[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]
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