[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