[Federal Register Volume 63, Number 149 (Tuesday, August 4, 1998)]
[Proposed Rules]
[Pages 41483-41485]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-20675]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 97-NM-87-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 747-100, -200, and -300 
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 747-100, -
200, and -300 series airplanes. This proposal would require repetitive 
inspections to detect cracking of certain lower lobe fuselage frames, 
and repair, if necessary. This proposal 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 the proposed 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: Comments must be received by September 18, 1998.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 97-NM-87-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: 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:

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 97-NM-87-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. 97-NM-87-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    The FAA has received reports indicating that fatigue cracking was 
found on a total of 19 lower lobe fuselage frames on Boeing Model 747 
series airplanes. Two of these airplanes had completely severed frame 
inner chords, webs, and fail-safe chords on adjacent frames. A severed 
frame will result in increased fuselage skin stresses, which could lead 
to skin cracking. In the area of the lower lobe fuselage frames from 
Body Station (BS) 1820 to BS 2100, the fuselage skin does not have 
tearstraps to arrest a skin crack. Instead of tearstraps, this area has 
fail-safe chords attached to the fuselage frames which reduce the 
stress levels in the fuselage skin such that a crack in the skin would 
be stopped. With a completely severed fuselage frame inner chord, web, 
and fail-safe chord, there is nothing to prevent a skin crack from 
propagating beyond several fuselage frame bays. This condition, if not 
detected and corrected, could result in rapid decompression of the 
airplane.

Explanation of Relevant Service Information

    The FAA has reviewed and approved Boeing Alert Service Bulletin 
747-53A2408, dated April 25, 1996, which describes procedures for 
repetitive detailed visual inspections to detect cracking of the lower 
lobe fuselage frames from BS 1820 to BS 2100, and repair, if necessary.

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 the Proposed AD and Relevant Service Bulletin

    Operators should note that, unlike the initial compliance time 
(specified as prior to the accumulation of 16,000 total flight cycles, 
or within 1,500 flight cycles or 18 months, whichever occurs first) for 
airplanes identified in the alert service bulletin, the proposed AD 
would require that those airplanes be inspected prior to the 
accumulation of 15,000 total flight cycles, or within 1,500 flight 
cycles or 18 months, whichever occurs first. Because the FAA received a 
report of cracking on an airplane that had accumulated only 15,227 
total flight cycles, the FAA finds a compliance threshold of 15,000 
total flight cycles for initiating the proposed actions to be 
warranted, in that it represents an appropriate interval of time 
allowable for affected airplanes to continue to operate without 
compromising safety.
    Operators also should note that, although the alert service 
bulletin 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), the proposed AD does not. The FAA received a report 
of cracking on an airplane that had accumulated 12,817 full pressure 
cycles, plus 8,761 cycles at less than 2.0 psi differential pressure. 
The reported cracking was more

[[Page 41484]]

indicative of an airplane that had accumulated 20,000 total flight 
cycles. If this proposed AD were to allow discount of flight cycles, as 
recommended in the alert service bulletin, the actions required by this 
proposed AD would not be required to be accomplished on the airplane 
discussed previously. Therefore, cracking on that airplane would have 
gone undetected. These facts indicate that discounting cycles at or 
below a cabin pressure differential of 2.0 psi is not warranted for the 
proposed AD.
    The alert service bulletin also allows operators of Model 747SR 
series airplanes to use a 1.2 adjustment factor for the reduction of 
the inspection compliance threshold and interval. In previous AD's, the 
FAA has allowed the use of the 1.2 adjustment factor for these 
airplanes; however, data have since become available to the FAA that 
indicate the use of the 1.2 adjustment factor is unconservative. The 
FAA has determined that use of the 1.2 adjustment factor is not in the 
best interest of aviation safety, and that its use shall be 
discontinued. Therefore, the proposed AD does not allow reduction of 
the inspection compliance threshold and interval for operators of Model 
747SR series airplanes that operate at reduced cabin differential 
pressure.
    The alert service bulletin specifies that, in the event that 
cracking is found during the inspection of the lower lobe frames, an 
inspection of the fuselage skin should be conducted in accordance with 
the 747 Structural Repair Manual (SRM) or inspection data supplied by 
the manufacturer. However, the proposed AD requires a detailed visual 
inspection of the adjacent structure within 20 inches of the crack 
location on the frame to detect fuselage skin cracking.
    In addition, although the alert service bulletin specifies that 
certain repairs required by this proposed AD may be accomplished in 
accordance with the 747 SRM or repair data supplied by the 
manufacturer, the proposed AD would require that those repairs be 
accomplished in accordance with the 747 SRM or in accordance with a 
method approved by the FAA.

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 
proposed AD.

Cost Impact

    There are approximately 452 airplanes of the affected design in the 
worldwide fleet. The FAA estimates that 152 airplanes of U.S. registry 
would be affected by this proposed AD, that it would take approximately 
2 work hours per airplane to accomplish the proposed inspection, and 
that the average labor rate is $60 per work hour. Based on these 
figures, the cost impact of the inspection proposed 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 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.


Sec. 39.13  [Amended]

    2. Section 39.13 is amended by adding the following new 
airworthiness directive:

Boeing: 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

[[Page 41485]]

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.

    (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.
    (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, or in accordance with the Boeing 747 Structural Repair 
Manual.
    (2) Repeat the inspection required by paragraph (a) of this AD 
thereafter at intervals not to exceed 3,000 flight cycles.
    (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.
    (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. 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.

    (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 July 27, 1998.
S.R. Miller,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 98-20675 Filed 8-3-98; 8:45 am]
BILLING CODE 4910-13-P