[Federal Register Volume 62, Number 38 (Wednesday, February 26, 1997)]
[Rules and Regulations]
[Pages 8613-8615]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 97-4555]



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  Federal Register / Vol. 62, No. 38 / Wednesday, February 26, 1997 / 
Rules and Regulations  

[[Page 8613]]



DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 96-NM-71-AD; Amendment 39-9945; AD 97-05-01]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 747-200, -300, and -400 
Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

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SUMMARY: This amendment adopts a new airworthiness directive (AD), 
applicable to certain Boeing Model 747-200, -300, and -400 series 
airplanes, that requires repetitive inspections to detect cracking of 
the front spar web of the center section of the wing, and repair, if 
necessary. This amendment is prompted by reports of fatigue cracking 
found in the front spar web. The actions specified by this 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: Effective April 2, 1997.
    The incorporation by reference of certain publications listed in 
the regulations is approved by the Director of the Federal Register as 
of April 2, 1997.

ADDRESSES: The service information referenced in this AD may be 
obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, 
Washington 98124-2207. This information may be examined at the Federal 
Aviation Administration (FAA), Transport Airplane Directorate, Rules 
Docket, 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: 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: A proposal to amend part 39 of the Federal 
Aviation Regulations (14 CFR part 39) to include an airworthiness 
directive (AD) that is applicable to certain Boeing Model 747-200, -
300, and -400 series airplanes was published in the Federal Register on 
November 18, 1996 (61 FR 58669). That action proposed to 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.
    Interested persons have been afforded an opportunity to participate 
in the making of this amendment. Due consideration has been given to 
the comments received.

Support for the Proposal

    Three commenters support the proposed AD.

Request to Extend Initial Compliance Time

    One commenter requests that the proposal be revised to extend the 
compliance time for the initial inspection from the proposed 12 months 
to 18 months. The commenter requests this extension so that affected 
operators will be able to perform the inspection during a regularly 
scheduled maintenance visit. The extent of the work involved in the 
proposed inspection, and any necessary repair, cannot be accomplished 
at a line station, but must be accomplished when the airplane would be 
located at a main base where special equipment and trained personnel 
would be readily available. The commenter states that the adoption of 
the proposed compliance time of 12 months would require operators to 
schedule special times for the accomplishment of the inspection, at 
additional expense and downtime.
    Further, this commenter states that the wing center section front 
spar web is inspected currently on some affected airplanes under the 
Supplemental Structural Inspection Document (SSID) program, which was 
mandated most recently by AD 94-15-18, amendment 39-8989 (59 FR 41233, 
August 11, 1994). There have been no reports of cracks found in this 
front spar web area during these required inspections. Additionally, 
the commenter states that, since June 1995, at least 3 airplanes in its 
fleet have undergone either NDT or visual inspections, and no cracks or 
other problems were found on the subject front spar web. The commenter 
requests that the FAA take this experience into consideration and 
extend the proposed compliance threshold as requested.
    The FAA does not concur. Leakage of fuel into the forward cargo 
bay, as a result of fatigue cracking in the front spar web, is a 
significant safety issue, and the FAA has determined that the 
inspection threshold, as proposed, is warranted. The FAA considered not 
only these safety issues in developing an appropriate compliance time 
for this action, but the recommendations of the manufacturer, the 
availability of any necessary repair parts, and the practical aspect of 
accomplishing the required inspection within an interval of time that 
parallels normal scheduled maintenance for the majority of affected 
operators.
    The FAA points out that the manufacturer recommended that the 
inspections begin within 18 months after the release of Boeing Service 
Bulletin 747-57A2298, Revision 1, on September 12, 1996; that interval 
corresponds to most operators' scheduled ``C'' checks. The FAA took 
this recommendation into account, as well as the time that would be 
necessary to complete the rulemaking process, and found that a 12-month 
initial compliance time should fall well within the time that the 
majority of operators have regular maintenance visits scheduled.
    As for the results of inspections previously performed on the 
affected area, the FAA points out that this AD action was based on 
reports from two operators who did find cracking in the wing center 
section front spar web on at least three airplanes; the longest crack 
found was 17 inches. While those cracks were found on Model 747-100 
series airplanes, the FAA maintains that similar cracking is likely to 
develop on Model 747-200, -300, and -400 series airplanes up to line 
number 744 because those models have the same web thickness and similar 
loading as the Model 747-100.

[[Page 8614]]

    In light of these factors, the FAA has determined that the 12-month 
initial compliance time, as proposed, is appropriate. The FAA points 
out that, if operators already have accomplished the initial inspection 
within the last 12 months prior to the effective date of the AD, they 
are given ``credit'' for that inspection as compliance with the initial 
inspection requirement of the AD. The final rule has been revised to 
clarify this point.

Request To Extend Repetitive Inspection Intervals

    One commenter requests that the proposal be revised to extend the 
repetitive inspection interval from the proposed 1,400 cycles to 2,000 
cycles. The commenter, a U.S. operator, states that it already has 
inspected several of the airplanes in its fleet and has found no 
cracking. In addition, the commenter points out that the inspection 
area will be visually inspected at regular intervals to detect 
corrosion as part of the Boeing 747 Corrosion Prevention and Control 
Program, which was mandated by AD 90-25-05, amendment 39-6790 (55 FR 
49268, November 27, 1990).
    The FAA does not concur, since the commenter provided no technical 
justification for an extension. The repetitive interval of 1,400 cycles 
is based on damage tolerance and crack growth analyses that the 
manufacturer performed. Additionally, the interval was calculated based 
on accomplishing high frequency eddy current (HFEC) inspections, and 
the effectiveness of those inspections in detecting cracking. The FAA 
acknowledges that visual inspections to detect corrosion of the area 
are mandated by AD 90-25-05; however, the HFEC inspections required by 
this AD will provide a much higher level of precision than visual 
inspections, and will be able to detect cracking far earlier than could 
be discovered by visual inspections alone.

Request To Revise Method of Counting Accumulated Cycles

    One commenter requests that the proposal be revised to include a 
provision specifying that pressurization cycles of 2.0 psi or less need 
not be counted as a flight cycle when determining the number of flight 
cycles relative to the proposed compliance thresholds. The commenter 
states that cabin pressure is the main contributor to stresses in the 
center section front spar web, but a cabin pressure of 2.0 psi would 
result in stresses of less than one-fourth the normal operating level. 
Further, with a maximum cabin pressure at 2.0 psi, the fatigue damage 
per cycle would be reduced by a factor of approximately 100.
    The FAA does not concur with the commenter's request. The FAA 
considers that flights with less than 2.0 psi cabin pressure may 
contribute a negligible amount of fatigue damage to the front spar web 
of the wing center section. However, a pressurization cycle of 2.0 psi 
or less is a typical pressure used during flight training, and is not 
typical of normal operation of the affected airplanes. The FAA does not 
consider it appropriate to include various provisions in an AD 
applicable to a unique use of an affected airplane. Paragraph (e) of 
this final rule provides for the approval of alternative methods of 
compliance to address these types of unique circumstances.

Conclusion

    After careful review of the available data, including the comments 
noted above, the FAA has determined that air safety and the public 
interest require the adoption of the rule with the one change described 
previously. The FAA has determined that this change will neither 
increase the economic burden on any operator nor increase the scope of 
the AD.

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 will be affected by this 
AD, that it will take approximately 48 work hours per airplane to 
accomplish the required inspections, and that the average labor rate is 
$60 per work hour. Based on these figures, the cost impact of the AD on 
U.S. operators is estimated to be $302,400, or $2,880 per airplane, per 
inspection.
    The cost impact figure discussed above is based on assumptions that 
no operator has yet accomplished any of the 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 adopted herein will 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 final 
rule does not have sufficient federalism implications to warrant the 
preparation of a Federalism Assessment.
    For the reasons discussed above, I certify that this action (1) is 
not a ``significant regulatory action'' under Executive Order 12866; 
(2) is not a ``significant rule'' under DOT Regulatory Policies and 
Procedures (44 FR 11034, February 26, 1979); and (3) 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 final evaluation has been prepared for this action 
and it is contained in the Rules Docket. A copy of it may be obtained 
from the Rules Docket at the location provided under the caption 
ADDRESSES.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Incorporation by 
reference, Safety.

Adoption of the Amendment

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation Administration amends 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:

97-05-01  Boeing: Amendment 39-9945. 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:

[[Page 8615]]

    (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: Perform the initial 
inspection within 12 months after the effective date of this AD, 
unless previously accomplished within the last 12 months. Perform 
this inspection again prior to the accumulation of 18,000 total 
landings or within 1,400 landings, whichever occurs later; after 
accomplishing the initial inspection, and thereafter at intervals 
not to exceed 1,400 landings.
    (2) For all other airplanes: Perform the initial inspection 
prior to the accumulation of 18,000 total landings or within 12 
months after the effective date of this AD, whichever occurs later. 
Repeat this inspection 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.
    (g) The actions shall be done in accordance with Boeing Alert 
Service Bulletin 747-57A2298, Revision 1, dated September 12, 1996. 
This incorporation by reference was approved by the Director of the 
Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 
51. Copies may be obtained from Boeing Commercial Airplane Group, 
P.O. Box 3707, Seattle, Washington 98124-2207. Copies may be 
inspected 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.
    (h) This amendment becomes effective on April 2, 1997.

    Issued in Renton, Washington, on February 19, 1997.
James V. Devany,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 97-4555 Filed 2-25-97; 8:45 am]
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