[Federal Register Volume 61, Number 223 (Monday, November 18, 1996)]
[Proposed Rules]
[Pages 58669-58671]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-29417]
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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39
[Docket No. 96-NM-71-AD]
RIN 2120-AA64
Airworthiness Directives; Boeing Model 747-200, -300, and -400
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 747-200, -
300, and -400 series airplanes. This proposal would require repetitive
inspections to detect cracking of the front spar web of the center
section of the wing, and repair, if necessary. This proposal is
prompted by reports of fatigue cracking found in the front spar web.
The actions specified by the proposed AD are intended to prevent the
leakage of fuel into the forward cargo bay, as a result of fatigue
cracking in the front spar web, which could result in a potential fire
hazard.
DATES: Comments must be received by December 30, 1996.
ADDRESSES: Submit comments in triplicate to the Federal Aviation
Administration (FAA), Transport Airplane Directorate, ANM-103,
Attention: Rules Docket No. 96-NM-71-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.
FOR FURTHER INFORMATION CONTACT: Tamara Dow, Aerospace Engineer,
Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office,
1601 Lind Avenue, SW., Renton, Washington; telephone (206) 227-2771;
fax (206) 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 96-NM-71-AD.'' The postcard will be date stamped and
returned to the commenter.
[[Page 58670]]
Availability of NPRMs
Any person may obtain a copy of this NPRM by submitting a request
to the FAA, Transport Airplane Directorate, ANM-103, Attention: Rules
Docket No. 96-NM-71-AD, 1601 Lind Avenue, SW., Renton, Washington
98055-4056.
Discussion
The FAA has received reports indicating that fatigue cracks have
been found on several Boeing Model 747-100 series airplanes in the
front spar web of the center section of the wing. Two operators
reported cracks at the tangent point of the pocket fillet radius
running vertically along the edge of the web stiffener. One crack was
found while troubleshooting a whistling sound in the cabin that
occurred during flight. These cracks were detected on airplanes that
had accumulated between 13,932 and 24,264 total landings, and between
27,080 and 37,625 total hours time-in-service.
The manufacturer evaluated trimmed sections of webs that contained
cracks. This evaluation revealed that the cracks, which were propagated
by fatigue, originated at the tangent point of the pocket fillet radius
on the forward surface, spread aft through the thickness of the web,
and then radiated vertically.
Because fuel on Model 747-200, -300, and -400 series airplanes is
located behind the front spar web, fuel could leak through these cracks
into the forward cargo bay. This leakage, if not corrected, could
result in a potential fire hazard.
Explanation of Relevant Service Information
The FAA has reviewed and approved Boeing Alert Service Bulletin
747-57A2298 Revision 1, dated September 12, 1996, which describes
procedures for conducting repetitive high frequency eddy current (HFEC)
inspections to detect cracking of the front spar web along the tangent
point of the pocket fillet radii. It also describes procedures for
repairing any cracking that is found during an inspection.
Additionally, the service bulletin describes procedures for an optional
HFEC inspection to confirm cracking, and repair if cracking is
confirmed.
Explanation of Requirements of Proposed AD
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 repetitive HFEC inspections to detect
cracking of the front spar web along the tangent point of the pocket
fillet radii., and repair, if necessary. These inspections and certain
repairs would be required to be performed in accordance with the alert
service bulletin described previously. Other repairs would be required
to be accomplished in accordance with a method approved by the FAA.
The proposed AD also would require that certain operators report
initial inspection results, positive or negative, to the FAA. Due to a
lack of information about the extent of cracking in the front spar web
of airplanes that have accumulated less than 18,000 total landings,
this information is needed to determine, among other things, how
widespread this occurrence might be among airplanes in this category,
the total number of accumulated landings when initial cracking may be
occurring, the size of cracking, and other conditions that may
contribute to cracking or its propagation.
Interim Action
This proposal is considered to be interim action until final action
is identified, at which time the FAA may consider further rulemaking.
Explanation of Applicability of Proposed AD
This proposed AD would be applicable only to Boeing Model 747-200,
-300, and -400 series airplanes.
Model 747-100, 747SR, and 747SP series airplanes are not included
in the applicability of this proposed AD because they have a dry bay
located behind the front spar web. This would preclude the type of
potential fire hazard situation addressed by this AD. In addition, if
the subject fatigue cracking were to occur on these airplanes, the
cabin pressure would vent through the front spar web and then the
limiting access holes of the front spar; this would result in a loss of
pressurization, but not sudden decompression.
Differences Between the Proposed AD and the Alert Service Bulletin
Operators should note that the alert service bulletin indicates
that vertical cracks of 10 inches or greater in length, or cracks that
extend in a diagonal direction (regardless of length), or cracks that
would affect an existing repair, should be repaired in accordance with
the manufacturer's instructions. However, the proposed AD would require
that these types of cracks be repaired in accordance with a method
approved by the FAA.
Cost Impact
There are approximately 485 Model 747-200, -300, and -400 series
airplanes of the affected design in the worldwide fleet. The FAA
estimates that 105 airplanes of U.S. registry would be affected by this
proposed AD, that it would take approximately 48 work hours per
airplane to accomplish the proposed actions, and that the average labor
rate is $60 per work hour. Based on these figures, the cost impact of
the proposed AD on U.S. operators is estimated to be $302,400, or
$2,880 per airplane, per inspection cycle.
The cost impact figure discussed above is 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 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.
[[Page 58671]]
Sec. 39.13 [Amended]
2. Section 39.13 is amended by adding the following new
airworthiness directive:
Boeing: Docket 96-NM-71-AD.
Applicability: Model 747-200, -300, and -400 series airplanes,
up to and including line number 744, certificated in any category.
Note 1: This AD applies to each airplane identified in the
preceding applicability provision, regardless of whether it has been
otherwise 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 (e) 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 the leakage of fuel into the forward cargo bay
through fatigue cracks in the front spar web, which could result in
a potential fire hazard, accomplish the following:
(a) Perform a high frequency eddy current (HFEC) inspection to
detect cracking of the front spar web of the center section of the
wing, in accordance with Boeing Alert Service Bulletin 747-57A2298,
Revision 1, dated September 12, 1996, at the time specified in
paragraph (a)(1) or (a)(2) of this AD, as applicable.
(1) For airplanes that have accumulated 12,000 to 17,999 total
landings as of the effective date of this AD: Within 12 months after
the effective date of this AD. Perform this inspection again prior
to the accumulation of 18,000 total landings or within 1,400
landings, whichever occurs later, and thereafter at intervals not to
exceed 1,400 landings.
(2) For all other airplanes: Prior to the accumulation of 18,000
total landings or within 12 months after the effective date of this
AD, whichever occurs later, and thereafter at intervals not to
exceed 1,400 landings.
(b) Except as provided by paragraph (c) of this AD, if any
cracking is detected during an inspection required by paragraph (a)
of this AD, prior to further flight, repair in accordance with
paragraph (b)(1) or (b)(2) of this AD, as applicable. Thereafter
repeat the HFEC inspection required by paragraph (a) of this AD at
intervals not to exceed 1,400 landings.
(1) If any vertical crack is found that is less than 10 inches
in length, repair in accordance with Boeing Alert Service Bulletin
747-57A2298, Revision 1, dated September 12, 1996.
(2) If any vertical crack is found that is 10 inches or greater
in length; or if any crack is found that has extended in a diagonal
direction (regardless of length); or if any crack is found that
would affect an existing repair; repair in accordance with a method
approved by the Manager, Seattle Aircraft Certification Office
(ACO), FAA, Transport Airplane Directorate.
(c) In lieu of accomplishing the procedures specified in
paragraph (b) of this AD: If a crack in the front spar web is
detected during an HFEC inspection required by paragraph (a) of this
AD, prior to further flight, operators may accomplish the procedures
for an optional HFEC inspection to confirm cracking, as described in
paragraph III.D.2. of the Accomplishment Instructions of Boeing
Alert Service Bulletin 747-57A2298, Revision 1, dated September 12,
1996.
(1) If this optional inspection is accomplished and cracking is
not confirmed, thereafter repeat the HFEC inspection specified in
paragraph (a) of this AD at intervals not to exceed 1,400 landings.
(2) If this optional inspection is accomplished and confirms
cracking, prior to further flight, repair the cracking in accordance
with paragraph (b)(1) or (b)(2) of this AD, as applicable.
(d) For airplanes that are required to perform an initial HFEC
inspection in accordance with paragraph (a)(1) of this AD: Within 30
days after accomplishing the initial inspection, submit a report of
inspection results, negative or positive, that includes the
information identified in paragraphs (d)(1) through (d)(5) of this
AD, to the Manager, Seattle Aircraft Certification Office, FAA,
Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton,
Washington 98055-4056; fax (206) 227-1181. 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.
(1) Airplane serial number.
(2) Total number of landings accumulated.
(3) Total number of hours time-in-service accumulated.
(4) Location, size and orientation of each crack.
(5) Whether fuel leakage resulted from the crack.
(e) 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 Directorate. 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.
(f) 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 November 8, 1996.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. 96-29417 Filed 11-15-96; 8:45 am]
BILLING CODE 4910-13-U
