[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]


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Part III





Department of Transportation





_______________________________________________________________________



Federal Aviation Administration



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14 CFR Part 23



Airworthiness Standards; Proposed Rule
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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.

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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