft NPRM's previously
prepared by the FAA harmonization team were made available to the
harmonization working group to assist them in their effort.
A notice of the formation of the JAR/FAR 23 Harmonization Working
Group was published on November 30, 1992 (57 FR 56626). The group held
its first meeting on February 2, 1993. These efforts resulted in the
proposals for airframe airworthiness standards contained in this
notice. The ARAC on GABA Issues agreed with these proposals.
The FAA received unsolicited comments from the JAA dated January
20, 1994, concerning issues that were left unresolved with the JAR 23
Study Group. The JAR/FAR 23 Harmonization Working Group did not address
some of the unresolved issues because the JAA had not yet reached
positions on those issues. Unresolved issues will be dealt with at
future FAR/JAR Harmonization meetings. With respect to other issues
unresolved by the JAR 23 Study Group, the JAR/FAR 23 Harmonization
Working Group recommendations did not reflect harmonization, but
reflected the technical discussion of the merits of each issue that had
been thoroughly debated at the JAR/FAR Harmonization meetings. (The
Working Group Chairperson had been present at the Harmonization
meetings.) The JAA comments have been placed in the docket for this
proposal, and will be considered along with those received during the
comment period.
Following completion of these harmonization efforts, the FAA
determined that the proposed revisions to part 23 were too numerous for
a single NPRM. The FAA decided to simplify the issues by issuing four
NPRM's. These NPRM's address the airworthiness standards in the
specific areas of systems and equipment, powerplant, flight, and
airframe. These NPRM's propose changes in all seven subparts of part
23. Since there is some overlap, interested persons are advised to
review all four NPRMs to identify all proposed changes to a particular
section.
Discussion of Proposals
Section 23.301 Loads
This proposal would amend Sec. 23.301(d) by limiting the
applicability of Appendix A to ``single-engine, excluding turbines''
airplanes rather than the current single-engine limitation. The JAA
proposed ``single reciprocating engine'' instead of ``single-engine,''
which appears in the current regulations. The FAA proposes ``single-
engine, excluding turbines'' for the reasons explained in the preamble
to Appendix A. The effect 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 may continue to be FAA certificated by
substantiation to part 23, Subpart C, requirements plus any special
conditions as prescribed under Sec. 21.16. The proposed changes to this
section clarify that Appendix A applies only to single-engine
airplanes, except turbines.
In Sec. 23.301(d), the phrase ``For conventional, single-engine
airplanes of 6,000 pounds or less'' would be replaced by the phrase
``For airplane configurations described in Appendix A23.1.''
Section 23.335 Design Airspeeds
Portions of Sec. 23.335 would be revised for clarification and
harmonization with JAR 23. Paragraph (a)(1) would be revised by adding
a definition for W/S as ``wing loading at the design maximum takeoff
weight.'' Paragraph (a)(1)(i) and (ii) would be revised 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).''
Section 23.335(b)(4) would be revised 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 is 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, would be corrected to VS1 ng.
Section 23.337 Limit Maneuvering Load Factors
Section 23.337(a)(1) would be revised 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.
Section 23.341 Gust Load Factors
Section 23.341 would be reorganized to provide a new paragraph (a)
that clarifies that each airplane must be designed to withstand loads
on each lifting surface that result from gusts specified in
Sec. 23.333(c). Existing paragraphs (a) and (b) would be redesignated
as (b) and (c), respectively. The text of the proposed paragraph (b)
would be revised to eliminate 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). The
reference to paragraph (b) in redesignated Sec. 23.341(b) is changed to
paragraph (c) to conform. The text for the redesignated paragraph (c)
would be revised to delete the phrase ``for conventional
configurations'' because it is no longer accurate, and to revise the
definition for wing loading (W/S). These changes are being proposed at
the request of the JAA to harmonize with JAR 23.
Section 23.343 Design Fuel Loads
Proposed new Sec. 23.343 would harmonize with the corresponding JAR
except for paragraph (c). This proposed requirement, which is a
modified version of Sec. 25.343 that covers transport category, would
apply to all part 23 airplane categories, except one paragraph that
would be limited to commuter category airplanes.
Airplanes already exist with ``maximum zero fuel'' weight limits
that apply to zero fuel in the airplane (wing, fuselage, and so forth),
rather than in the wing only. Therefore, ``maximum wing zero fuel''
weight was suggested for use when it is appropriate for the type of
fuel system in the design.
The FAA agreed, in a JAA/FAA Harmonization Study Group Meeting in
Vienna, in July 1992, to propose the requirements in three paragraphs.
The JAA would only propose paragraphs (a) and (b) for JAR 23 because
they do not have a 45-minute fuel reserve operating rule. Also, the JAA
decided to put paragraph (c) into a Notice of Proposed Action (NPA) to
await the creation of the necessary operating rule. In February 1993,
the same group agreed to have paragraph (b) address ``maximum zero wing
fuel'' weight, instead of ``maximum zero fuel'' weight as mentioned
above. The group agreed not to refer to the Operating Limitation
Section of the Airplane Flight Manual (AFM) required by proposed
Sec. 23.1583(c)(6) (as presented in the Flight Harmonization NPRM)
since that section already contains a reference to Sec. 23.343.
Section 23.345 High Lift Devices
Revised Sec. 23.345(a) would have minor, non-substantive,
clarifying changes. The term ``fully deflected'' would be changed to
``fully extended'' because it more accurately describes flap conditions
and positions. The phrase ``resulting in limit load factors'' would be
removed because the requirement already exists in Sec. 23.301(a).
Current paragraph (d) would be redesignated as paragraph (c) without
change.
Current paragraph (c) would be redesignated as paragraph (d) and
revised by including the requirements of Sec. 23.457. Paragraph (e)
would be deleted since it merely references the requirements of
Sec. 23.457, which have been moved to Sec. 23.345(d). This arrangement
places all ``flap'' requirements in one location, and would harmonize
the requirements with JAR 23.
Section 23.347 Unsymmetrical Flight Conditions
The proposed revision to Sec. 23.347 would redesignate the existing
text as paragraph (a) and add a new paragraph (b) that includes
requirements for a flick maneuver (snap roll), if requested for
aerobatic category airplanes. This change is being made to harmonize
with the JAR.
Section 23.349 Rolling Conditions
Section 23.349(a)(2) would be revised to simplify the unsymmetric
semispan load assumption to 100 percent and 75 percent for all design
weights up through 19,000 pounds. 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 agrees that 75 percent is an appropriate assumption
for all part 23 airplanes.
Section 23.369 Special Conditions for Rear Lift Truss
This proposal would amend Sec. 23.369 by amending the equation and
by adding a definition for wing loading (W/S) for clarification and to
harmonize with JAR 23.
Section 23.371 Gyroscopic and Aerodynamic Loads
Section 23.371(a) would be revised and reorganized by designating
the existing text as paragraph (a) and adding new paragraphs (b) and
(c).
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.'' These changes would clarify that these requirements apply
to all part 23 airplanes.
Proposed new paragraph (b) would clarify and distinguish the
requirements for airplanes approved for acrobatic maneuvers. These
clarifications are needed to harmonize with the JAR.
Proposed new paragraph (c) would 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). This clarification is
necessary to harmonize with the JAR.
Section 23.391 Control Surface Loads
This proposal would revise Sec. 23.391 by deleting paragraph (b)
and removing the designation for paragraph (a). Current paragraph (b)
is a reference to alternative values of control loading in Appendix B.
Appendix B was previously removed by Amendment No. 23-42 (56 FR 344,
January 3, 1991).
Section 23.393 Loads Parallel to Hinge Line
Proposed new Sec. 23.393, as suggested by the JAA, would contain a
modified version of the requirement of Sec. 23.657(c) concerning loads
parallel to the hinge line, which would be deleted from Sec. 23.657.
The requirement would specify minimum inertial load values, and be
included in new Sec. 23.393(b) to group the load factors in consecutive
sections.
Section 23.399 Dual Control System
Existing Sec. 23.399 does not address the forces exerted on a dual
control system when both pilots act together. The JAA has proposed
adding a new paragraph (b) to account for these pilot forces. The
material in present Sec. 23.399 would be reorganized as paragraph (a),
revised to clarify that it is the greater of the forces that apply, and
a new paragraph (b) would be added to include the JAA suggestion and
harmonize the rules.
Section 23.415 Ground Gust Conditions
This proposal would amend Sec. 23.415 by revising paragraph (a)(2)
to add a definition for wing loading (W/S) to harmonize with JAR 23. It
would also revise paragraph (c). Before paragraph (c) was added in
Amendment No. 23-45, the FAA agreed to a more comprehensive version of
the tie-down criteria that was suggested by the JAA. This amendment
would implement that agreement and harmonize the rules.
Section 23.441 Maneuvering Loads
The JAA suggested that Sec. 23.441(b) be revised to include a new
design requirement for the vertical tail of a commuter category
airplane. The JAA determined that the vertical tail structure must be
shown to be adequate for the loads imposed when the airplane is yawed
by rudder deflection to the maximum attainable angle and is suddenly
allowed to return by neutralizing the rudder. The maximum yaw condition
is governed by any of several constraining conditions; for example,
control surface stops, maximum available booster effort, or the various
maximum pilot rudder forces that may be imposed. The JAA stressed that
the design yaw excursions need to be examined throughout the full range
of speeds of the flight envelope. The FAA agrees. Although this is a
significant departure from the structural design philosophy depicted in
part 23 (full use of all controls at maneuvering speed) the addition of
a similar requirement to part 25 has served to reduce the static
overload failures in part 25 airplanes. It is expected that the
addition of the proposed requirement to Sec. 23.441(b) would reduce
this type failure in commuter category airplanes.
In addition, the permissible overswing angle that may be assumed
under Sec. 23.441(a)(2) would be changed from 1.3 to 1.5 times the
static sideslip angle of paragraph (a)(3). The JAA suggested that the
1.5 figure more closely represents reality. The FAA agrees and the rule
is changed to harmonize with the JAR. Finally, for clarification, the
word ``resulting'' is changed to ``overswing'' in the first sentence of
paragraph (a)(2).
Section 23.443 Gust Loads
Section 23.443(c) would be revised by changing the format of the
formula, revising the definition of weight, ``W,'' and correcting the
subscripts of the distance to the lift center, ``1vt.'' The
current definition reads ``W = airplane weight (lbs.).'' The proposed
definition reads ``W = the applicable weight of the airplane in the
particular load case (lbs.).'' The proposed changes are for clarity and
harmonization with JAR 23.
Section 23.455 Ailerons
The heading the precedes Sec. 23.455 would be amended by deleting
the term ``Wing Flaps'' so that the heading reads ``AILERONS AND
SPECIAL DEVICES.'' This change reflects the proposed deletion of the
wing flap requirements from Sec. 23.457 and their placement in
Sec. 23.345.
Section 23.457 Wing Flaps
The FAA proposes to delete this section. As discussed under
Sec. 23.345, above, the wing flap requirements have been revised and
consolidated in proposed Sec. 23.345 to group these requirements
together.
Section 23.473 Ground Load Conditions and Assumptions
The reference in Sec. 23.473(c)(1) would be revised. In amendment
No. 23-42 (January 3, 1991, 56 FR 344), Sec. 23.473(c)(1) incorrectly
continued to reference ``Sec. 23.67(a) or (b)(1).'' The reference in
Sec. 23.473(c)(1) should have been changed to ``Sec. 23.67(b)(1).''
The FAA also intends that turbine powered airplanes be included in
Sec. 23.473(c)(1) because these airplanes are required to be ``climb
positive'' with one engine inoperative. Therefore, Sec. 23.473(c)(1)
must also reference ``Sec. 23.67(c).''
Originally, the FAA intended to harmonize Sec. 23.473(c)(1) by
citing only Sec. 23.67. However, after considering the two issues noted
above, the FAA has determined that the intent described is lost unless
Sec. 23.473(c)(1) specifically includes ``Sec. 23.67(b)(1) or (c).''
Paragraph (f), which addresses energy absorption tests, would be
revised to parallel the language of JAR 23.473(f) with no substantive
change from current paragraph (f).
Section 23.497 Supplementary Conditions for Tail Wheels
Proposed new Sec. 23.497(c) would establish design standards for
the aft-mounted propellers of Sec. 23.925(b). The FAA has determined
that certain portions of the design standards for aft-mounted
propellers more properly belong in subpart C on structure. The
remainder of the standards would remain in subpart E.
Section 23.499 Supplementary Conditions for Nose Wheels
Proposed new Secs. 23.499 (d) and (e) would 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. Initial
versions of these two paragraphs were introduced at the Second
Structures Specialist Meeting, revised, and ratified by the JAR 23
Study Group in April 1991. The new paragraphs codify current
certification practice and distinguish the two types of control systems
to harmonize with JAR 23.
Section 23.521 Water Load Conditions
This proposal would amend Sec. 23.521 by deleting paragraph (c),
which was added by Amendment No. 23-45. The JAA pointed out that
paragraph (c) contains requirements already covered in paragraph (a).
The FAA agrees, and proposes to delete paragraph (c).
Section 23.561 General
This proposal would amend Secs. 23.561 (b), (d), and (e) by
revising the existing requirements to harmonize with JAR 23. Revised
paragraph (b), concerning occupant protection, proposes language
similar to part 25/JAR 25. Paragraph (d), concerning turnovers, would
be revised to simplify and clarify the requirements without making
substantive changes. Proposed new paragraph (e), concerning supporting
structure, would be revised to add references to Sec. 23.561(b)(3) and
Sec. 23.787(c) to ensure that items of mass are retained to higher
accelerations than the occupant for occupant protection.
Section 23.571 Metallic Pressurized Cabin Structures
Section 23.571 would be revised by changing the heading from
``Pressurized cabin'' to ``Metallic pressurized cabin structure''
because nonmetallic structure is addressed in Sec. 23.573(a). The
introductory text would be revised to limit the applicability to
normal, utility, and acrobatic category only because commuter category
airplanes are addressed separately. Paragraph (a) would be revised to
require the fatigue strength investigation to show that the structure
can withstand repeated loads of variable magnitude expected in service.
Currently, fatigue strength may be shown by tests or analysis or both.
Under the proposed revision, structural strength must be shown by tests
or by analysis supported by test evidence.
Section 23.572 Metallic Wing, Empennage, and Associated Structures
This proposal would revise the heading to add the word ``metallic''
and revise Sec. 23.572(a) to limit the applicability to normal,
utility, and acrobatic category airplanes and to make minor editorial
changes. Paragraph (a)(1) is revised to harmonize with JAR 23 by
requiring tests or analysis supported by test evidence, as discussed
under Sec. 23.571 of this preamble.
Section 23.573 Damage Tolerance and Fatigue Evaluation of Structure
This proposal would amend Sec. 23.573(a)(5) to clarify the
regulation because, as written, it could be easily misread. The
rewritten requirement uses the word ``any'' rather than ``each'' to
indicate that another limiting factor exists. It also changes the order
of the clauses to prevent the regulation from addressing ``failure of
the limit load capacity.'' The rewritten text makes it clear that
``Each bonded joint is required to be substantiated by tests'' is not
the desired result.
The FAA is not proposing a revision to paragraph (b) even though it
is not identical in format to JAR 23.573(b). While current FAR
Sec. 23.573(b) of title 14 contains two subparagraphs and JAR 23.573(b)
(JAR 23-Post Consultation) contains six subparagraphs, the two are
technically identical.
This proposal would delete Sec. 23.573(c). Inspections and other
procedures would be moved to Sec. 23.575 and be made applicable to four
sections pertaining to fatigue evaluation, namely, Secs. 23.571,
23.572, 23.573 and 23.574.
Technically, these actions harmonize with the efforts taken by the
JAA in similar paragraphs of JAR 23. JAR 23 contains identical
inspection requirements in JAR 23.571(b), JAR 23.572(c) and JAR
23.573(c). The FAA format is different from the JAR 23 presentation.
JAR 23 uses three paragraphs; proposed Sec. 23.575 uses one section to
accomplish the identical end result.
Section 23.574 Metallic Damage Tolerance and Fatigue Evaluation of
Commuter Category Airplanes
This proposal would add a new Sec. 23.574 that would delineate the
damage tolerance and fatigue evaluation requirement for commuter
category airplanes. The United Kingdom Civil Aviation Authority
proposed to revise JAR 23.571 and 23.572 to require commuter category
airplanes to meet the fail-safe provisions of those sections, and,
thus, remove the safe-life provisions. The FAA representative agree
with the intent of the proposal but could not agree with any specific
recommendation because the FAA was in the process of determining
requirements for commuter category airplanes in the aging aircraft
program. The majority of the subgroup decided they would not recommend
the United Kingdom Civil Aviation Authority proposal.
In the evaluation of aging aircraft, the FAA determined that new
commuter category airplanes must meet damage tolerance requirements.
The FAA then evaluated the damage tolerance procedures added by
Amendment No. 23-44, and the FAA is now proposing to add new
Sec. 23.574 that would require commuter category airplanes to comply
with the damage tolerance and fatigue evaluation of Sec. 23.573.
Accordingly, as discussed previously, Secs. 23.571 and 23.572 would be
revised to clarify that these sections would 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.
JAR 23 Structures Specialists and the JAR 23 Study Group agree with
these requirements and consider the impact upon the JAR 23 effort; they
decided to place JAR 23.574 on the NPA list. By these actions, the JAA
and the FAA will propose the same damage tolerance provisions for newly
certificated commuter category airplanes.
Section 23.575 Inspections and Other Procedures
This proposal would add a new Sec. 23.575 that would clarify that
airplane manufacturers are required to provide recommendations for
inspection frequencies, locations and methods when the design is
approved by the FAA. Whether these inspections and procedures are
required has been unclear for the past 20 years. This proposal
clarifies that. Both safe-life and damage-tolerant airplane designs
would be involved. Also, both composite and metallic airplanes would be
included.
Section 23.573(c) would be moved to Sec. 23.575 and revised. The
revision consists of naming those requirements that are included,
namely Secs. 23.571, 23.572, 23.573 and 23.574. These four sections
address pressurized cabin, wing, empennage (tail), and associated
structures for metallic airplanes. They also provide standards for
damage tolerance and fatigue evaluations of both composite and metallic
airplane structures. Proposed Sec. 23.575 would harmonize these rules
with JAR 23 technically, but a simple format.
Section 23.607 Fasteners
This proposal would amend Sec. 23.607 by changing the section
heading, by redesignating the existing requirement as paragraph (c),
and by adding new paragraphs (a) and (b) to require the following: if
the loss of a non-selflocking fastener would preclude continued safe
flight and landing, a locking device must be incorporated, and the
fastener must not be adversely affected by environmental conditions
such as temperature or vibration. These requirements would be added for
harmonization.
Section 23.611 Accessibility Provisions
Structural specialists from both the JAA and FAA agreed that
Sec. 23.611, Accessibility, is unclear in its intent and examples would
be an aid to understanding.
The proposed revision would clarify the requirement. In the
Instructions for Continued Airworthiness required under Sec. 23.1529,
recommended or required inspection items to which access must be
provided are identified. Following are examples of such items: (1)
Principle structural elements and control system components that
require inspection; (2) replaceable parts; and (3) parts that require
adjustment or lubrication. Section 23.611 requires that, for any part
requiring servicing, there must be a means of access incorporated into
the aircraft design to allow this servicing to be accomplished. Whether
the access provided is appropriate will depend on the nature of the
item, and the frequency and complexity of the required inspection or
maintenance actions.
Section 23.629 Flutter
Section 23.629 would be revised 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 JAA argues that unless
the rational analysis or simplified analysis is verified by some flight
flutter tests, the validity of such an analysis is unknown. The JAA
also points out that the extent of flight flutter testing depends upon
the analysis prepared and the experience with similar designs. The FAA
structures specialist agreed with these arguments and with harmonizing
this section, even though it would represent an increased requirement
for substantiation. These changes would be enacted by proposed
revisions to Sec. 23.629 (a), (b), and (c), noting that the
designations of paragraphs (b) and (c) would be switched. Paragraph
(d)(3)(i) would be revised 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.
Also, Amendment No. 23-45 added Sec. 23.629 (g) and (h), which
contain the phrase ``by analysis or test'' and is consistent with the
original part 23 requirement in Sec. 23.629(a); that is, the applicant
is able to choose the method of substantiation. JAR 23.629 (g) and (h)
propose that substantiation be done only ``by analysis.'' The JAA
argues that the analysis required by the rule must be based upon a
previously verified flutter analysis model. The JAA notes that this
requirement exists in Sec. 23.629(a), which generally states that full
scale flight flutter tests must be conducted when the adequacy of
flutter analysis and wind tunnel tests have not been established by
previous experience with airplanes having similar design features, and
when modifications to the type design have a significant effect upon
the critical flutter modes. The FAA proposes to harmonize with JAR 23
by amending Sec. 23.629 (g) and (h) to remove the ``or test'' phrase.
For an airplane that has undergone modification that could affect its
flutter characteristics, proposed paragraph (i) 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.
Section 23.657 Hinges
This proposal would amend Sec. 23.657 by deleting paragraph (c),
which covers loads parallel to the hinge line. As discussed above, this
requirement would be moved to keep the load factors in consecutive
regulatory sections.
Section 23.673 Primary Flight Controls
A proposed revision to Sec. 23.673 would delete the requirements
for two-control airplanes consistent with actions being taken in the
Flight Harmonization NPRM Secs. 23.177 and 23.201. The two-control
airplane regulations were introduced in 1945 but no two-control
airplanes have been certificated for several decades and no need is
foreseen for these regulations. If an applicant proposes a two-control
airplane, the FAA would issue special conditions. Accordingly,
Sec. 23.673(b) and the paragraph (a) indicator, since it is no longer
needed, are deleted.
Additional harmonization with JAR 23 is accomplished by this
action.
Section 23.725 Limit Drop Tests
This proposal would amend Sec. 23.725 by adding brackets to clarify
the effective weight equation in paragraph (b).
Section 23.755 Hulls
This proposal would amend Sec. 23.755 by deleting paragraph (b),
which provides that keels of hull seaplanes or amphibians of less than
1,500 pounds need not be compartmented and which is redundant with
paragraph (a). The proposal would also redesignate paragraph (c) as new
paragraph (b) and edit it for clarification.
Section 23.865 Fire Protection of Flight Controls, Engine Mounts, and
Other Flight Structures
This section on fireproof material and shielding would be revised
by changing the words ``engine compartment'' to ``designated fire
zones'' to be consistent with recent revisions to Secs. 23.1203 and
23.1181. The revision would include the phrase ``adjacent areas that
would be subjected to the effects of fire in the designated fire
zones.'' Adding this phrase clarifies FAA practice that areas in and
around a designated fire zone must also be protected, and harmonizes
the rule with JAR 23.
Section 23.925 Propeller Clearance
This proposal would 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 above. The inspection/
replacement criteria for tail wheel, bumper, and energy absorption
device would be deleted because the inspection/replacement is required
in Sec. 23.1529 and does not need to be repeated here.
Appendix A
Three areas of Appendix A would be revised: (1) A23.1 General; (2)
A23.11 Control surface loads, paragraph (c), Surface loading
conditions; and (3) Table 2--Average limit control surface loading. A
new figure would be added to Appendix A: Figure A7, Chordwise load
distribution for stabilizer and elevator, or fin and rudder. These
proposed revisions are based upon limitations in JAR 23, Appendix A.
They are needed to specify the configurations for which the wing and
tail surface loads, required in A23.7, are valid.
The title of Appendix A is revised by removing the words ``for
conventional, single-engine airplanes of 6,000 pounds or less maximum
weight,'' because the weight limitation is unnecessary in the title and
appears in paragraph A23.1(a).
In A23.1, existing paragraph (a) would be revised extensively, and
existing paragraph (b) would be deleted and replaced by new paragraph
(b). The word ``conventional'' would be removed and replaced by ten
subparagraphs that more accurately describe what is meant by that term.
The term ``single engine'' is changed to ``single engine, excluding
turbines'' to clarify the applicability of the Appendix. This change
would permit the use of a rotary engine. Note that this was
accomplished in JAR-VLA and AC 23-11 by using the term ``single engine
(spark- or compression-ignition).'' The format differs from that
originally proposed and agreed to by JAA/FAA structures specialists.
However, the technical content remains the same. The JAA believes that
these criteria represent those envisioned when Appendix A was first
introduced.
Clarifying changes would be made to A23.11, paragraph (c)(1). Then,
six paragraphs and a diagram, with defined terms, would be added to
specify and clarify the conditions that apply. Paragraph (d) would be
revised to correct a section reference.
The Chordwise Distribution for the Horizontal Tail I portion of
Table 2 would be deleted and replaced by the reference ``See Figure
A7'' so that a more appropriate design load may be applied. The
Vertical Tail II portion of Table 2 would be corrected by removing the
(a) and (b) references, and duplicate statements, so that ``Right and
Left,'' ``Figure A5 Curve (1),'' and ``Same as above'' remain in the
columns.
A new Figure A7 would be added to define both the chordwise load
distribution and its corresponding parameters.
Regulatory Evaluation Summary
Preliminary Regulatory Evaluation, Initial Regulatory Flexibility
Determination, and Trade Impact Assessment
Proposed changes to Federal regulations must undergo several
economic analyses. First, Executive Order 12866 directs that each
Federal Agency shall propose or adopt a regulation only upon a reasoned
determination that the benefits of the intended regulation justify its
costs. Second, the Regulatory Flexibility Act of 1980 requires agencies
to analyze the economic effects of regulatory changes on small
entities. Third, the Office of Management and Budget directs agencies
to assess the effects of regulatory changes on international trade. In
conducting these analyses, the FAA has determined that this rule: (1)
would generate benefits that justify its costs and is not a
``significant regulatory action'' as defined in the Executive Order;
(2) is not significant as defined in DOT's Policies and Procedures; (3)
would not have a significant impact on a substantial number of small
entities; and (4) would not constitute a barrier to international
trade. These analyses, available in the docket, are summarized below.
Regulatory Evaluation Summary
Of the part 23 sections that would be amended or added, the FAA has
identified only 6 that would result in additional compliance costs,
totalling between $12,000 and $20,000 per certification. When amortized
over a production run, these costs would have a negligible impact on
the cost per airplane. The FAA solicits comments concerning the
incremental certification/development costs attributable to the
proposed rule.
The primary benefit of the proposed rule would be the cost
efficiencies of harmonization with the JAR for those manufacturers who
choose to market airplanes in JAA countries as well as to manufacturers
in JAA countries who choose to market airplanes in the United States.
Other benefits of the proposed rule would 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 proposed rule would 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 proposed amendments would not have a significant economic
impact on a substantial number of small entities.
International Trade Impact Assessment
The proposed rule would not constitute a barrier to international
trade, including the export of American goods and services to foreign
countries and the import of foreign goods and services into the United
States. Instead, the proposed airframe certification procedures would
be harmonized with those of the JAA and would lessen restraints on
trade.
Federalism Implications
The regulations proposed 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,
according to Executive Order 12612, it is determined that this proposal
would not have sufficient federalism implications to warrant the
preparation of a Federalism Assessment.
Conclusion
The FAA proposes to revise the airframe airworthiness standards for
normal, utility, acrobatic, and commuter category airplanes to
harmonize them with the standards that were published for the same
category airplanes by the Joint Airworthiness Authorities in Europe. If
adopted, the proposed revisions would 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 a different country.
For the reasons discussed in the preamble, and based on the
findings in the Regulatory Evaluation, the FAA has determined that this
proposed regulation is not significant under Executive Order 12866. In
addition, the FAA certifies that this proposal, if adopted, would not
have a significant economic impact on a substantial number of small
entities under the criteria of the Regulatory Flexibility Act. This
proposal is not considered significant under DOT Regulatory Policies
and Procedures (44 FR 11034, February 26, 1979). An initial regulatory
evaluation of the proposal 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 Proposed Amendment
In consideration of the foregoing, the Federal Aviation
Administration proposes to amend part 23 of the Federal Aviation
Regulations (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. app. 1344, 1354(a), 1355, 1421, 1423, 1425,
1428, 1429, 1430; 49 U.S.C. 106(g).
2. Section 23.301 is amended by revising paragraph (d) 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,
section A23.1, 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 paragraphs (a)(1)
introductory text, (a)(1)(i), and (a)(1)(ii); by removing the period
and adding ``; and either'' 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 is amended by revising paragraph (a)(1) to read
as follows:
Sec. 23.337 Limit maneuvering load factors.
(a) * * *
TP08JY94.004
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:
TP08JY94.005
* * * * *
W/S=Wing loading (p.s.f.) due to 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
1.8VSF, 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.
However, 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 on the other side.
* * * * *
10. Section 23.369(a) is revised to read as follows:
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 acrobatic maneuvers, each engine
mount and its supporting structures must be designed to withstand the
combined maximum yaw velocity, pitch velocity, and corresponding load
factors expected during such maneuvers.
(c) For commuter category airplanes, the gust conditions specified
in Sec. 23.341 must be added to the conditions required by paragraph
(a) of this section.
Sec. 23.391 [Amended]
12. Section 23.391 is amended by removing paragraph (b) and
removing the designation ``(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
TP08JY94.010
BILLING CODE 4910-13-C
(2) The rudder must be suddenly displaced from the maximum
deflection to the neutral position.
* * * * *
17. Section 23.443 is amended by revising paragraph (c) 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:
TP08JY94.006
where--
Lvt=Vertical surface loads (lbs.);
TP08JY94.007
TP08JY94.008
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 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 paragraph (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 mechanical
connection to the rudder pedals, the steering torque must be designed
to withstand 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 the introductory text of
paragraph (b); by revising paragraphs (d)(1)(i) through (d)(1)(iv); by
removing paragraph (d)(1)(v); 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 and by
revising paragraphs (a) introductory text and (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 in its place
``Sec. 23.571(a)(3)''; 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) * * *
(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 non-self-locking bolt, screw, nut, pin, or other fastener
must, if its loss would preclude continued safe flight and landing,
incorporate a locking device.
(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 paragraph (b) as paragraph (c)
and revising it; by redesignating existing paragraph (c) as paragraph
(b) and revising its introductory text; 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) * * *
TP08JY94.014
* * * * *
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 designed 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 title, section A23.1,
paragraphs A23.11 (c)(1) and (d), and Table 2; and by adding Figure A7
to the end of the Appendix read as follows:
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 turbines;
(2) A main wing located closer to the airplane's center of
gravity than the aft, fuselage-mounted, empennage;
(3) A main wing that contains a quarter-chord sweep angle of not
more that 15 degrees fore and 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 planform area not greater than 10 percent of
the wing planform area; and
(10) Symmetrical airfoils must be used in both the horizontal
and vertical tail designs.
(b) This 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 planforms (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 balanced surfaces.
(ii) The load on the stabilizer and elevator, and the load on
fin and rudder, must be distributed chordwise as shown in Figure A7
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:
TP08JY94.009
BILLING CODE 4910-13-M
TP08JY94.011
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.
* * * * *
BILLING CODE 4910-13-M
TP08JY94.012
TP08JY94.013
BILLING CODE 4910-13-C
Issued in Washington, DC, on July 5, 1994.
Thomas E. McSweeny,
Director, Aircraft Certification Service.
[FR Doc. 94-16612 Filed 7-7-94; 8:45 am]
BILLING CODE 4910-13-M