[Federal Register Volume 59, Number 37 (Thursday, February 24, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-4128]


[[Page Unknown]]

[Federal Register: February 24, 1994]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 93-NM-139-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 inspections to detect fatigue-
related skin cracks and corrosion of the skin lap joints in the 
fuselage upper lobe, and repair, if necessary. This proposal would also 
require modification of certain lap joints and inspections of modified 
lap joints. This proposal is prompted by a structural review of Model 
747 series airplanes. The actions specified by the proposed AD are 
intended to prevent rapid decompression of the airplane and the 
inability to carry fail-safe loads.

DATES: Comments must be received by April 19, 1994.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-103, 
Attention: Rules Docket No. 93-NM-139-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 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-139-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-139-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    In April 1988, a transport category airplane managed to land after 
tiny cracks in rivet holes in the upper fuselage linked together, 
causing structural failure and explosive decompression. An 18-foot 
section ripped from the fuselage. This accident focused greater 
attention on the problem of aging aircraft.
    In June 1988, the FAA sponsored a conference on aging airplane 
issues, which was attended by representatives of the aviation industry 
from around the world. It became obvious that, because of the 
tremendous increase in air travel, the relatively slow pace of new 
airplane production, and the apparent economic feasibility of operating 
older technology airplanes rather than retiring them, increased 
attention needed to be focused on this aging fleet and maintaining its 
continued operational safety.
    The Air Transport Association (ATA) of America and the Aerospace 
Industries Association (AIA) of America committed to identifying and 
implementing procedures to ensure continuing structural airworthiness 
of aging transport category airplanes. An Airworthiness Assurance Task 
Force, with representatives from the aircraft operators, manufacturers, 
regulatory authorities, and other aviation representatives, was 
established in August 1988. The objective of the Task Force was to 
sponsor ``Working Groups'' to (1) select service bulletins, applicable 
to each airplane model in the transport fleet, to be recommended for 
mandatory modification of aging airplanes, (2) develop corrosion 
directed inspections and prevention programs, and (3) review the 
adequacy of each operator's structural maintenance program, (4) review 
and update the Supplemental Structural Inspection Documents (SSID), and 
(5) assess repair quality.
    The Working Group assigned to review the Boeing Model 747 series 
airplanes completed its work on Item (2) in July 1989 and developed a 
baseline program for controlling corrosion problems that may jeopardize 
the continued airworthiness of the Boeing Model 747 fleet. This program 
is contained in Boeing Document Number D6-36022, ``Aging Airplane 
Corrosion Prevention and Control Program--Model 747,'' dated July 1989. 
The FAA issued AD 90-25-05, Amendment 39-6790 (55 FR 49268, November 
27, 1990), which requires implementation of a corrosion prevention and 
control program.
    The Working Group completed a portion of its work on Item (1), 
above. The Working Group's proposal is contained in Boeing Document 
Number D6-35999, ``Aging Airplane Service Bulletin Structural 
Modification Program--Model 747.'' The FAA issued AD 90-06-06, 
Amendment 39-6490 (55 FR 8374, March 7, 1990), which requires the 
installation of the structural modifications identified in the 
document, and AD 92-27-04, Amendment 39-8437 (58 FR 8695, February 17, 
1993), which requires structural inspections of older airplanes.
    Additional structural inspections are required by AD 90-15-06, 
Amendment 39-6653 (55 FR 28600, July 12, 1990), which references Boeing 
Service Bulletin 747-53-2307, dated December 21, 1989. (A correction of 
the rule was published in the Federal Register on July 30, 1990 (55 FR 
31027).)
    The action being proposed herein follows from the ongoing 
activities of the Working Group relative to Item (1). The Working Group 
has identified certain service difficulties that warrant mandatory 
inspections following mandatory modification of these airplanes. The 
Working Group considers that these service difficulties can be 
controlled safely by repetitively inspecting following modification of 
these airplanes, and that, because of the safety implications, the 
inspections should be mandatory to assure that all operators perform 
them. Typically, the addressed unsafe conditions have occurred 
infrequently on older airplanes, and the Working Group has a very high 
degree of confidence in the ability of an inspection program to detect 
the damage before it impairs safety.
    The Working Group has reviewed Boeing Service Bulletin 747-53-2307, 
Revision 2, dated October 14, 1993, and has recommended it to the FAA 
for mandating of the described inspections to detect fatigue-related 
skin cracks and corrosion of the skin lap joints in the fuselage upper 
lobe, and necessary repair. The SWG also recommends modification of 
certain skin lap joints in the fuselage upper lobe that are fastened 
with deep countersink rivets on airplanes that have accumulated 20,000 
or more total landings. The upper skin panel in these particular lap 
joints has a doubler that is hot-bonded to the skin. The countersink 
depth of the rivet is greater than the basic skin gage. While this is 
not a problem for a skin panel with the hot bond intact, disbonding 
will result in a knife-edge condition in the skin layer. This condition 
causes these lap joints to be more susceptible to fatigue-related 
cracking. The SWG also recommends accomplishment of repetitive 
inspections of these modified lap joints. Accomplishment of these 
modifications and inspections will detect fatigue-related cracking and 
corrosion in a timely manner and will ensure the structural integrity 
of the skin lap joints beyond the design life of the airplane. The FAA 
has concurred with the Working Group's recommendations and has 
determined that AD action is warranted to mandate the inspections and 
modifications to assure the continued airworthiness of the Model 747 
fleet.
    The FAA has reviewed and approved Boeing Service Bulletin 747-53-
2307, Revision 2, dated October 14, 1993, that describes procedures for 
inspections to detect fatigue-related skin cracks and corrosion of the 
skin lap joints in the fuselage upper lobe, and repair, if necessary.
    The service bulletin also describes procedures for ``full'' 
modification of certain skin lap joints in the fuselage upper lobe that 
are fastened with deep countersink rivets on airplanes that have 
accumulated 20,000 total landings. Such rivets are used in the lap 
joints at the following locations:
    1. Stringer 12, left and right, from station 520 to 1,000; and
    2. Stringer 19, left and right, from station 520 to 740.
    The ``full'' modification for deep countersink rivets at these 
locations consists of opening the lap joint between circumferential 
splices, removing adhesive, repairing all cracks and corrosion, and 
reassembling the lap joint with \9/32\ inch protruding head rivets at 
all rivet locations.
    The service bulletin also describes procedures for repetitive 
external high frequency eddy current (HFEC) inspections to detect 
fatigue-related skin cracks of modified lap joints at the upper 
fastener row, and repair, if necessary.
    The service bulletin also describes procedures for an ``optional'' 
(partial) modification for certain lap joint areas that have an upper 
skin panel thickness of 0.090 inch or less and that do not have cracks 
or corrosion or an existing structural repair on the lap joint. The 
``optional'' (partial) modification consists of removing the upper row 
of rivets at a corrosion-free lap joint, performing an HFEC open hole 
inspection to detect cracks in removed rivet locations, and installing 
\1/4\-inch protruding head rivets.
    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 inspections to detect fatigue-related skin 
cracks and corrosion of the skin lap joints in the fuselage upper lobe, 
and repair, if necessary. The proposed AD would also require ``full'' 
modification of certain skin lap joints in the fuselage upper lobe that 
are fastened with deep countersink rivets on airplanes that have 
accumulated 20,000 total landings. The inspections and ``full 
modification'' would be required to be accomplished in accordance with 
the service bulletin described previously.
    The proposed AD would also require repetitive external HFEC 
inspections to detect fatigue-related skin cracks of modified lap 
joints, and repair, if necessary. After such repair, additional 
repetitive external HFEC inspections would be required. The HFEC 
inspections and repair would also be required to be accomplished in 
accordance with the service bulletin described previously.
    The proposed AD would also provide an ``optional'' (partial) 
modification for certain skin panels that have a thickness that is 
within specified limits, and that do not have cracks or corrosion or an 
existing structural repair on the lap joint. For those skin panels, 
this ``optional'' (partial) modification may be accomplished in lieu of 
the ``full'' modification. However, the ``optional'' (partial) 
modification may not be implemented at deep countersink fastener 
locations. The ``optional'' (partial) modification would be required to 
be accomplished in accordance with the service bulletin described 
previously.
    Accomplishment of the requirements of this proposed AD would 
terminate the requirements of AD 90-15-06, Amendment 39-6653 (55 FR 
28600, July 12, 1990). The FAA is considering further rulemaking action 
to revise AD 90-15-06, Amendment 39-6653, accordingly once this 
proposed AD becomes effective.
    There are approximately 200 Model 747 series airplanes of the 
affected design in the worldwide fleet. The FAA estimates that 116 
airplanes of U.S. registry would be affected by this proposed AD.
    The costs associated with the proposed inspections entail 100 work 
hours per airplane per inspection, at an average labor rate of $55 per 
work hour. (This figure does not include the time necessary for gaining 
access and closing up.) Based on these figures, the total cost impact 
of the proposed AD on U.S. operators, with regard to the proposed 
inspections, is estimated to be $638,000, or $5,500 per airplane per 
inspection.
    The costs associated with the proposed ``full'' modification entail 
approximately 96 work hours, for each 200-inch length of uncracked and 
uncorroded lap joint, at an average labor rate of $55 per work hour. 
(This figure does not include the time necessary for gaining access and 
closing up.) There are 100 lap joint sections per airplane, each with a 
length of 200 inches. The cost of required parts is expected to be 
negligible. Based on these figures, the total cost impact of the 
proposed AD on U.S. operators, with regard to the proposed ``full'' 
modification requirement, is estimated to be $61,248,000, or $528,000 
per airplane.
    The costs associated with the proposed initial HFEC inspection 
following modification entails approximately 56 work hours, at an 
average labor rate of $55 per work hour. Based on these figures, the 
total cost impact of the proposed AD on U.S. operators, with regard to 
the proposed initial HFEC inspection following modification, is 
estimated to be $357,280, or $3,080 per airplane.
    Based upon the figures discussed above, the total cost impact of 
the proposed AD on U.S. operators is expected to be $62,243,280, or 
$536,580 per airplane. This total cost figure includes the proposed 
inspections and modification, for the first year of the average five-
year inspection cycle. This total cost figure assumes that no operator 
has yet accomplished the proposed requirements of this proposed AD.
    The FAA recognizes that the proposed ``full'' modification would 
require a large number of work hours to accomplish. However, the 
proposed compliance time specified in paragraph (e) of this proposed AD 
should allow ample time for accomplishment of the ``full'' modification 
coincidentally with scheduled major airplane inspection and maintenance 
activities, thereby minimizing the costs associated with special 
airplane scheduling.
    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.
    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-139-AD.

    Applicability: Model 747 series airplanes, line positions 001 
through 200 inclusive, certificated in any category.
    Compliance: Required as indicated, unless accomplished 
previously.
    To prevent rapid decompression of the airplane and the inability 
to carry fail-safe loads, accomplish the following:
    (a) Within 1,000 landings after the effective date of this AD, 
and thereafter at the intervals specified in paragraphs (a)(1), 
(a)(2), and (a)(3) of this AD, perform inspections at the upper lobe 
skin lap joints in accordance with Boeing Service Bulletin 747-53-
2307, Revision 2, dated October 14, 1993:
    (1) Perform a detailed external visual inspection to detect 
cracks and evidence of corrosion (bulging skin between fasteners, 
blistered paint, dished fasteners, popped rivet heads, or loose 
fasteners) in accordance with the service bulletin. Repeat that 
inspection thereafter at intervals not to exceed 2,000 landings 
until the inspection required by paragraph (f) of this AD is 
accomplished.
    (2) Perform a high frequency eddy current inspection (HFEC) to 
detect cracks in the skin at the upper row of fasteners of the lap 
joints forward of body station (BS) 1000 in accordance with the 
service bulletin. Repeat that inspection thereafter at intervals not 
to exceed 4,000 landings until the modification required by 
paragraph (e) of this AD is accomplished.
    (3) Perform a HFEC inspection to detect cracks in the skin at 
the upper row of fastener holes of the lap joints aft of BS 1480 to 
2360 in accordance with the service bulletin. Repeat that inspection 
thereafter at intervals not to exceed 6,000 landings until the 
inspection required by paragraph (f) of this AD is accomplished.
    (b) If any crack is found during any inspection required by this 
AD, or if any corrosion is found for which material loss exceeds 10 
percent of the material thickness, accomplish paragraphs (b)(1) and 
(b)(2) of this AD in accordance with Boeing Service Bulletin 747-53-
2307, Revision 2, dated October 14, 1993.
    (1) Prior to further flight, repair any crack or corrosion 
found, in accordance with the service bulletin.
    (2) Within 15 months after accomplishing the repair, accomplish 
the ``full'' modification described in the service bulletin for the 
remainder of any skin panel lap joint in which a crack is found, or 
in which corrosion is found that exceeds 10 percent of the material 
thickness.
    (c) If no crack is found during any inspection required by this 
AD, but corrosion is found for which the material loss does not 
exceed 10 percent of the material thickness: Accomplish paragraph 
(c)(1) and (c)(2) of this AD for the entire affected skin panel lap 
joint in accordance with Boeing Service Bulletin 747-53-2307, 
Revision 2, dated October 14, 1993.
    (1) Within 500 landings after accomplishing the inspection 
during which the corrosion was found, and thereafter at intervals 
not to exceed 500 landings until the ``full'' modification required 
by paragraph (c)(2) of this AD is accomplished: Perform a HFEC 
inspection to detect cracks of the corroded lap joint, in accordance 
with the service bulletin.
    (2) Within 30 months after accomplishing the inspection during 
which the corrosion was found: Accomplish the ``full'' modification 
required by paragraph (e) of this AD.
    (d) The inspections required by this AD shall be performed by 
removing the paint and using an approved chemical stripper; or by 
ensuring that each fastener head is clearly visible.
    (e) Except as provided in paragraph (g) of this AD, prior to the 
accumulation of 20,000 total landings, or within the next 1,000 
landings after the effective date of this AD, whichever occurs 
later: Accomplish the modification described in the service bulletin 
as a ``full'' modification of the skin lap joints at the locations 
specified in paragraphs (e)(1) and (e)(2) of this AD, as applicable, 
in accordance with Boeing Service Bulletin 747-53-2307, Revision 2, 
dated October 14, 1993.
    (1) For airplane line numbers 001 through 058, inclusive: Modify 
the skin lap joints at Stringer 12 (left and right), station 520 to 
1,000; and Stringer 19 (left and right), station 520 to 740.
    (2) For airplane line numbers 59 through 200, inclusive: Modify 
the skin lap joints at Stringer 12 (left and right), station 740 to 
1,000; and Stringer 19 (left and right), station 520 to 740.
    (f) Perform an external HFEC inspection to detect skin cracks of 
any modified skin lap joints at the times specified in paragraphs 
(f)(1), (f)(2), and (f)(3) of this AD, as applicable, in accordance 
with Boeing Service Bulletin 747-53-2307, Revision 2, dated October 
14, 1993. Repeat that inspection thereafter at intervals not to 
exceed 3,000 landings. Accomplishment of this inspection terminates 
the repetitive inspection requirements of paragraph (a) of this AD.
    (1) For airplanes on which the ``full'' modification has been 
accomplished: Within 10,000 landings after accomplishment of that 
modification.
    (2) For airplanes on which the ``optional'' (partial) 
modification has been accomplished: Within 7,000 landings after 
accomplishment of that modification.
    (3) For airplanes having deep countersink fasteners located at 
Section 42 on which the ``full'' modification, as described in the 
original issue of the service bulletin, has been accomplished: 
Within 5,000 landings after accomplishment of that modification.
    (g) In lieu of the ``full'' modification required by paragraph 
(e) of this AD, the ``optional'' (partial) modification described in 
Boeing Service Bulletin 747-53-2307, Revision 2, dated October 14, 
1993, may be accomplished for skin panels that have an outer 
thickness of 0.090 inches or less, and that do not have any cracks, 
corrosion, or an existing structural repair on the lap joint. The 
``optional'' (partial) modification shall not be accomplished at 
deep countersink fastener locations.
    (h) Accomplishment of the requirements of this AD terminates the 
requirements of AD 90-15-06, Amendment 39-6653.
    (i) 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.

    (j) Special flight permits may be issued in accordance with 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 17, 1994.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 94-4128 Filed 2-23-94; 8:45 am]
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