[Federal Register Volume 63, Number 196 (Friday, October 9, 1998)]
[Proposed Rules]
[Pages 54391-54393]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-27124]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 98-NM-58-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737-100, -200, -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 737-100, -
200, -300, -400, and -500 series airplanes. This proposal would require 
repetitive inspections to detect cracking of various areas of the 
forward pressure bulkhead, and repair, if necessary. This proposal 
would also require certain preventive modifications, which, when 
accomplished, would terminate the repetitive inspections for most, but 
not all, of the affected areas. This proposal is prompted by reports 
indicating that numerous fatigue cracks were found on critical areas of 
the forward pressure bulkhead. The actions specified by the proposed AD 
are intended to prevent such fatigue cracking, which could result in 
rapid decompression of the airplane fuselage.

DATES: Comments must be received by November 23, 1998.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 98-NM-58-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.
    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; or at the Office of the Federal Register, 800 North Capitol 
Street, NW., suite 700, Washington, DC.

FOR FURTHER INFORMATION CONTACT: Nenita K. Odesa, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA, Transport Airplane Directorate, 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.
    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 98-NM-58-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. 98-NM-58-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

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.

[[Page 54392]]

Explanation of Relevant Service Information

    The FAA has reviewed and approved Boeing Alert Service Bulletin 
737-53A1173, Revision 2, dated January 15, 1998, which describes 
procedures for repetitive inspections to detect cracking of the body 
station 178 forward pressure bulkhead; and repair, if necessary. The 
service bulletin lists several types of inspections to be performed on 
the side chord areas, vertical chords, and center web area of the 
bulkhead. The inspections applicable to these areas consist of detailed 
visual/borescope inspections, eddy current inspections, and ultrasonic 
inspections.
    The alert service bulletin also describes procedures for certain 
preventive modifications, which, if accomplished, would eliminate the 
need for repetitive inspections of most, but not all, of the affected 
areas. Specifically, these modifications consist of replacing portions 
of the bulkhead center web area and installing certain angles and 
straps to strengthen the side and vertical chord areas.

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 alert service bulletin described previously, except as discussed 
below.

Differences Between Proposed Rule and Alert Service Bulletin

    Operators should note that, although the alert service bulletin 
specifies that the manufacturer may be contacted for disposition of 
certain repair conditions, this proposal would require that the repair 
of those conditions be accomplished in accordance with a method 
approved by the FAA.
    Operators should also note that, although the alert service 
bulletin recommends accomplishing the initial inspections prior to the 
accumulation of 20,000 total flight cycles (after the release of the 
alert service bulletin), followed by repetitive inspections every 6,000 
flight cycles, the FAA has determined that this would not address the 
identified unsafe condition in a timely manner. In developing an 
appropriate compliance time for this AD, 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.
    In light of all of these factors, the FAA finds that an earlier 
compliance time (i.e., a threshold for initial inspections of 15,000 
total flight cycles, and a repetitive interval of 3,000 flight cycles, 
for airplanes that have accumulated less than 60,000 total flight 
cycles as of the effective date of this AD) for initiating the proposed 
inspections is warranted, in that it represents an appropriate interval 
of time allowable for affected airplanes to continue to operate without 
compromising safety. Additionally, for airplanes that have accumulated 
60,000 or more total flight cycles as of the effective date of this AD 
(i.e., those airplanes most susceptible to fatigue cracking) the 
proposed initial inspection threshold and repetitive inspection 
interval are 1,500 flight cycles after the effective date of this AD, 
and 3,000 flight cycles, respectively.
    Additionally, 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 for most, but not all, of the affected 
areas. The one structural location for which inspections would still be 
required is the side chord areas at water line 207, as the manufacturer 
has not yet developed a preventive modification for this location.

Interim Action

    This is considered to be interim action. The manufacturer has 
advised that it is developing a preventive modification for the side 
chord areas at water line 207 that will positively address the unsafe 
condition at this location. Once this modification is developed, 
approved, and available, the FAA may consider additional rulemaking.

Cost Impact

    There are approximately 2,802 airplanes of the affected design in 
the worldwide fleet. The FAA estimates that 1,130 airplanes of U.S. 
registry would be affected by this proposed AD.
    It would take approximately 380 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 
inspections proposed by this AD on U.S. operators is estimated to be 
$25,764,000, or $22,800 per airplane, per inspection cycle.
    It would take approximately 794 work hours per airplane to 
accomplish the preventive modifications, at an average labor rate of 
$60 per work hour. Required parts would cost approximately $15,000 per 
airplane. Based on these figures, the cost impact of the preventive 
modifications proposed by this AD on U.S. operators is estimated to be 
$70,783,200, or $62,640 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 AD were not adopted.

Regulatory Impact

    The regulations proposed herein would not have substantial direct 
effects on the States, on the relationship between the national 
government and the States, or on the distribution of power and 
responsibilities among the various levels of government. Therefore, in 
accordance with Executive Order 12612, it is determined that this 
proposal would not have sufficient federalism implications to warrant 
the preparation of a Federalism Assessment.
    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

[[Page 54393]]

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 98-NM-58-AD.

    Applicability: Model 737-100, -200, -300, -400, and -500 series 
airplanes; as listed in Boeing Alert Service Bulletin 737-57A1173, 
Revision 2, dated January 15, 1998; 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 (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 prevent fatigue cracking of the forward pressure bulkhead, 
which could result in rapid decompression of the airplane fuselage, 
accomplish the following:
    (a) Perform inspections of the center web, vertical chords, and 
side chord areas of the forward pressure bulkhead for fatigue 
cracking, in accordance with the Accomplishment Instructions of 
Boeing Alert Service Bulletin 737-53A1173, Revision 2, dated January 
15, 1998, at the time specified in paragraph (a)(1) or (a)(2) of 
this AD, as applicable. Thereafter, repeat the inspections at 
intervals not to exceed 3,000 flight cycles until the preventive 
modifications required by paragraph (d) of this AD have been 
accomplished.
    (1) For airplanes that have accumulated 60,000 or more total 
flight cycles as of the effective date of this AD: Inspect within 
1,500 flight cycles after the effective date of this AD.
    (2) For airplanes that have accumulated fewer than 60,000 total 
flight cycles as of the effective date of this AD: Inspect prior to 
the accumulation of 15,000 total flight cycles, or within 3,000 
flight cycles after the effective date of this AD, whichever occurs 
later.
    (b) If any crack is found during any inspection required by 
paragraph (a) of this AD, prior to further flight, repair the area 
in accordance with the Accomplishment Instructions of Boeing Alert 
Service Bulletin 737-53A1173, Revision 2, dated January 15, 1998; 
except, where the alert service bulletin specifies that the 
manufacturer may be contacted for repair instructions, repair in 
accordance with a method approved by the Manager, Seattle Aircraft 
Certification Office (ACO), FAA, Transport Airplane Directorate.
    (c) 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: Accomplish preventive modifications of the 
center web, vertical chords, and side chord areas of the forward 
pressure bulkhead, in accordance with the Accomplishment 
Instructions of Boeing Alert Service Bulletin 737-53A1173, Revision 
2, dated January 15, 1998. Accomplishment of these modifications 
constitutes terminating action for the inspections required by 
paragraph (a) of this AD, except for the requirement to inspect the 
side chord areas at water line 207 (for which no preventive 
modification is described in the alert service bulletin). For these 
side chord areas, continue inspecting in accordance with the 
requirements of paragraph (a) of this AD.
    (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 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 2: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

    (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 September 25, 1998.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 98-27124 Filed 10-8-98; 8:45 am]
BILLING CODE 4910-13-U