Aging Aircraft Program: Widespread Fatigue Damage, 19928-19951 [06-3621]

Agencies

• Federal Aviation Administration
• DEPARTMENT OF TRANSPORTATION

[Federal Register Volume 71, Number 74 (Tuesday, April 18, 2006)]
[Proposed Rules]
[Pages 19928-19951]
From the Federal Register Online via the Government Printing Office [www.gpo.gov]
[FR Doc No: 06-3621]



[[Page 19927]]

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Part II





Department of Transportation





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Federal Aviation Administration



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14 CFR Parts 25, 121, and 129



Aging Aircraft Program: Widespread Fatigue Damage; Proposed Rule

Federal Register / Vol. 71, No. 74 / Tuesday, April 18, 2006 / 
Proposed Rules

[[Page 19928]]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Parts 25, 121, and 129

[Docket No. FAA-2006-24281; Notice No. 06-04]
RIN 2120-AIO5


Aging Aircraft Program: Widespread Fatigue Damage

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking.

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SUMMARY: This action is intended to prevent widespread fatigue damage 
by proposing to require that design approval holders establish 
operational limits on transport category airplanes. Design approval 
holders would also be required to determine if maintenance actions are 
needed to prevent widespread fatigue damage before an airplane reaches 
its operational limit. Operators of any affected airplane would be 
required to incorporate the operational limit and any necessary service 
information into their maintenance programs. Operation of an affected 
airplane beyond the operational limit would be prohibited, unless an 
operator has incorporated an extended operational limit and any 
necessary service information into its maintenance program.

DATES: Send your comments on or before July 17, 2006.

ADDRESSES: You may send comments [identified by Docket Number FAA-2006-
24281] using any of the following methods:
     DOT Docket Web site: Go to https://dms.dot.gov and follow 
the instructions for sending your comments electronically.
     Government-wide rulemaking Web site: Go to https://
www.regulations.gov and follow the instructions for sending your 
comments electronically.
     Mail: Docket Management Facility; U.S. Department of 
Transportation, 400 Seventh Street, SW., Nassif Building, Room PL-401, 
Washington, DC 20590-0001. Due to the suspension of paper mail delivery 
to DOT headquarters facilities, we encourage commenters to send their 
comments electronically.
     Fax: 1-202-493-2251.
     Hand Delivery: Room PL-401 on the plaza level of the 
Nassif Building, 400 Seventh Street, SW., Washington, DC, between 9 
a.m. and 5 p.m., Monday through Friday, except Federal holidays.
    For more information on the rulemaking process, see the 
SUPPLEMENTARY INFORMATION section of this document.
    Privacy: We will post all comments we receive, without change, to 
https://dms.dot.gov, including any personal information you provide. For 
more information, see the Privacy Act discussion in the SUPPLEMENTARY 
INFORMATION section of this document.
    Docket: To read background documents or comments received, go to 
https://dms.dot.gov at any time or to Room PL-401 on the plaza level of 
the Nassif Building, 400 Seventh Street, SW., Washington, DC, between 9 
a.m. and 5 p.m., Monday through Friday, except Federal holidays.

FOR FURTHER INFORMATION CONTACT: Walter Sippel, FAA, Transport Airplane 
Airframe/Cabin Safety Branch, ANM-115, Transport Airplane Directorate, 
Aircraft Certification Service, 1601 Lind Avenue, SW., Renton, WA 
98039-4056; telephone (425) 227-2774, fax (425) 227-1232.

SUPPLEMENTARY INFORMATION:

Comments Invited

    The FAA invites interested persons to participate in this 
rulemaking by submitting written comments, data, or views. We also 
invite comments relating to the economic, environmental, energy, or 
federalism impacts that might result from adopting the proposals in 
this document. The most helpful comments reference a specific portion 
of the proposal, explain the reason for any recommended change, and 
include supporting data. We ask that you send us two copies of written 
comments.
    We will file in the docket all comments we receive, as well as a 
report summarizing each substantive public contact with FAA personnel 
concerning this proposed rulemaking. The docket is available for public 
inspection before and after the comment closing date. If you wish to 
review the docket in person, go to the address in the ADDRESSES section 
of this preamble between 9 a.m. and 5 p.m., Monday through Friday, 
except Federal holidays. You may also review the docket using the 
Internet at the web address in the ADDRESSES section.
    Privacy Act: Using the search function of our docket Web site, 
anyone can find and read the comments received into any of our dockets, 
including the name of the individual sending the comment (or signing 
the comment on behalf of an association, business, labor union, etc.). 
You may review DOT's complete Privacy Act statement in the Federal 
Register published on April 11, 2000 (65 FR 19477-78) or you may visit 
https://dms.dot.gov.
    Before acting on this proposal, we will consider all comments we 
receive on or before the closing date for comments. We will consider 
comments filed late if it is possible to do so without incurring 
expense or delay. We may change this proposal in light of the comments 
we receive.
    If you want the FAA to acknowledge receipt of your comments on this 
proposal, include with your comments a preaddressed, stamped postcard 
on which the docket number appears. We will stamp the date on the 
postcard and mail it to you.

Availability of Rulemaking Documents

    You can get an electronic copy using the Internet by:
    (1) Searching the Department of Transportation's electronic Docket 
Management System (DMS) Web page (https://dms.dot.gov/search).
    (2) Visiting the Office of Rulemaking's Web page at https://
www.faa.gov/avr/arm/nprm.cfm?nav=nprm; or
    (3) Accessing the Government Printing Office's Web page at https://
www.access.gpo.gov/su_docs/aces/aces140.html.
    You can also get a copy by sending a request to the Federal 
Aviation Administration, Office of Rulemaking, ARM-1, 800 Independence 
Avenue, SW., Washington, DC 20591, or by calling (202) 267-9680. Make 
sure to identify the docket number, notice number, or amendment number 
of this rulemaking.

I. Executive Summary

    The rule proposed today would establish operational limits for 
transport category airplanes to preclude widespread fatigue damage 
(WFD). It would also require actions to prevent WFD in repairs, 
alterations, and modifications \1\ to these airplanes. This proposal 
should preclude WFD from occurring in transport category airplanes by 
providing a more proactive management of WFD.
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    \1\ Throughout this proposal, reference is made to 
``alterations'' and ``modifications.'' We consider these terms to be 
synonymous. An ``alteration'' is a design change that is made to an 
airplane; however, various segments of industry have also defined 
these changes as ``modifications.'' Therefore, we use both terms in 
the proposed rule to be all inclusive of any design change and to 
avoid potential misinterpretation of the intent of these terms.
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    This proposal would require type certificate (TC) holders to 
establish an initial operational limit on certain airplanes. Operation 
of these airplanes beyond the initial operational limit would be 
prohibited, unless operators have incorporated an extended operational 
limit into their maintenance programs. Type certificate holders would 
be required to develop the initial

[[Page 19929]]

operational limits based on an evaluation of WFD susceptibility, both 
for existing airplanes and for proposed future certifications. For 
future type certification, all TC applicants for transport category 
airplanes would be affected. For existing type certificates, this 
proposal would affect only airplanes with maximum takeoff gross weights 
(MTGW) over 75,000 pounds, including airplanes that have had the MTGW 
increased to greater than 75,000 pounds. (These airplanes are referred 
to in this document as large transport category airplanes.) 
Supplemental type certificate (STC) holders for these airplanes would 
be required to evaluate their STCs for WFD and the ability of the 
airplane to remain free of WFD up to the initial operational limit 
established by the TC holder.
    Once the proposed initial operational limits are developed, then 
operational rules in parts 121 and 129 would require operators to 
incorporate initial operational limits into their maintenance programs. 
The proposed operational rules would prohibit operation beyond the 
limit established for an airplane. However, the proposed design 
approval holder and operational rules would provide means for any 
person to extend the initial operational limit and for operators to 
operate an airplane under the extended operational limit. If an 
extended operational limit is incorporated, the proposed operational 
rules would prohibit operation beyond the extended operational limit 
established for an airplane. In addition, the proposed operational 
rules would address repairs, alterations, and modifications to 
airplanes operating with an extended operational limit.
    The present value benefits of this proposal consist of $726 million 
of accident prevention benefits and $83 million of detection benefits 
for total benefits of $809 million. The detection benefits are the 
benefits resulting from averted accidents and a reduction in 
unscheduled maintenance and repairs. The present value cost of this 
proposal, estimated over 20 years, is $360 million. The FAA estimates 
that airplane manufacturers would incur approximately 10 percent of 
these costs, while the remaining 90 percent of these costs would be 
borne by operators.

II. Background

A. Widespread Fatigue Damage

    WFD is the simultaneous presence of cracks at multiple structural 
locations that are of sufficient size and density such that the 
structure will no longer meet the residual strength requirements of 
section 25.571(b). Fatigue damage is the gradual deterioration of a 
material subjected to repeated loads. Airplane structure experiences 
fatigue damage because it is subjected to repeated loads, such as the 
pressurization and depressurization of an airplane that occurs with 
each flight. The fatigue damage could result in cracks occurring in 
structure over time.
    The likelihood of WFD in airplane structure increases with use. WFD 
results from many cracks that are generally too small to be reliably 
detected using existing inspection methods. These cracks could grow 
together very rapidly, so that failure could occur before another 
inspection is performed to detect them. The simultaneous presence of 
fatigue cracks that may grow together, with or without other damage in 
the same structural element, such as a large skin panel, is known as 
multiple site damage. The simultaneous presence of fatigue cracks in 
similar adjacent structural elements, such as frames and stringers, is 
known as multiple element damage. Some structural elements can be 
susceptible to both types of damage, which potentially could occur at 
the same time. If undetected, either type of damage could lead to 
catastrophic failure due to reduction of the strength capability of the 
structure.
    The FAA, the European Joint Aviation Authorities, and 
representatives of the Airworthiness Assurance Working Group, working 
under the support of the Aviation Rulemaking Advisory Committee (ARAC), 
reviewed available service difficulty reports for the transport 
airplane fleet. They also evaluated the certification and design 
practices applied to these previously certificated airplanes, including 
fatigue test results. The review revealed that all airplanes in the 
fleet are susceptible to multiple site damage or multiple element 
damage. Table 1 identifies examples of structures susceptible to 
multiple site damage (MSD) and multiple element damage (MED).

   Table 1.--Examples of Structures Susceptible to Widespread Fatigue
                                 Damage
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                 Structure                         Susceptible to
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Longitudinal skin joints, frames and tear   MSD/MED
 straps.
Circumferential joints and stringers......  MSD/MED
Fuselage frames...........................  MED
Lap joints with milled, chem.-milled, or    MSD
 bonded radius.
Stringer-to-frame attachments.............  MED
Shear clip end fasteners on shear tied      MSD/MED
 fuselage.
Aft pressure dome outer ring and dome web   MSD/MED
 splices.
Skin splice at aft pressure bulkhead......  MSD
Abrupt changes in web or skin thickness     MSD/MED
 (pressurized or unpressurized structure).
Window surround structure.................  MSD/MED
Overwing fuselage attachments.............  MED
Latches and hinges of nonplug doors.......  MSD/MED
Skin at runout of large doubler (MSD),      MSD
 fuselage, wing, or empennage.
Rib to skin attachments...................  MSD/MED
Typical wing or empennage structure.......  MSD/MED
Wing and empennage chordwise splices......  MSD/MED
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B. History of WFD in Transport Category Airplanes

    In April 1988, an 18-foot section of the upper fuselage of an Aloha 
Airlines Boeing Model 737 airplane separated from the airplane en route 
from Hilo to Honolulu, Hawaii. The National Transportation Safety Board 
determined that, among other things, WFD was a contributing cause of 
this accident. Since then, WFD appears to have played a role in several 
safety incidents involving large transport airplanes, although there 
has not been a catastrophic accident directly attributable to WFD. In 
particular, the FAA has issued or is in the process of issuing 
Airworthiness Directives (ADs) addressing aft pressure bulkhead cracks, 
lap splice cracks, and frame cracks.

C. Industry Input/Aviation Rulemaking Advisory Committee

    The FAA has tasked the ARAC to address several issues related to 
widespread fatigue damage. In 2001, the ARAC recommended imposing a 
limit on the validity of maintenance programs, requiring an evaluation 
of repairs, alterations and modifications, and providing a means of 
extending the limit of validity of the maintenance program for large 
transport category airplanes. The ARAC also recommended that elements 
of the existing aging airplane program be included or referenced in the 
Airworthiness Limitations section (ALS) of the Instructions for 
Continued Airworthiness (ICA). In 2003, the ARAC recommended imposing a 
limit on the validity of maintenance programs for all

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newly certificated transport category airplanes.
    The ARAC recognized that structural fatigue characteristics of 
airplanes are only understood up to a point in time consistent with the 
analyses performed and the amount of testing accomplished. The 
maintenance program inspections related to structural fatigue are based 
on the results of these analyses and tests. Therefore, these 
inspections may need to be supplemented by further inspections, 
modifications, or replacements, if operation beyond a certain point is 
planned. The ARAC recommended that there should be a ``limit of 
validity of the maintenance program'' to limit the operation of an 
airplane. Once an airplane reached this limit, the operator should no 
longer operate the airplane, unless the operator has incorporated an 
extended limit of validity and any necessary service information into 
its maintenance program.

D. Current Regulations and Programs Related to WFD

1. Existing Design Criteria
    In the design process, a type certificate applicant generally 
establishes an expected economic life for the airplane, known as a 
design service goal. Applicants traditionally defined the design 
service goal early in the development of a new airplane, based on 
economic analyses, past service experience with prior models, and in 
some cases fatigue testing. Design approval holders have also performed 
additional fatigue tests, teardown inspections, and analyses to support 
changing design service goals to extended service goals. The 
regulations required applicants and design approval holders only to 
show that individual fatigue cracks would not lead to catastrophic 
structural failure. Since 1978, 14 CFR 25.571 has required applicants 
for new type certificates for transport category airplanes to establish 
inspections to detect fatigue cracks before they can grow to the point 
of catastrophic failure (43 FR 46242, October 5, 1978). These 
inspections are documented in the ALS.
    In 1998, the FAA amended the aircraft certification requirements 
for transport category airplanes (63 FR 15707, March 31, 1998). As part 
of the certification process, section 25.571 now requires full-scale 
fatigue test evidence to demonstrate that WFD will not occur before an 
airplane reaches its design service goal. Only a few airplane models 
are subject to this new requirement, because the applications for most 
type certificates predate 1998. Even with the requirement to perform 
full-scale fatigue testing, there is no requirement to limit the 
operation of an airplane once it reaches the design service goal.
2. Instructions for Continued Airworthiness
    As part of the current certification process, TC holders and STC 
holders who applied for a certificate after January 28, 1981 are 
required by Sec.  21.50 to make available at least one set of complete 
ICA to the owner of the airplane. The ICA must include inspection and 
replacement instructions for airplane structure. Also, any person who 
makes a design change to airplane structure must provide the airplane 
owner with a complete set of the ICA for that change.
    In developing the ICA, the applicant is required to include certain 
information, such as a description of the airplane and its systems, 
servicing information, and maintenance instructions (Sec.  25.1529). 
The applicant must include the frequency and extent of the structural 
inspections necessary to provide for the continued airworthiness of the 
airplane as well as an FAA-approved ALS listing all mandatory 
inspections, inspection intervals, replacement times, and related 
procedures. The FAA requires operators to comply with each ALS 
established under Sec.  25.1529 for newly certified airplanes or with 
operation specifications approved under part 121 or 135. Operators may 
also incorporate tasks--from a Maintenance Review Board document that 
has been approved by the FAA \2\--into their maintenance program.
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    \2\ The FAA establishes a Maintenance Review Board comprised of 
subject matter experts who oversee development of a maintenance 
program for a specific airplane. In conjunction with the work of the 
review board, an industry steering committee comprised of 
representatives from the applicant, operators, and the FAA, analyzes 
maintenance requirements for that specific airplane. The review 
board and the steering committee then produce a Maintenance Review 
Board document that contains, among other task, inspections of the 
airplane structure. These inspections, in conjunction with any 
airworthiness limitation items established under Sec.  25.271, 
address accidental damage environmental damage, and fatigue damage.
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3. Airworthiness Directives
    The FAA currently issues ADs when we find that an unsafe condition 
exists in a product and the condition is likely to exist or develop in 
other products of the same type design. Because WFD could lead to a 
catastrophic failure due to reduction of the strength capability of the 
structure, we would issue an AD to address a finding of WFD in a 
particular product. An AD typically addresses an unsafe condition by 
requiring inspection, modification, or replacement of certain 
structure, or a combination of these approaches. ADs are reactive and 
address only known instances of WFD. Additionally, ADs are directed 
towards a specific group of airplanes. Hence, WFD may go undetected in 
other airplanes with similar structures.
4. Aging Aircraft Program
    In October 1991, Congress enacted the Aging Aircraft Safety Act of 
1991 (49 U.S.C. 44717) to address aging aircraft concerns. In response 
to the Act, the FAA published an interim final rule that amended 
Sec. Sec.  121.368, 121.370a, 129.16, and 129.33 of the air carrier 
operating rules (67 FR 72726, December 6, 2002). Sections 121.368 and 
129.33 require mandatory records reviews and airplane inspections after 
the airplane has been in service 14 years. In addition, Sec. Sec.  
121.370a and 129.16 require damage-tolerance-based inspections and 
procedures on airplanes operated under 14 CFR parts 121 and 129, 
respectively.
    In response to the Aloha Airlines accident, the FAA formed the 
Airworthiness Assurance Task Force to investigate and propose solutions 
to the problems evidenced as a result of the accident. The task force 
was comprised of operators, manufacturers, and regulatory authorities. 
The task force recommended establishment of an Aging Airplane Program. 
Under the Aging Airplane Program, the FAA has mandated the following 
four separate programs:
     Supplemental Structural Inspection Programs for certain 
large transport category airplanes;
     Corrosion Prevention and Control Programs for certain 
large transport category airplanes;
     Repair Assessment Program to ensure existing and future 
repairs to the fuselage pressure boundary are assessed for damage 
tolerance.
     Mandatory Modification Program, based on the premise that 
to ensure the structural integrity of older airplanes there should be 
less reliance on repetitive inspections. (The determination of whether 
a modification is required is based on meeting certain criteria.)
    These four programs or their equivalent make up the current 
structural maintenance program that operators incorporate into their 
maintenance or inspection programs to address aging structures. 
However, none of the programs address widespread fatigue damage.

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5. Advisory Circulars
    We have considered issuing Advisory Circulars (ACs) to give 
guidance on the changes needed to prevent WFD. Advisory Circulars, 
however, depend on voluntary compliance and are not enforceable. 
Therefore, use of ACs alone would ensure neither consistent results nor 
achievement of the WFD safety objectives for the current and future 
fleet.\3\
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    \3\ Voluntary safety assessments, such as those relating to the 
thrust reverser and cargo door reviews, have been difficult to 
complete in a timely manner because they lacked enforceability.
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E. Summary of the Proposal

    Long-term reliance on existing requirements, even those that 
incorporate the latest mandatory changes introduced to combat 
structural degradation due to WFD, creates a risk of structural failure 
and related accidents because the requirements are inadequate to 
preclude WFD.
    To address WFD, we need a proactive approach, i.e., address 
conditions affecting safe flight that we know can happen--before they 
happen. This approach would require persons to analyze the causes of 
WFD in relation to the entire airplane and to analyze repairs, 
alterations, and modifications installed on the airplane.
    Based on the ARAC recommendations \4\ and our own analysis, we have 
determined that operators, TC holders, and STC holders need to place 
more emphasis on WFD. This proposal is designed to heighten the 
awareness of the threat of WFD to airplanes and to change the current 
approach to maintaining and modifying them. Table 2 summarizes the 
proposed regulatory changes discussed today.
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    \4\ ``Structural Fatigue Evaluation for Aging Airplanes'' 
(October, 1993); recommendation to add an appendix to AC 91-56, 
``Supplemental Structural Inspection Program (SSIP) for Large 
Transport Category Airplanes''; ``Recommendations for Regulatory 
Action to Prevent Widespread Fatigue Damage in the Commercial 
Fleet'' Rev. A (June, 1999); ``General Structures Harmonization 
Working Group Report Damage Tolerance and Fatigue Evaluation of 
Structures FAR/JAR Sec.  25.571'' (October, 2003).

                         Table 2.--Summary of Proposed Regulatory Changes Addressing WFD
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                14 CFR                 Description of proposal         Applies to            Compliance date
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Sec.   25.571........................  Replace ``design         Future applicants for    Before approval of TC
                                        service goal'' with      new Type Certificates    by Aircraft
                                        ``initial operational    (TC).                    Certification Office
                                        limit.''                                          (ACO).
                                       Require an initial
                                        operational limit as
                                        part of the
                                        Airworthiness
                                        Limitation Section
                                        (ALS) of the
                                        Instructions for
                                        Continued
                                        Airworthiness (ICA).
Sec.   25.1807.......................  Require initial          TC holders.............  December 18, 2007.
                                        operational limits for  Supplemental TC (STC)    December 18, 2007.
                                        all transport category   holders*.               Later of December 18,
                                        airplanes with a        Applicants for pending    2007, or date of
                                        Maximum Take-off Gross   TCs and STCs.*.          certificate.
                                        Weight (MTGW) greater   Applicants for new       Later of December 18,
                                        75,000 lb.               STCs* and amended        2007, or date of
                                                                 TCs.*.                   certificate.
                                       Establish WFD            TC holders.............  December 18, 2009.
                                        guidelines for          Applicants for TCs.....  Later of December 18,
                                        assessing repairs,                                2009, or date of
                                        alterations, and                                  certificate.
                                        modifications.
Sec.   25.1809.......................  Require WFD assessment   STC holders (other than  December 18, 2010.
                                        of all existing,         those covered by Sec.   Later of December 18,
                                        pending, and future       25.1807).               2010, or date of
                                        structural design       Applicants for pending    certificate.
                                        changes in               and future STCs and
                                        relationship to          amended TCs.
                                        initial operational
                                        limits; require
                                        development of any
                                        maintenance actions to
                                        preclude WFD.
Sec.   25.1811.......................   Establish requirements  Any person.............  Before approval of
                                        for extending any                                 extension by ACO.
                                        operational limits.
Sec.   25.1813.......................  Establish requirements   Any person seeking       Before approval of
                                        for evaluating certain   approval for repairs,    repairs, alterations,
                                        repairs, alterations,    alterations, or          or modifications by
                                        and modifications        modifications.           ACO.
                                        proposed for
                                        installation on
                                        airplanes with an
                                        extended operational
                                        limit.
Appendix H to part 25................  Require initial          Applicants for future    Before approval of TC
                                        operational limits as    TCs.                     by ACO.
                                        part of the ALS of the
                                        ICA.
                                       Require guidelines for
                                        evaluating WFD effects
                                        of repairs,
                                        alterations, and
                                        modifications.
Sec.   121.1115 Sec.   129.115.......  Require operators to     U.S. certificate         June 18, 2008.
                                        incorporate              holders and foreign
                                        operational limits       persons operating U.S.-
                                        into their maintenance   registered transport
                                        programs.                category airplanes.
                                       Require operators to     .......................  Before operating under
                                        incorporate any WFD                               extended operational
                                        airworthiness                                     limit.
                                        limitations for
                                        airplanes with
                                        extended operational
                                        limits.

[[Page 19932]]

 
                                       Establish requirements   .......................  Within 90 days after
                                        for identification and                            return to service,
                                        evaluation of certain                             following repairs,
                                        repairs, alterations,                             alterations, or
                                        and modifications                                 modifications.
                                        installed on airplanes
                                        operating under an
                                        extended operational
                                        limit.
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* Where STC increases MTGW to greater than 75,000 lb.
Note. There are also requirements for current holders of design approvals and those with pending design
  approvals to develop compliance plans, detailing how they will achieve compliance with the applicable
  requirements. For future applicants, similar information would be contained in a certification plan. To
  simplify the table above, these administrative requirements were omitted.

III. Requirements for Design Approval Holders

A. Ongoing Responsibility of Type Certificate Holders for Continued 
Airworthiness

    Several recent safety regulations necessitated action by air 
carriers and other operators but did not require design approval 
holders to develop and provide the necessary data and documents to 
facilitate the operators' compliance. Operators are often dependent on 
action by a design approval holder before they can implement new safety 
rules. Ongoing difficulty reported by operators in attempting to meet 
these rules has convinced us that corresponding design approval holder 
(DAH) responsibilities may be warranted under certain circumstances to 
enable operators to meet regulatory deadlines. When DAHs fail to 
provide the required data in a timely manner, operators may be forced 
to incur the costs associated with obtaining the expertise to develop 
the data. Some examples of programs in which some DAHs did not develop 
and make available the necessary information in a timely manner 
include:
     Thrust reversers, where it took 10 years to develop some 
service information AD-related items;
     Class D to Class C Cargo Conversions, where one TC holder 
did not develop the necessary modifications in time to support operator 
compliance and where several operators were unable to obtain timely 
technical support and modification parts from STC holders;
     The Reinforced Flight Deck Door Program, where most 
operators had substantially less than the one-year compliance time 
originally anticipated because of delays in developing and certifying 
the new designs;
     Repair Assessment Rule, where some operators were required 
to develop their own data for FAA approval in order to meet the rule's 
compliance date; and
     Structural Repair Manuals, where operators are still 
awaiting DAH action to perform damage tolerance evaluations and 
establish inspections, even though the DAH committed to completing this 
activity by 1993.
    In addition, DAHs have committed in the past to providing data to 
the FAA to support the certification basis of an airplane. In some 
instances, the DAH has missed the due date given for this commitment by 
up to 13 years.
    We intend to require type-certificate holders, manufacturers and 
others to take actions necessary to support the continued airworthiness 
of and to improve the safety of transport category airplanes. Such 
actions include performing assessments, developing design changes, 
revising ICAs, and making available necessary documentation to affected 
persons. We believe this requirement is necessary to facilitate 
compliance by air carriers with operating rules that in effect demand 
the use of new safety features.
    To address this problem, we propose to amend subpart A of part 25 
to expand its coverage and to add a new subpart I to establish 
requirements for current holders. As discussed in our final rule, 
``Fuel Tank Safety Compliance Extension and Aging Airplane Program 
Update'' (69 FR 45936, July 30, 2004), this and related proposals would 
add provisions to a new subpart I requiring actions by design approval 
holders that will allow operators to comply with our rules.
    Part 25 currently sets airworthiness standards for the issuance of 
TCs and changes to those certificates for transport category airplanes. 
It does not list the specific responsibilities of manufacturers to 
ensure continued airworthiness of these airplanes once the certificate 
is issued. Therefore, we propose to revise Sec.  25.1 by adding 
paragraph (c) to make clear that part 25 creates such responsibilities 
for holders of existing type and supplemental type certificates for 
transport category airplanes and applicants for approval of design 
changes to those certificates. Paragraph (d) would be added to make 
part 25 applicable to persons seeking approval of repairs, alterations, 
or modifications of certain transport category airplanes. This latter 
category is included, because repairs, alterations, and modifications 
can affect the structural integrity of the airplane. These changes may 
have an adverse effect on the continued airworthiness of the airplane. 
Those seeking approval of these changes should be aware of these 
effects and address these issues if relevant.
    In order to ensure the effectiveness of this change, we would also 
amend Sec.  25.2(d) (``Special retroactive requirements'') so as to 
require adherence to a new Subpart I which may require design changes 
and other activities by manufacturers when needed. The amended 
paragraph would also apply to persons seeking approval of repairs, 
alterations or modifications of transport category airplanes. This 
latter category is included because repairs, alterations and 
modifications can affect the structural integrity of the airplane. If 
the repairs, modifications or alterations are performed incorrectly, 
they may have an adverse effect on the continued airworthiness of the 
airplane.
    This proposal would establish a new subpart I, Continued 
Airworthiness and Safety Improvements, where we would locate rules 
imposing ongoing responsibilities on design approval holders. On July 
12, 2005, we issued policy statement PS-ANM110-7-12-2005, ``Safety--A 
Shared Responsibility--New Direction for Addressing Airworthiness 
Issues for Transport Airplanes'' (70 FR 40166). The policy states, in 
part, ``Based on our evaluation of more effective regulatory approaches 
for certain types of safety initiatives and the comments received from 
the Aging Airplane Program Update (July 30, 2004), the FAA has 
concluded that we need to adopt a regulatory approach recognizing the 
shared responsibility between design approval holders (DAHs) and 
operators. When we decide that general

[[Page 19933]]

rulemaking is needed to address an airworthiness issue, and believe the 
safety objective can only be fully achieved if the DAHs provide 
operators with the necessary information in a timely manner, we will 
propose requirements for the affected DAHs to provide that information 
by a certain date.''
    We believe that the safety objectives contained in this proposal 
can only be reliably achieved and acceptable to the FAA if the DAHs 
provide the operators with the initial operational limits required by 
the proposed operational rules for parts 121 and 129. Our determination 
that DAH requirements are necessary to support the initiatives 
contained in this proposal is based on several factors:
     Developing initial operational limits is complex. Only the 
airplane manufacturer, or DAH, has access to all the necessary type 
design data needed for the timely and efficient development of the 
required initial operational limit.
     FAA-approved operational limits need to be available in a 
timely manner. Due to the complexity of these initial operational 
limits, we need to ensure that the DAHs submit them for approval on 
schedule. This will allow the FAA Oversight Office having approval 
authority to ensure that the initial operational limits are acceptable, 
are available on time, and can be readily implemented by the affected 
operators.
     The proposals in this NPRM affect a large number of 
different types of transport airplanes. Because the safety issues 
addressed by this proposal are common to many airplanes, we need to 
ensure that technical requirements are met consistently and the 
processes of compliance are consistent. This will ensure that the 
proposed safety enhancements are implemented in a standardized manner.
     The safety objectives of this proposal need to be 
maintained for the operational life of the airplane. We need to ensure 
that future design changes to the type design of the airplane do not 
degrade the safety enhancements achieved by the incorporation of 
initial operational limits. We need to be aware of future changes to 
the type designs to ensure that these changes do not invalidate initial 
operational limits developed under the requirements of this proposal.
    Based on the above reasons and the stated safety objectives of FAA 
policy PS-ANM110-7-12-2005, we are proposing to implement DAH 
requirements applicable to operational limits.
    In the past, this type of requirement took the form of a Special 
Federal Aviation Regulations (SFAR). These regulations are difficult to 
locate because they are scattered throughout Title 14. Placing all 
these types of requirements in a single subpart of part 25 which 
contains the airworthiness standards for transport category airplanes 
would provide ready access to critical rules.
    In preliminary discussions with foreign aviation authorities with 
whom we try to harmonize our safety rules, they have expressed concern 
about consolidating parallel requirements in their counterparts to part 
25. They have suggested that it may be more appropriate to place them 
in part 21 or elsewhere. Therefore, we specifically request comments 
from the public, including foreign authorities, on the appropriate 
place for these airworthiness requirements for type certificate 
holders.
    We reserve additional sections in this proposed subpart to include 
other future aging airplane rules, several of which are under 
development. Some of these proposals include similar language 
establishing the general airworthiness responsibilities of 
manufacturers and thus include some overlapping provisions. Once any 
proposal establishing these broad responsibilities becomes a final 
rule, we will delete the duplicative requirements from the other 
proposals and retain only that language pertinent to any specific new 
safety regulations (such as fuel-tank flammability reduction).
    However, the ongoing-airworthiness requirements in Subpart I would 
not by their terms reach applicants for TCs with respect to new 
projects for which application is made after the effective date of the 
proposed rule. This is unnecessary, because when we adopt a new 
requirement for TC holders, there will be a corresponding amendment to 
part 25 expressly making the new, or a similar safety standard a 
condition for receiving a TC in the future. For example, in this 
proposal, the new requirements of Sec.  25.571 regarding WFD will 
govern future applications.
    For safety reasons, however, we are requiring that any application 
for a type design change not degrade the level of safety already 
created by the TC holder's presumed compliance with the subpart I rule. 
Currently, when reviewing an application for such a change, we employ 
the governing standards stated in part 21, specifically Sec.  21.101. 
That section generally requires compliance with standards in effect on 
the date of application but contains exceptions that may allow 
applicants to show compliance with earlier standards. For example, if a 
change is not considered ``significant,'' the applicant may be allowed 
to show compliance by pointing to standards that applied to the 
original TC. (See AC 21.101-1, ``Establishing the Certification Basis 
of Changed Aeronautical Products,'' a copy of which can be downloaded 
from https://www.airweb.faa.gov/rgl).
    With the adoption of subpart I rules, we must ensure that safety 
improvements that result from TC holder compliance with these 
requirements are not undone by later modifications. Therefore, even 
when we determine under Sec.  21.101 that applicants need not comply 
with the latest airworthiness standards, they will be required to 
demonstrate that the change would not degrade the level of safety 
provided by the TC holder's compliance with the subpart I rule. In the 
context of this proposal, for example, this will mean that an applicant 
for approval of a design change would have to perform a WFD evaluation 
to determine if any maintenance actions are necessary to preclude WFD.

B. Applicability

1. Holders of Type Certificates and Supplemental Type Certificates
    This proposal, if adopted, would impose requirements on TC holders 
for all large transport category airplanes. Under Sec.  25.571, an 
applicant for a TC would have to establish an initial operational limit 
for the contemplated airplane design as part of its application. 
Likewise, existing TC holders would have to establish an initial 
operational limit for all large transport category airplanes under 
Sec.  25.1807 if the MTGW of the airplane exceeds 75,000 lb. Type 
certificate and STC holders would also have to establish an initial 
operational limit for all large transport category airplanes under 
Sec.  25.1807 if the MTGW of the airplane was 75,000 pounds or less, 
and later increased to greater than 75,000 pounds by an amended type 
certificate or supplemental type certificate.
    This proposal, if adopted, would apply not only to domestic TC and 
STC holders, but also to foreign TC and STC holders. This rule would be 
different from most type certification programs for new TCs, where 
foreign applicants typically work with their responsible certification 
authority and the FAA relies to some degree upon that authority's 
findings of compliance under bilateral airworthiness agreements. 
Presently no other certification authority has adopted requirements 
addressing WFD for existing TCs. Additionally, while some

[[Page 19934]]

authorities have indicated an interest in adopting some type of 
requirements for new airplane designs, they may not adopt requirements 
applicable to existing TCs.
    Accordingly, the FAA will retain the authority to make all the 
necessary compliance determinations and, where appropriate, may request 
certain compliance determinations by the appropriate foreign 
authorities using procedures developed under the bilateral agreements. 
The compliance planning provisions of this proposed rule are equally 
important for domestic and foreign TC and STC holders and applicants, 
and we will work with the foreign authorities to ensure that their TC 
and STC holders and applicants perform the planning necessary to comply 
with those requirements.
2. Airplanes
    If adopted, this rule would apply, with some exceptions discussed 
below, to large transport category airplane designs (MTGW greater than 
75,000 pounds) by virtue of either the original certification of the 
airplane or a later increase in its MTGW. All transport category 
airplanes certificated under a TC that was applied for after the 
effective date of the final rule would also be subject to the 
requirements proposed today. This combined approach would result in the 
coverage of airplanes where the safety benefits and the public interest 
are the greatest.
    The ARAC working group that developed this recommendation did not 
include design approval holders for airplanes of less than 75,000 
pounds MTGW, in part because they were not asked to do so. However, in 
addition to its WFD recommendations, this working group developed 
recommendations on other aging airplane issues, including the 
Supplemental Structural Inspection Program, the Corrosion Prevention 
and Control Program, the Repair Assessment Program, and the Mandatory 
Modification Program. Because of these efforts, design approval holders 
for large transport category airplanes have already developed the 
technology and the internal organizational capability to address WFD. 
Therefore, the 75,000 pound MTGW is a logical reference point for 
developing programs for addressing WFD.
    We considered applying this proposal to all existing part 25 
airplanes. However, we have determined that smaller regional jets do 
not currently present a risk of WFD sufficient to justify the cost 
associated with meeting this proposal.
    The 75,000-pound cutoff excludes about 1,600 regional jets that are 
operating under parts 121 and 129 today. Of those airplanes, there are 
approximately 430 regional jets that are at least eight years old. 
These airplanes have accumulated an average of 12,000 flight cycles. 
The regional jet with the greatest number of flight cycles is 11 years 
old and has accumulated about 26,000 flight cycles, well below the 
existing design service goal for this airplane of 60,000 flight cycles.
    The FAA recognizes that using a cutoff of 75,000 pounds does not 
align with the FAA's ``One Level of Safety'' initiative (that is, the 
same level for all airplanes used in air carrier service). However, we 
determined a cutoff of 75,000 pounds to be appropriate at this time for 
the following reasons:
     This is the same cutoff used for the four aging airplane 
programs mentioned above, and the affected type certificate holders are 
able to address these problems now.
     Some airplanes over 75,000 pounds are at a greater risk 
due to higher total cycles and age.
     Most air carrier airplanes are of this size, and many of 
them are near or over their design service goal.
     The regional jets not affected are relatively young and, 
therefore, at low risk relative to WFD.
     The high-cycle regional jet will be in service for an 
additional 14 years before reaching its design service goal.
    The FAA may determine that we need to expand the scope of this rule 
at a later time, based on evaluations of the potential for WFD in 
regional jets. All of these regional jets are manufactured in other 
countries, and any efforts to address WFD should be developed in 
coordination with those countries. Until that time, if WFD problems are 
identified in these airplanes, we will address them through 
airworthiness directives. No WFD problems have yet been identified for 
regional jets. The FAA requests comments on this aspect of the proposed 
rule.
    While the ARAC recommendations applied to all transport category 
airplanes over 75,000 pounds, the group of airplanes of most concern is 
that group operating under parts 121 and 129. Because carriers in 
scheduled operations fly airplanes operated under those parts, they are 
flown more often than other airplanes of comparable size and are 
accordingly more likely to develop WFD. Thus, this proposal would 
exclude airplanes over 75,000 pounds that are not operated under parts 
121 or 129. For this reason, we have tentatively decided that this 
proposal, if adopted, should exclude the Bombardier BD-700, the 
Gulfstream G-V, the Gulfstream G-VSP, and the British Aerospace, 
Aircraft Group and Societe Nationale Industrielle Aerospatiale Concorde 
Type 1.
    It is not clear at this time that the possible benefits of this 
rule for those airplanes would be proportionate to the cost involved. 
We request comments on the feasibility and benefits of including or 
excluding these airplanes. We also request comments on the feasibility 
of including or excluding any other transport category airplanes with a 
maximum takeoff gross weight greater than 75,000 pounds from the 
requirements of this provision, whether or not they are operated under 
parts 121 and 129.

C. Initial Operational Limit (Sec.  25.571, Sec.  25.1807)

    Under this proposal, design approval holders would be required to 
establish an initial operational limit \5\ for all transport airplanes 
if certificated under a new TC and for those transport airplanes over 
75,000 pounds if certificated under an existing TC. Demonstration that 
WFD will not occur prior to the initial operational limit typically 
would involve an evaluation of the airplane model using fatigue test 
evidence, analyses, and airplane service information. Initial 
operational limits may also include specified maintenance actions 
necessary to preclude WFD, which would be addressed through the 
airworthiness directive process.\6\
---------------------------------------------------------------------------

    \5\ The most direct method for limiting the operation of an 
airplane is to prohibit operation beyond a certain point. For the 
purpose of this rule, we are using the term ``operational limit of 
an airplane'' rather than ``limit of valdity of the maintenance 
program'' as recommended by ARAC.
    \6\ We intend to use the AD process, so that operators will have 
an opportunity to comment on the contemplated maintenance actions.
---------------------------------------------------------------------------

    Airplane owners or operators may need to take certain maintenance 
actions to support the operational limits. These actions may include 
additional inspections, structural modifications, or replacements. The 
inspections would include an inspection start point and repetitive 
inspection intervals, along with inspection methods. Because 
inspections may not be reliable in detecting MSD or MED, structural 
modification points, which may include modifications or replacements, 
may eventually be required. Means of compliance with the requirements 
for performing a WFD evaluation and establishing an inspection start 
point and structural modification points will be further described in a 
proposed AC.
    To establish an initial operational limit, the FAA recognizes that 
the structural configuration of the airplane

[[Page 19935]]

needs to be identified. Thus, Sec.  25.1807 would specify the airplane 
structural configurations that must be evaluated. As a minimum, the 
structural configuration would consist of all model variations and 
derivatives approved under the type certificate and all structural 
modifications and replacements mandated by ADs as of the effective date 
of the rule. These ADs would only be those issued against any 
configurations developed by TC holders. They would not be for any ADs 
issued against modifications defined by an STC installed on affected 
airplanes. The result would be an airplane structural configuration 
that is clearly understood by both industry and the FAA.
    The initial operational limit would be stated as a number of total 
accumulated flight cycles or flight hours. An initial operational limit 
based on flight hours may be required for structure, such as the wings, 
that typically accumulates fatigue damage due to the repeated flight 
loads that occur on an airplane over time. An initial operational limit 
based on flight cycles may be required for structure, such as the 
fuselage, that typically accumulates fatigue damage due to the 
pressurization and depressurization of an airplane. There is no way to 
correlate between the two limits without knowing the applicable design 
and operational variables, such as average flight length. Accordingly, 
design approval holders may need to establish both a flight hour limit 
and a flight cycle limit.
    The initial evaluation of the airplane structural configuration 
should identify a projected airplane usage beyond its design service 
goal (DSG). This projected airplane usage is also known as the 
``proposed extended service goal'' (ESG). Typically, an evaluation 
through at least an additional twenty-five percent of the DSG would 
provide a realistic ESG. The ESG would be based on an additional 
evaluation of the airplane structural configuration and depends on the 
following:
     The projected useful life of the airplane at the time of 
the initial evaluation;
     Current inspection techniques and procedures; and
     Airline advance planning requirements for introduction of 
new maintenance actions, to support the ESG.
    Design approval holders may select DSGs or ESGs as starting points 
for establishing initial operational limits. Service information may be 
available for design approval holders to make those initial operational 
limits higher. In fact, the FAA is aware that design approval holders 
may have service information, such as service bulletins or all operator 
letters that could have an impact on proposed initial operational 
limits, but have not been mandated by AD. We are also aware that these 
persons may be in the process of developing service information that 
could have an impact on proposed initial operational limits. They may 
choose to specify additional maintenance actions resulting from such 
service information that could result in higher initial operational 
limits.
    Accordingly, the proposed rule includes an option for design 
approval holders to use existing maintenance actions for which service 
information has not been mandated by AD. These maintenance actions 
would be in addition to the airplane structural configurations that 
design approval holders would evaluate under the proposed regulation. 
To use this option, the affected design approval holders would be 
required to submit a list identifying the existing maintenance actions 
to the FAA oversight office. The affected design approval holders would 
then establish initial operational limits based on WFD evaluations that 
take credit for existing maintenance actions.
    The proposed rule also includes an option for affected design 
approval holders to use maintenance actions for which service 
information has not been issued. Those maintenance actions would be in 
addition to the airplane structural configurations that must be 
evaluated. To use this option, the affected persons would be required 
to submit a list identifying each of those maintenance actions and a 
binding schedule for providing in a timely manner the necessary service 
information for those actions to the FAA oversight office. The binding 
schedule is necessary to ensure the applicable service information is 
provided to the FAA in sufficient time for the agency to issue ADs 
mandating these actions, and operators to comply with them before WFD 
occurs. The design approval holders would then establish initial 
operational limits based on WFD evaluations that take credit for 
maintenance actions for which service information has not been issued.
    The WFD evaluation would consist of identifying structure 
susceptible to multiple site damage or multiple element damage based on 
the configurations discussed above. Once the structure has been 
identified, affected design approval holders would determine when WFD 
is likely to occur. This WFD evaluation would be based on consideration 
of the following:
     Service history: reported findings of multiple site damage 
or multiple element damage.
     Test data: WFD information from past component or full-
scale test results. This could include information on susceptibility of 
structure to WFD, crack initiation life, crack growth life, and 
residual strength.
     Fatigue analyses: predictions of times when multiple site 
damage or multiple element damage cracking would occur.
     Damage tolerance analyses: predictions of multiple site 
damage or multiple element crack growth life and residual strength.
     Teardown inspections of high-usage airplanes.
    Certain design approval holders have revealed to the FAA their 
plans to establish initial operational limits that would be 130 to 150 
percent of the DSG or ESG for their airplanes. They have also started 
to identify the necessary maintenance actions, including the inspection 
and modification start points, to preclude WFD up to the established 
initial operational limits for these airplanes. Many inspection and 
modification start points would be approximately at the design service 
goal or, in some cases, at 125 percent of the design service goal. This 
would support an initial operational limit that could be substantially 
higher than the DSG or ESG for a particular airplane. Other design 
approval holders have indicated that the initial operational limits for 
their airplanes would be at DSG or ESG. This is because relatively few 
of their airplanes are in operation today or all of their airplanes are 
many years away from accumulating the number of flight cycles shown in 
Table 3.
    Table 3 provides estimates of DSGs and ESGs of various airplanes 
that would be affected by this proposal. These DSGs and ESGs are based 
on information provided by type certificate holders or on a 
conservative estimate by the FAA.

[[Page 19936]]



               Table 3.--Design and Extended Service Goals
------------------------------------------------------------------------
                                                           Service goals
         Airplane type              Type  certificate       (in flight
                                                              cycles)
------------------------------------------------------------------------
Airbus:
    A300 B2-1A, B2-1C and B2K-  A35EU...................          48,000
     3C.
    A300 B4-2C and B4-103.....  A35EU...................          40,000
    A300 Model B4-203.........  A35EU...................          34,000
    A300 B4-600 Series, B4-     A35EU...................          30,000
     600R Series and F4-600R
     Series.
    A310-200 Series...........  A35EU...................          40,000
    A310-300 Series...........  A35EU...................          35,000
    A319 (all models).........  A28NM...................          48,000
    A320 (all models).........  A28NM...................          48,000
    A321 (all models).........  A28NM...................          48,000
    A330 (all models).........  A46NM...................          40,000
    A340 (all models).........  A43NM...................          20,000
------------------------------------------------------------------------
Boeing:
    Boeing 707 (-100 series     4A21....................          20,000
     and -200 series).
    Boeing 707 (-300 series     4A26....................          20,000
     and -400 series).
    Boeing 717 (all models)...  A6WE....................          60,000
    Boeing 720................  4A28....................          30,000
    Boeing 727................  A3WE....................          60,000
    Boeing 737................  A16WE...................          75,000
    Boeing 747................  A20WE...................          20,000
    Boeing 757................  A2NM....................          50,000
    Boeing 767................  A1NM....................          50,000
    Boeing 777................  T00001SE................          44,000
------------------------------------------------------------------------
Bombardier Aerospace Model:
    CL-44D4 and CL-44J........  1A20....................          20,000
------------------------------------------------------------------------
British Aerospace Airbus,
 Ltd.:
    BAC 1-11 (all models).....  A5EU....................          85,000
British Aerospace (Commercial
 Aircraft) Ltd.:
    Armstrong Whitworth Argosy  7A9.....................          20,000
     A.W. 650 Series 101.
------------------------------------------------------------------------
BAE Systems (Operations) Ltd.:
    BAE 46 (all models) and     A49EU...................          50,000
     Avro 146.
    RJ70A, RJ85A and RJ100A
     (all models).
------------------------------------------------------------------------
Fokker:
    F28/F70/F100 (all models).  A20EU...................          90,000
------------------------------------------------------------------------
Lockheed:
    300-50A01 (USAF C 141A)...  A2SO....................          20,000
    L-1011 (all models).......  A23WE...................          36,000
    L188 (all models).........  A1SO....................          26,600
    382 (all models)..........  4A22....................          20,000
    1649A-98..................  4A17....................          20,000
    1049-54, 1049B-55, 1049C-   6A5.....................          20,000
     55, 1049D-55, 1049E-55,
     1049F-55, 1049G-82.
    49-46, 149-46, 649-79,      A-763...................          20,000
     649A-79, 749-79, 749A-79.
------------------------------------------------------------------------
McDonnell Douglas:
    DC-6......................  A-781...................          20,000
    DC-6A (all models)........  6A3.....................          20,000
    DC-6B (all models)........  6A4.....................