[Federal Register Volume 65, Number 202 (Wednesday, October 18, 2000)]
[Proposed Rules]
[Pages 62313-62315]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 00-26711]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 99-NM-380-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737-300, -400, and -500 
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 737-300, -
400, and -500 series airplanes. This proposal would require repetitive 
inspections to detect cracking of certain areas of the forward pressure 
bulkhead, and repair, if necessary. This proposal also would require 
certain preventive modifications, which, when accomplished, would 
terminate the repetitive inspections for the affected areas. This 
action is necessary to prevent fatigue cracking on critical areas of 
the forward pressure bulkhead, which could result in rapid 
decompression of the airplane fuselage. This action is intended to 
address the identified unsafe condition.

DATES: Comments must be received by December 4, 2000.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 99-NM-380-AD, 1601 Lind Avenue, SW., 
Renton, Washington 98055-4056. Comments may be inspected at this 
location between 9:00 a.m. and 3:00 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: 
<a href="/cdn-cgi/l/email-protection#be8793dfd0d393d0ceccd3ddd1d3d3dbd0cafed8dfdf90d9d1c8"><span class="__cf_email__" data-cfemail="bb8296dad5d696d5cbc9d6d8d4d6d6ded5cffbdddada95dcd4cd">[email protected]</span></a>. Comments sent via fax or the Internet must 
contain ``Docket No. 99-NM-380-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, 
Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, 
Washington.

FOR FURTHER INFORMATION CONTACT: Nenita K. Odesa, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 
1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 
227-2557; 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 notice may be changed in 
light of the comments received.
    Submit comments using the following format:
    <bullet> 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.
    <bullet> For each issue, state what specific change to the proposed 
AD is being requested.
    <bullet> 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 notice must submit a self-addressed, 
stamped postcard on which the following statement is made: ``Comments 
to Docket Number 99-NM-380-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. 99-NM-380-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

[[Page 62314]]

Discussion

    The FAA has received reports indicating that operators have found 
numerous fatigue cracks on the body station 178 forward pressure 
bulkhead on certain Boeing Model 737 series airplanes. The longest 
fatigue crack was approximately 25 inches in length. The fatigue cracks 
were found at three critical structural areas of the bulkhead, namely, 
at the side chord areas of the bulkhead, at certain vertical chords of 
the bulkhead; and on the bulkhead web itself between left and right 
buttock lines 17.0. Such fatigue cracking, if not corrected, could 
result in rapid decompression of the airplane fuselage.

Related Rulemaking

    On March 10, 2000, the FAA issued AD 2000-05-29, amendment 39-11639 
(65 FR 14834, March 20, 2000), applicable to certain Boeing Model 737-
100, -200, -300, -400, and -500 series airplanes, that requires 
repetitive inspections to detect cracking of various areas of the 
forward pressure bulkhead, and repair, if necessary. That action also 
provides for certain optional preventive modifications, which, if 
accomplished, would terminate the repetitive inspections for the 
affected areas. That action was prompted by reports indicating that 
numerous fatigue cracks were found on critical areas of the forward 
pressure bulkhead. The requirements of that AD are intended to prevent 
such fatigue cracking, which could result in rapid decompression of the 
airplane fuselage.
    In the preamble to AD 2000-05-29, the FAA specified that the 
actions required by that AD were considered interim action. The FAA 
indicated that it may consider further rulemaking action to mandate 
certain inspections and modifications to address fatigue cracking in 
the bulkhead of Model 737 series airplanes having line numbers 2738 
through 3071, inclusive. The FAA has determined that further rulemaking 
action is indeed necessary; this proposed AD follows from that 
determination.

Explanation of Relevant Service Information

    The FAA has reviewed and approved Boeing Alert Service Bulletin 
737-53A1208, dated May 6, 1999, which describes procedures for 
repetitive inspections to detect cracking of the vertical and side 
chord areas on the body station 178 forward pressure bulkhead; and 
repair, if necessary. The service bulletin lists several types of 
inspections to be performed on the vertical and side chord areas of the 
forward pressure bulkhead. The inspections applicable to these areas 
consist of detailed visual/borescope inspections, eddy current 
inspections, and ultrasonic inspections.
    The service bulletin also describes procedures for certain 
preventive modifications, which, if accomplished, would eliminate the 
need for the repetitive inspections. Specifically, these modifications 
consist of installing certain angles and straps to strengthen the 
vertical chord area at waterline 184, and the side chord area at 
waterline 207. 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 require accomplishment of the actions specified in 
the service bulletin described previously, except as discussed below.

Differences Between Proposed Rule and Alert Service Bulletin

    Operators should note that the alert service bulletin refers to 
certain preventive modifications as optional. However, this proposed AD 
would make these preventive modifications mandatory, and would require 
accomplishment prior to the accumulation of 75,000 total flight cycles 
or within 12,000 flight cycles after the effective date of this AD, 
whichever occurs later. The proposed grace period of 12,000 flight 
cycles was developed to correspond with a typical operator's heavy 
maintenance check schedule in order to minimize disruption to scheduled 
operations. As with the compliance times proposed for the inspections, 
the FAA considered not only the manufacturer's recommendation, but the 
degree of urgency associated with addressing the subject unsafe 
condition, the average utilization of the affected fleet, and the high 
number of airplanes that have already been found to be affected by the 
unsafe condition. These mandatory preventive modifications, when 
accomplished, would constitute terminating action for the repetitive 
inspection requirements of this proposed AD.

Cost Impact

    There are approximately 330 Model 737 series airplanes of the 
affected design in the worldwide fleet. The FAA estimates that 115 
airplanes of U.S. registry would be affected by this proposed AD.
    It would take approximately 2 work hours per airplane to accomplish 
the proposed inspection, 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 $13,800, or $120 per airplane, per 
inspection cycle.
    It would take approximately 38 work hours per airplane to 
accomplish the proposed modification of the vertical chords, at an 
average labor rate of $60 per work hour. Required parts would cost 
approximately $2,789 per airplane. Based on these figures, the cost 
impact of the proposed AD on U.S. operators is estimated to be 
$582,935, or $5,069 per airplane.
    It would take approximately 274 work hours per airplane to 
accomplish the proposed modification of the side chord areas, at an 
average labor rate of $60 per work hour. Required parts would cost 
approximately $6,629 per airplane. Based on these figures, the cost 
impact of the proposed AD on U.S. operators is estimated to be 
$2,652,935, or $23,069 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

[[Page 62315]]

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 99-NM-380-AD. 

    Applicability: Model 737-300, -400, and -500 series airplanes, 
certificated in any category; as listed in Boeing Alert Service 
Bulletin 737-53A1208, dated May 6, 1999.

    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 (d) 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 detect fatigue cracking of the forward pressure bulkhead, 
which could result in rapid decompression of the airplane fuselage, 
accomplish the following:

Initial and Repetitive Inspections

    (a) Before the accumulation of 20,000 total flight cycles, or 
within 3,000 flight cycles after the effective date of this AD, 
whichever occurs later: Perform the applicable inspections of the 
vertical and side chord areas of the forward pressure bulkhead to 
detect cracking, in accordance with the Accomplishment Instructions 
of Boeing Alert Service Bulletin 737-53A1208, dated May 6, 1999. 
Thereafter, repeat the inspections at intervals not to exceed 6,000 
flight cycles until the preventive modifications required by 
paragraph (c) of this AD have been accomplished.

Repair

    (b) If any cracking is detected during any inspection required 
by paragraph (a) of this AD, before further flight, repair the area 
in accordance with the Accomplishment Instructions of Boeing Alert 
Service Bulletin 737-53A1208, dated May 6, 1999.

Terminating Action

    (c) Before the accumulation of 75,000 total flight cycles, or 
within 12,000 flight cycles after the effective date of this AD, 
whichever occurs later: Accomplish preventive modifications of the 
vertical and side chord areas of the forward pressure bulkhead, in 
accordance with the Accomplishment Instructions of Boeing Alert 
Service Bulletin 737-53A1208, dated May 6, 1999. Accomplishment of 
these modifications constitutes terminating action for the 
repetitive inspections required by paragraph (a) of this AD.

Alternative Methods of Compliance

    (d) 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 Aircraft Certification 
Office (ACO), FAA. 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 2: 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

    (e) 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 October 12, 2000.
Donald L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 00-26711 Filed 10-17-00; 8:45 am]
BILLING CODE 4910-13-P


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