[Federal Register Volume 66, Number 134 (Thursday, July 12, 2001)]
[Proposed Rules]
[Pages 36520-36523]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 01-17434]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 2000-NM-74-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737-200 and -200C Series 
Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the adoption of a new airworthiness 
directive (AD) that is applicable to certain Boeing Model 737-200 and -
200C series airplanes. This proposal would require repetitive 
inspections to find cracking of certain fuselage lap joint areas, and 
repair of any cracking found. This proposal also would require eventual 
modification of those areas, which would constitute terminating action 
for the repetitive inspections. This action is necessary to find and 
fix cracking of certain fuselage lap joint areas, which could result in 
rapid decompression of the airplane. This action is intended to address 
the identified unsafe condition.

DATES: Comments must be received by August 27, 2001.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 2000-NM-74-AD, 1601 Lind Avenue, SW., 
Renton, Washington 98055-4056. Comments may be inspected at this 
location between 9 a.m. and 3 p.m., Monday through Friday, except 
Federal holidays. Comments may be submitted via fax to (425) 227-1232. 
Comments may also be sent via the Internet using the following address: 
[email protected]. Comments sent via fax or the Internet must 
contain ``Docket No. 2000-NM-74-AD'' in the subject line and need not 
be submitted in triplicate. Comments sent via the Internet as attached 
electronic files must be formatted in Microsoft Word 97 for Windows or 
ASCII text.
    The service information referenced in the proposed rule may be 
obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, 
Washington 98124-2207. This information may be examined at the FAA, 
1601 Lind Avenue, SW., Renton, Washington.

FOR FURTHER INFORMATION CONTACT: Scott Fung, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 
1601 Lind Avenue, SW., Renton, Washington; telephone (425) 227-1221; 
fax (425) 227-1181.

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. Communications shall identify the Rules Docket number 
and be submitted in triplicate to the address specified above. All 
communications received on or before the closing date for comments, 
specified above, will be considered before taking action on the 
proposed rule. The proposals contained in this action may be changed in 
light of the comments received.
    Submit comments using the following format:
     Organize comments issue-by-issue. For example, discuss a 
request to change the compliance time and a request to change the 
service bulletin reference as two separate issues.
     For each issue, state what specific change to the proposed 
AD is being requested.
     Include justification (e.g., reasons or data) for each 
request.
    Comments are specifically invited on the overall regulatory, 
economic, environmental, and energy aspects of the proposed rule. All 
comments submitted 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 Rules Docket.
    Commenters wishing the FAA to acknowledge receipt of their comments 
submitted in response to this action must submit a self-addressed, 
stamped postcard on which the following statement is made: ``Comments 
to Docket Number 2000-NM-74-AD.'' The postcard will be date stamped and 
returned to the commenter.

Availability of NPRMs

    Any person may obtain a copy of this NPRM by submitting a request 
to the FAA, Transport Airplane Directorate, ANM-114, Attention: Rules 
Docket No. 2000-NM-74-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Structural Airworthiness of Aging Transport Category Airplanes

    On April 28, 1988, a Boeing Model 737 series airplane was involved 
in an accident in which a 15-foot long section

[[Page 36521]]

of fuselage structure peeled open during flight. In light of this, the 
FAA initiated an Aging Fleet Program. The objective of that program is 
to identify and implement procedures to ensure the continuing 
structural airworthiness of aging transport category airplanes.
    As part of the Aging Fleet Program, the airplane manufacturer 
conducted cyclic pressure (fatigue) tests to evaluate the performance 
of the various fuselage skin panel lap joint configurations. The 
fuselage skin panel joint consists of two adjacent panels that overlap 
each other longitudinally and are joined together by three rows of 
fasteners at the overlap (hence, lap joint). Cracks in the upper skin 
of the lap joint led to the structural failure that occurred in the 
1988 accident discussed previously. These lap joints, installed on 
early Model 737 series airplanes having line numbers 1 through 291, 
were modified by replacing the countersunk fasteners in the upper 
fastener row of the lap joint with protruding head fasteners to correct 
and prevent cracking in the upper skin of the lap joint. To date, no 
cracking has been detected in the lower fastener row of these 
(modified) lap joints.
    However, at some locations on these same airplanes, the lap joint 
has a different configuration that includes a doubler, and cracking has 
been found in the lower row of fasteners in the lower skin of these 
joints. This type of joint was used extensively on subsequent airplanes 
(line numbers 292 through 2565 inclusive) to improve the lap joint and 
to prevent cracks in the upper skin. In 1994, tests were conducted on 
lap joints that incorporate doublers; test results revealed cracks in 
the lower skin of this lap joint. The airplane manufacturer determined 
that these cracks were caused by increased stresses in this area due to 
the increased bending stresses associated with the installation of the 
doubler on the upper skin.
    In light of these test results, the manufacturer inspected this 
type of lap joint on five aging airplanes and detected a total of 273 
fatigue cracks. The use of eddy current inspection techniques was 
required as the cracks in the lower skin are not detectable visually 
due to the positioning of the lower skin between the upper skin and the 
circumferential tear strap. Many of these cracks were found to have 
occurred simultaneously at adjacent fastener hole locations in the 
lower skin of the fuselage lap joint.
    This type of cracking of the lap joint is known as multiple site 
damage (MSD). MSD is characterized by the simultaneous presence of 
fatigue cracks in the same structural element (such as the lower skin 
panel of the lap joint). Coalescence of cracks at adjacent fastener 
holes in the lower skin can lead to sudden fracture and failure of the 
lap joint, which could result in rapid decompression of the airplane 
due to the reduction in the residual strength of a lap joint in the 
presence of MSD. This reduction of the structural integrity of the 
fuselage may occur at loads significantly below those that would be 
expected for structure having a single large crack. The accident 
discussed previously has demonstrated dramatically that small cracks 
acting together can have a significant effect on the residual strength 
of the aircraft structure.

Related Rulemaking

    On October 21, 1997, the FAA issued AD 97-22-07, amendment 39-10179 
(62 FR 55732, October 28, 1997), applicable to Boeing Model 737 series 
airplanes, line numbers 292 through 2565 inclusive, which requires 
repetitive inspections to detect cracking of the lower skin at the 
lower row of fasteners in the lap joints of the fuselage that have this 
doubler, and repair of any cracking detected. That action also requires 
modification of the fuselage lap joints at stringers S10 and S14, 
located between body stations (BS) 360 and BS 540, and located between 
BS 727 and BS 908.

Public Meeting

    A joint Federal Aviation Administration (FAA) and Boeing meeting 
was held on July 25-27, 2000, to inform industry of the activity on 
Boeing Model 727 and 737 fuselage lap joints. Others in attendance were 
representatives from air carriers and repair stations, as well as 
Principal Maintenance Inspectors (PMI) from the FAA Flight Standards 
Service. The objective of the meeting was to provide an overview of the 
FAA rulemaking process; discuss the recommendations of Boeing Service 
Bulletins 727-53A0222 and 737-53A1177, including background 
information; standardize the 727 and 737 service bulletins, where 
possible; and discuss the impact that the recommended service bulletin 
modifications would have on industry.
    During the meetings, holders of certain supplemental type 
certificates presented information pertaining to service bulletin 
activity for those airplanes that have been modified from a passenger 
to an all-cargo configuration. The meeting accomplished the objective 
of exchanging information between the FAA, Boeing, and industry on 
various aspects of Boeing Models 727 and 737 fuselage lap joints, 
including compliance planning. As a result of the meeting, attendees 
recognized the importance of modifying certain lap joints before 
reaching the point of widespread fatigue damage. Suggestions to improve 
the service bulletins and clarify AD compliance issues were made by 
operators and PMIs, and have been incorporated into the service 
bulletins and the proposed ADs discussed below. In addition, minutes of 
the public meeting are retained in the docket.

Other Relevant Rulemaking

    At this time, the FAA is considering two other separate rulemaking 
actions to address the remaining potential unsafe conditions relating 
to the cracking of the lap joints of the fuselage. Those two other 
actions would address:
     Additional repetitive inspections to find cracking of the 
lower skin at the lower row of fasteners in the lap joints of the 
fuselage, and replacement of the preventive modification with an 
improved modification on Model 737 series airplanes, line numbers 292 
through 2565 inclusive. And
     Replacement of certain repairs with improved repairs in 
certain fuselage lap joints done per the procedures described in the 
structural repair manual (SRM); and a high frequency eddy current 
inspection to find cracking of the SRM repairs of the lower skin at the 
lower row of fasteners in the lap joints of the fuselage, and repair of 
any cracking found on Model 737 series airplanes, line numbers 292 
through 2565 inclusive.

Explanation of Relevant Service Information

    The FAA has reviewed and approved Boeing Service Bulletin 737-
53A1177, Revision 6, dated May 31, 2001, which describes, among other 
things, procedures for repetitive low frequency eddy current 
inspections to find cracking of the left and right stringer S-10 and S-
14 lap joint areas, between BS 360 and BS 540, and BS 727 and BS 908, 
and repair, if necessary. The service bulletin also describes 
procedures for the installation of a lap joint modification, which, 
when accomplished, would eliminate the need for the repetitive 
inspections. Accomplishment of the actions specified in the service 
bulletin is intended to adequately address the identified unsafe 
condition.

Explanation of Requirements of Proposed Rule

    Since an unsafe condition has been identified that is likely to 
exist or develop on other products of this same type design, the 
proposed AD would

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require repetitive inspections to find cracking of certain fuselage lap 
joint areas, and repair of any cracking found. The proposed AD also 
would require eventual modification of those areas, which would 
constitute terminating action for the repetitive inspections. The 
actions would be required to be accomplished per the service bulletin 
described previously, except as discussed below.

Differences Between Service Bulletin and Proposed Rule

    The FAA recognizes that the lap joint modification specified in 
this proposed AD would require jacking, shoring, removing interior 
components, and modifying certain lap joints, which would require 
taking the airplane out of service for as much as 22 days. This lengthy 
shop visit, as well as the relatively short compliance time required to 
accomplish this proposed AD, make it necessary for operators to engage 
in compliance planning to ensure that, when the deadline for compliance 
arrives, all of the required actions have been completed on all 
affected airplanes. Therefore, paragraph (d) of this proposed AD would 
require that operators submit to the FAA a compliance plan within 3 
months after the effective date of this AD. This will enable the FAA to 
verify that all operators will be able to meet the deadlines imposed by 
this proposed AD.
    Operators should note that, in light of the complexity of the 
service bulletin, three separate rulemaking actions are being issued to 
address the potential unsafe conditions relating to the cracking of the 
lap joints of the fuselage. This proposed rule will address only Model 
737-200 and -200C series airplanes having line numbers 1 through 291 
inclusive.
    Operators also should note that, although the service bulletin 
specifies that the manufacturer may be contacted for disposition of 
certain repair/modification conditions, this proposed AD requires the 
repair/modification of those conditions to be accomplished per a method 
approved by the FAA, or per data meeting the type certification basis 
of the airplane approved by a Boeing Company Designated Engineering 
Representative who has been authorized by the FAA to make such 
findings.

Cost Impact

    There are approximately 159 Model 737-200 and -200C series 
airplanes of the affected design in the worldwide fleet. The FAA 
estimates that 55 airplanes of U.S. registry (over 10 years) would be 
affected by this proposed AD.
    It would take approximately 16 work hours per airplane to 
accomplish the proposed inspections, at an average labor rate of $60 
per work hour. Based on these figures, the cost impact of the proposed 
AD on U.S. operators is estimated to be $52,800, or $960 per airplane, 
per inspection cycle.
    It would take approximately 75 work hours per airplane to 
accomplish the proposed modifications, at an average labor rate of $60 
per work hour. Required parts would cost approximately $1,500 per 
airplane. Based on these figures, the cost impact of the proposed AD on 
U.S. operators is estimated to be $330,000, or $6,000 per airplane.
    The compliance plan that is proposed in this AD action would take 
approximately 24 work hours per airplane to accomplish, at an average 
labor rate of $60 per work hour. Based on these figures, the cost 
impact of the compliance plan on U.S. operators is estimated to be 
$79,200, or $1,440 per airplane.
    The cost impact figures discussed above are based on assumptions 
that no operator has yet accomplished any of the proposed requirements 
of this AD action, and that no operator would accomplish those actions 
in the future if this proposed AD were not adopted. The cost impact 
figures discussed in AD rulemaking actions represent only the time 
necessary to perform the specific actions actually required by the AD. 
These figures typically do not include incidental costs, such as the 
time required to gain access and close up, planning time, or time 
necessitated by other administrative actions.

Regulatory Impact

    The regulations proposed herein would not have a substantial direct 
effect 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, it 
is determined that this proposal would not have federalism implications 
under Executive Order 13132.
    For the reasons discussed above, I certify that this proposed 
regulation (1) is not a ``significant regulatory action'' under 
Executive Order 12866; (2) is not a ``significant rule'' under the DOT 
Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); 
and (3) if promulgated, will not have a significant economic impact, 
positive or negative, on a substantial number of small entities under 
the criteria of the Regulatory Flexibility Act. A copy of the draft 
regulatory evaluation prepared for this action is contained in the 
Rules Docket. A copy of it may be obtained by contacting the Rules 
Docket at the location provided under the caption ADDRESSES.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation Administration proposes to amend 
part 39 of the Federal Aviation Regulations (14 CFR part 39) as 
follows:

PART 39--AIRWORTHINESS DIRECTIVES

    1. The authority citation for part 39 continues to read as follows:

    Authority: 49 U.S.C. 106(g), 40113, 44701.


Sec. 39.13  [Amended]

    2. Section 39.13 is amended by adding the following new 
airworthiness directive:

Boeing: Docket 2000-NM-74-AD.

    Applicability: Model 737-200 and -200C airplanes having line 
numbers 1 through 291 inclusive, certificated in any category.

    Note 1: This AD applies to each airplane identified in the 
preceding applicability provision, regardless of whether it has been 
modified, altered, or repaired in the area subject to the 
requirements of this AD. For airplanes that have been modified, 
altered, or repaired so that the performance of the requirements of 
this AD is affected, the owner/operator must request approval for an 
alternative method of compliance in accordance with paragraph (f) of 
this AD. The request should include an assessment of the effect of 
the modification, alteration, or repair on the unsafe condition 
addressed by this AD; and, if the unsafe condition has not been 
eliminated, the request should include specific proposed actions to 
address it.

    Compliance: Required as indicated, unless accomplished 
previously.
    To find and fix cracking of certain fuselage lap joint areas, 
which could result in rapid decompression of the airplane, 
accomplish the following:

Repetitive Low Frequency Eddy Current (LFEC) Inspections

    (a) Do an LFEC inspection to find cracking of the left and right 
stringers S-10 and S-14 lap joints of the fuselage, located between 
body station (BS) 727 and BS 747, per Figures 7 and 8 of the 
Accomplishment Instructions of Boeing Service Bulletin 737-53A1177, 
Revision 6, dated May 31, 2001; at the time specified in paragraph 
(a)(1) or (a)(2) of this AD, as applicable. Repeat the inspection 
after that at intervals not to exceed 1,200 flight cycles until 
accomplishment of the lap joint modification (repair) required by 
paragraph (e) of this AD.
    (1) For airplanes that have accumulated 70,000 or more total 
flight cycles as of the

[[Page 36523]]

effective date of this AD: At the later of the times specified in 
paragraphs (a)(1)(i) and (a)(1)(ii) of this AD.
    (i) Before the accumulation of 71,200 total flight cycles.
    (ii) Within 300 flight cycles after the effective date of this 
AD.
    (2) For airplanes that have accumulated 45,000 or more total 
flight cycles, but less than 70,000 total flight cycles as of the 
effective date of this AD: At the later of the times specified in 
paragraphs (a)(2)(i) and (a)(2)(ii) of this AD.
    (i) Before the accumulation of 50,000 total flight cycles.
    (ii) Within 1,200 flight cycles after the effective date of this 
AD.

Crack Repair

    (b) Except as provided by paragraph (c) of this AD: If any 
cracking is found during any inspection required by this AD, before 
further flight, repair per Part II (``Crack Repair'') of the 
Accomplishment Instructions of Boeing Service Bulletin 737-53A1177, 
Revision 6, dated May 31, 2001.
    (c) If any cracking is found during any inspection required by 
this AD, and Boeing Service Bulletin 737-53A1177, Revision 6, dated 
May 31, 2001, specifies to contact Boeing for repair instructions: 
Repair before further flight, per a method approved by the Manager, 
Seattle Aircraft Certification Office (ACO), FAA; or per data 
meeting the type certification basis of the airplane approved by a 
Boeing Company Designated Engineering Representative (DER) who has 
been authorized by the Manager, Seattle ACO, to make such findings. 
For a repair method to be approved by the Manager, Seattle ACO, as 
required by this paragraph, the approval letter must specifically 
reference this AD.

Compliance Plan

    (d) Within 3 months after the effective date of this AD, submit 
a plan to the FAA identifying a schedule for compliance with 
paragraph (e) of this AD. This schedule must include, for each of 
the operator's affected airplanes, the dates and maintenance events 
(e.g., letter checks) when the required actions will be 
accomplished. For the purposes of this paragraph, ``FAA'' means the 
Principal Maintenance Inspector (PMI) for operators that are 
assigned a PMI, or the cognizant Flight Standards District Office 
for other operators. Information collection requirements contained 
in this regulation have been approved by the Office of Management 
and Budget (OMB) under the provisions of the Paperwork Reduction Act 
of 1980 (44 U.S.C. 3501 et seq.) and have been assigned OMB Control 
Number 2120-0056.

    Note 2: Operators are not required to submit revisions to the 
compliance plan required by paragraph (d) of this AD to the FAA.

Lap Joint Modification (Repair)

    (e) Before the accumulation of 50,000 total flight cycles or 
within 5,000 flight cycles after the effective date of this AD, 
whichever comes later: Install the lap joint repair of the left and 
right stringer S-10 and S-14 lap joints of the fuselage, between BS 
727 and BS 747, per Part III (``Lap Joint Repair''), of the 
Accomplishment Instructions of Boeing Service Bulletin 737-53A1177, 
Revision 6, dated May 31, 2001. Installation of this repair ends the 
repetitive inspections of the repaired areas required by paragraph 
(a) of this AD.

Alternative Methods of Compliance

    (f) An alternative method of compliance or adjustment of the 
compliance time that provides an acceptable level of safety may be 
used if approved by the Manager, Seattle ACO. Operators shall submit 
their requests through an appropriate FAA Principal Maintenance 
Inspector, who may add comments and then send it to the Manager, 
Seattle ACO.

    Note 3: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

Special Flight Permit

    (g) Special flight permits may be issued in accordance with 
sections 21.197 and 21.199 of the Federal Aviation Regulations (14 
CFR 21.197 and 21.199) to operate the airplane to a location where 
the requirements of this AD can be accomplished.

    Issued in Renton, Washington, on July 6, 2001.
Vi L. Lipski,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 01-17434 Filed 7-11-01; 8:45 am]
BILLING CODE 4910-13-P