[Federal Register Volume 59, Number 43 (Friday, March 4, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-4954]
[[Page Unknown]]
[Federal Register: March 4, 1994]
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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39
[Docket No. 93-NM-212-AD]
Airworthiness Directives; Boeing Model 747 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 series
airplanes. This proposal would require inspection to detect cracking of
certain fuselage longitudinal lap joints, repair of any cracking found,
and replacement of the countersunk fasteners in those laps joints with
protruding head fasteners. This proposal is prompted by a structural
reassessment of Model 747 series airplanes. The actions specified by
the proposed AD are intended to prevent skin cracking in the
longitudinal lap joints of certain stringers, which can lead to rapid
decompression of the airplane.
DATES: Comments must be received by April 29, 1994.
ADDRESSES: Submit comments in triplicate to the Federal Aviation
Administration (FAA), Transport Airplane Directorate, ANM-103,
Attention: Rules Docket No. 93-NM-212-AD, 1601 Lind Avenue, SW.,
Renton, Washington 98055-4056. Comments may be inspected at this
location between 9 a.m. and 3 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: Steven C. Fox, Aerospace Engineer,
Airframe Branch, ANM-120S, FAA, Transport Airplane Directorate, Seattle
Aircraft Certification Office, 1601 Lind Avenue, SW., Renton,
Washington 98055-4056; telephone (206) 227-2777; 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 93-NM-212-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-103, Attention: Rules
Docket No. 93-NM-212-AD, 1601 Lind Avenue, SW., Renton, Washington
98055-4056.
Discussion
Recently, the Boeing Commercial Airplane Group, manufacturer of
Model 747 series airplanes, conducted a structural reassessment of
these airplanes. The FAA has reviewed the results of this reassessment
and has determined that the longitudinal lap joints of Stringer (S-)12
are critical to the structural integrity of these airplanes. -
The upper skin in the S-12 longitudinal lap joints are made of
waffle doublers that are hot bonded to skin panels. The S-12
longitudinal lap joints have three rows of countersunk fasteners. The
depth of the countersink exceeds the thickness of the skin panel. If
the waffle doubler disbonds from the skin panel, the resultant sharp
edges at the longitudinal lap joint fasteners can cause fatigue
cracking at the fastener holes.
Skin cracking in the longitudinal lap joints of S-12L and S-12R, if
not detected and corrected, could result in rapid decompression of the
airplane.
The FAA has reviewed and approved Boeing Service Bulletin 747-53-
2366, dated August 6, 1992, that describes procedures for repetitive
high frequency eddy current (HFEC) inspections to detect cracking of
the skin around the fasteners in the upper row of the longitudinal lap
joints of S-12L and S-12R from station 520 to station 741.1, and
replacement of the countersunk fasteners in these longitudinal lap
joints with protruding head fasteners.
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 external HFEC inspections to
detect cracking of the skin around the fasteners in the upper row of
the longitudinal lap joints of S-12L and S-12R from station 520 to
station 741.1, and replacement of the countersunk fasteners in these
longitudinal lap joints with protruding head fasteners. The actions
would be required to be accomplished in accordance with the service
bulletin described previously. This proposal also would require repair
of all cracking in accordance with procedures specified in the 747
Structural Repair Manual.
This proposal is applicable only to airplanes having line numbers
201 through 230. Since the tolerance specifications for the bonding
process for airplanes manufactered after line number 230 were more
stringent, those airplanes are not subject to the unsafe condition
addressed by this proposed AD.
There are approximately 30 Model 747 series airplanes of the
affected design in the worldwide fleet. The FAA estimates that 12
airplanes of U.S. registry would be affected by this proposed AD, that
it would take approximately 17 work hours per airplane to accomplish
the proposed inspections, and that the average labor rate is $55 per
work hour. Based on these figures, the total cost impact of the
proposed inspections on U.S. operators is estimated to be $11,220, or
$935 per airplane.
The FAA estimates that it would take approximately 302 work hours
per airplane to accomplish the proposed requirement to replace
fasteners, and that the average labor rate is $55 per work hour.
Required parts would be nominal in cost. Based on these figures, the
total cost impact of the proposed requirement to replace fasteners on
U.S. operators is estimated to be $199,320, or $16,610 per airplane.
Based on the figures, above, the total cost impact of the proposed
actions (cost of inspections added to the cost of replacement of
fasteners) on U.S. operators is estimated to be $210,540, or $17,545
per airplane.
The FAA recognizes that the proposed replacement of fasteners would
require a large number of work hours to accomplish. However, the 4-year
compliance time specified in paragraph (b) of this proposed AD should
allow ample time for the replacement of the fasteners to be
accomplished coincidentally with scheduled major airplane inspection
and maintenance activities, thereby minimizing the costs associated
with special airplane scheduling. -
The total 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.
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 14
CFR part 39 of the Federal Aviation Regulations as follows:
PART 39--AIRWORTHINESS DIRECTIVES -
1. The authority citation for part 39 continues to read as follows:
Authority: 49 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C.
106(g); and 14 CFR 11.89.
Sec. 39.13 [Amended] -
2. Section 39.13 is amended by adding the following new
airworthiness directive:
Boeing: Docket 93-NM-212-AD.
Applicability: Model 747 series airplanes, having line numbers
201 through 230 inclusive; certificated in any category. -
Compliance: Required as indicated, unless accomplished
previously.
To prevent rapid decompression of the airplane, accomplish the
following:
(a) Prior to the accumulation of 15,000 total flight cycles or
within 1,000 flight cycles after the effective date of this AD,
whichever occurs later, perform an external high frequency eddy
current (HFEC) inspection to detect cracking of the skin at the
upper row of countersunk fasteners in the longitudinal lap joints of
Stringer (S-)12L and S-12R from station 520 to station 741.1, in
accordance with Boeing Service Bulletin 747-53-2366, dated August 6,
1992.
(1) If no cracking is found, repeat the inspection thereafter at
intervals not to exceed 4,000 flight cycles until the replacement of
fasteners required by paragraph (b) of this AD is accomplished.
(2) If any cracking is found, prior to further flight, repair in
accordance with the 747 Structural Repair Manual. After repair,
repeat the inspection at intervals not to exceed 4,000 flight cycles
until the replacement of fasteners required by paragraph (b) of this
AD is accomplished.
(b) Prior to the accumulation of 20,000 total flight cycles or
within 4 years after the effective date of this AD, whichever occurs
later, replace the countersunk fasteners in the upper row of the
longitudinal lap joints of S-12L and S-12R from station 520 to
station 741.1 with protruding head fasteners in accordance with
Boeing Service Bulletin 747-53-2366, dated August 6, 1992.
Replacement of these fasteners constitutes terminating action for
the repetitive inspections required by paragraph (a) of this AD.
(c) Prior to the accumulation of 10,000 total flight cycles
after replacement of the countersunk fasteners required by paragraph
(b) of this AD, perform an external HFEC inspection to detect
cracking of the skin at the upper row of protruding head fasteners
in the longitudinal lap joints of S-12L and S-12R from station 520
to station 741.1 in accordance with Boeing Service Bulletin 747-53-
2366, dated August 6, 1992.
(1) If no cracking is found, repeat the inspection thereafter at
intervals not to exceed 3,000 flight cycles.
(2) If any cracking is found, prior to further flight, repair in
accordance with the 747 Structural Repair Manual. After repair,
repeat the inspection at intervals not to exceed 3,000 flight
cycles.
(d) 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: Information concerning the existence of approved
alternative methods of compliance with this AD, if any, may be
obtained from the Seattle ACO.
(e) Special flight permits may be issued in accordance with
Federal Aviation Regulations (FAR) 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 February 28, 1994.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. 94-4954 Filed 3-3-94; 8:45 am]
BILLING CODE 4910-13-U
