[Federal Register Volume 64, Number 61 (Wednesday, March 31, 1999)]
[Rules and Regulations]
[Pages 15298-15300]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-7554]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 97-NM-87-AD; Amendment 39-11097; AD 99-07-12]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 747-100, -200, and -300 
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 747-100, -200, and -300 series 
airplanes, that requires repetitive inspections to detect cracking of 
certain lower lobe fuselage frames, and repair, if necessary. This 
amendment is prompted by reports indicating that fatigue cracks were 
found in lower lobe frames on the left side of the fuselage. The 
actions specified by this AD are intended to detect and correct fatigue 
cracking of certain lower lobe fuselage frames, which could lead to 
fatigue cracks in the fuselage skin, and consequent rapid decompression 
of the airplane.

DATES: Effective May 5, 1999.
    The incorporation by reference of certain publications listed in 
the regulations is approved by the Director

[[Page 15299]]

of the Federal Register as of May 5, 1999.

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: Bob Breneman, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA, Transport Airplane Directorate, Seattle 
Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056; telephone (425) 227-2776; fax (425) 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 747-100, -
200, and -300 series airplanes was published in the Federal Register on 
August 4, 1998 (63 FR 41483). That action proposed to require 
repetitive inspections to detect cracking of certain lower lobe 
fuselage frames, and repair, if necessary.

Comments Received

    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 Proposed Rule

    Two commenters support the proposed rule.

Request To Increase the Threshold and Allow Discounting of Flights 
Below 2.0 PSI

    One commenter requests that the proposed AD be revised to reflect 
the threshold of 16,000 flight cycles, as recommended in Boeing Alert 
Service Bulletin 747-53A2408, dated April 25, 1996 (which is referenced 
in the proposed AD as the appropriate source of service information for 
accomplishment of the required actions), and to allow discounting of 
flight cycles less than 2.0 pounds per square inch (psi). The commenter 
states that the critical crack is not a severed frame, but a severed 
frame with a skin crack. The commenter further states that there were 
no reports of skin cracking associated with the cracked frames, and 
that analysis shows that an existing skin crack at a severed frame will 
not grow to critical length prior to the inspection threshold 
identified in the referenced service bulletin. In addition, the fleet 
reports used in this analysis were adjusted to account for flights less 
that 2.0 psi.
    The FAA does not concur with the commenter's request. As discussed 
under the heading ``Differences Between the Proposed AD and Relevant 
Service Bulletin'' in the preamble of the proposed AD, the FAA has 
received a report of cracking (i.e., a completely severed frame, 
consisting of the frame web, inner chord, and fail-safe chord) on an 
airplane that had accumulated only 15,227 total flight cycles. As a 
result, the FAA determined that a compliance threshold of 15,000 total 
flight cycles for initiating the required actions is warranted, in that 
it represents an appropriate interval of time allowable for affected 
airplanes to continue to operate without compromising safety.
    In the same regard, the FAA does not find that allowing the 
discount of flight cycles below 2.0 psi would adequately address the 
unsafe condition. The FAA has received a report of two adjacent frames 
being completely severed on an airplane that had accumulated 12,817 
full pressure cycles, plus 8,761 cycles at less than 2.0 psi 
differential pressure. As stated in the NPRM, this reported cracking is 
more indicative of the reported findings on airplanes that had 
accumulated 20,000 total flight cycles. If the FAA allowed the discount 
of flight cycles below 2.0 psi, as recommended in the referenced 
service bulletin, the identified unsafe condition on that airplane 
would go undetected for several thousand flight cycles. Therefore, the 
FAA finds that no change to the final rule is necessary.

Explanation of Changes Made to the Proposal

    The FAA has revised paragraph (c)(1) of the final rule to also 
allow repair of any crack in the subject area to be accomplished in 
accordance with data meeting the type certification basis of the 
airplane approved by a Boeing Company Designated Engineering 
Representative who has been authorized by the FAA to make such 
findings.

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 change previously 
described. The FAA has determined that the change will neither increase 
the economic burden on any operator nor increase the scope of the AD.

Interim Action

    This is considered to be interim action until the accomplishment of 
AD 93-08-12, amendment 39-8559 (58 FR 27927, May 12, 1993). That AD 
requires a detailed visual internal inspection to detect cracks in the 
Section 46 lower lobe frames, and repair, if necessary, in accordance 
with Boeing Service Bulletin 747-53-2349, dated June 27, 1991. The 
initial inspection required by AD 93-08-12 is required prior to the 
accumulation of 22,000 total flight cycles. The FAA now finds that 
earlier inspection (i.e., prior to accumulation of 15,000 total flight 
cycles) of the lower lobe frames is warranted, as required by this AD.

Cost Impact

    There are approximately 452 Model Boeing 747-100, -200, and -300 
series airplanes of the affected design in the worldwide fleet. The FAA 
estimates that 152 airplanes of U.S. registry will be affected by this 
AD, that it will take approximately 2 work hours per airplane to 
accomplish the required inspection, and that the average labor rate is 
$60 per work hour. Based on these figures, the cost impact of the 
inspection required by this AD on U.S. operators is estimated to be 
$18,240, or $120 per airplane, per inspection cycle.
    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

[[Page 15300]]

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:

99-07-12  Boeing: Amendment 39-11097. Docket 97-NM-87-AD.

    Applicability: Model 747-100, -200, and -300 series airplanes, 
as listed in Boeing Alert Service Bulletin 747-53A2408, dated April 
25, 1996; 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 (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 detect and correct fatigue cracking of certain lower lobe 
fuselage frames, which could lead to fatigue cracks in the fuselage 
skin, and consequent rapid decompression of the airplane, accomplish 
the following:

    Note 2: Although Boeing Alert Service Bulletin 747-53A2408, 
dated April 25, 1996, allows discount from the compliance threshold 
of all flight cycles at or below a cabin pressure differential of 
2.0 pounds per square inch (psi), this AD requires that all flight 
cycles be counted.

    (a) For airplanes on which the initial detailed visual internal 
inspection of the Section 46 lower lobe frames required by paragraph 
(a)(3) of AD 93-08-12, amendment 39-8559, has not been accomplished: 
Perform a detailed visual inspection to detect cracking of the lower 
lobe fuselage frames from Body Station 1820 to Body Station 2100, in 
accordance with Boeing Alert Service Bulletin 747-53A2408, dated 
April 25, 1996, at the later of the times specified in paragraphs 
(a)(1) and (a)(2) of this AD:
    (1) Prior to the accumulation of 15,000 total flight cycles; or
    (2) Within 1,500 flight cycles or 18 months after the effective 
date of this AD, whichever occurs first.

    Note 3: Paragraph (a)(3) of AD 93-08-12 requires a detailed 
visual internal inspection to detect cracks in the Section 46 lower 
lobe frames, in accordance with Boeing Service Bulletin 747-53-2349, 
dated June 27, 1991. The initial inspection is required prior to the 
accumulation of 22,000 total flight cycles, or within 1,000 flight 
cycles after June 11, 1993 (the effective date of AD 93-08-12), 
whichever occurs later.

Repetitive Inspections

    (b) If no cracking is detected during the inspection required by 
paragraph (a) of this AD, repeat the inspection thereafter at 
intervals not to exceed 3,000 flight cycles.

Corrective Actions

    (c) If any cracking is detected during any inspection required 
by paragraph (a) of this AD, prior to further flight, accomplish 
paragraphs (c)(1) and (c)(2) of this AD:
    (1) Within 20 inches of the crack location on the frame, perform 
a detailed visual inspection of the adjacent structure to detect 
cracking. If any cracking is detected, prior to further flight, 
repair in accordance with a method approved by the Manager, Seattle 
Aircraft Certification Office (ACO), FAA, Transport Airplane 
Directorate; the Boeing 747 Structural Repair Manual; or in 
accordance with data meeting the type certification basis of the 
airplane approved by a Boeing Company Designated Engineering 
Representative who has been authorized by the Manager, Seattle ACO, 
to make such findings.
    (2) Repeat the inspection required by paragraph (a) of this AD 
thereafter at intervals not to exceed 3,000 flight cycles.

Optional Terminating Inspection

    (d) Accomplishment of the initial detailed visual internal 
inspection of the Section 46 lower lobe frames required by paragraph 
(a)(3) of AD 93-08-12 constitutes terminating action for the 
requirements of this AD.

Alternative Methods of Compliance

    (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 Aircraft Certification 
Office (ACO), FAA, Transport Airplane 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 4: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

Special Flight Permits

    (f) Special flight permits may be issued in accordance with 
Secs. 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.

Incorporation by Reference

    (g) Except as provided by paragraphs (c)(1) and (d) of this AD, 
the actions shall be done in accordance with Boeing Alert Service 
Bulletin 747-53A2408, dated April 25, 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 May 5, 1999.

    Issued in Renton, Washington, on March 22, 1999.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 99-7554 Filed 3-30-99; 8:45 am]
BILLING CODE 4910-13-P