[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
