[Federal Register Volume 59, Number 112 (Monday, June 13, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-13852]


[[Page Unknown]]

[Federal Register: June 13, 1994]


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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 93-NM-139-AD; Amendment 39-8937; AD 94-12-09]

 

Airworthiness Directives; Boeing Model 747 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 series airplanes, that requires 
inspections to detect fatigue-related skin cracks and corrosion of the 
skin lap joints in the fuselage upper lobe, and repair, if necessary. 
This amendment also requires modification of certain lap joints and 
inspections of modified lap joints. This amendment is prompted by a 
structural review of Model 747 series airplanes. The actions specified 
by this AD are intended to prevent rapid decompression of the airplane 
and the inability to carry fail-safe loads, due to the problems 
associated with fatigue cracking and corrosion.

DATES: Effective July 13, 1994.
    The incorporation by reference of certain publications listed in 
the regulations is approved by the Director of the Federal Register as 
of July 13, 1994.

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: 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: 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 series 
airplanes was published in the Federal Register on February 24, 1994 
(59 FR 8875). That action proposed to require inspections to detect 
fatigue-related skin cracks and corrosion of the skin lap joints in the 
fuselage upper lobe, and repair, if necessary. That action also 
proposed to require modification of certain lap joints and inspections 
of modified lap joints.
    Interested persons have been afforded an opportunity to participate 
in the making of this amendment. Due consideration has been given to 
the comments received.
    One commenter supports the proposal.
    One commenter requests that proposed inspection requirements be 
revised. This commenter requests that, if the visual inspection 
[proposed in paragraph (a)(1) of the AD] reveals any evidence of 
corrosion, operators should be allowed to perform a low frequency eddy 
current (LFEC) inspection of the entire length of the lap joint to 
determine if corrosion exceeds 10% of the skin thickness. If this LFEC 
inspection is accomplished, the commenter also requests that the visual 
inspection repetitive interval specified in paragraph (a)(1) be 
extended from the proposed 2,000 landings to 3,000 landings so that the 
interval corresponds with other major structural inspection intervals. 
The FAA cannot concur with this request, since the commenter provided 
neither specific inspection instructions nor data to justify the 
effectiveness of the proposed procedures. Under the provisions of 
paragraph (i) of the final rule, however, operators may apply for the 
approval of an alternative method of compliance with the AD, or 
adjustment of the compliance time, if sufficient justification is 
presented to the FAA.
    Two commenters request that proposed paragraph (a) be clarified 
with regard to the inspections and inspection interval required after a 
lap joint has been modified. These commenters request that, for lap 
joints that have been modified by either the full or partial 
modification procedures described in the referenced Boeing service 
bulletin, operators be allowed a period of time during which no 
inspections are required for those lap joints. The referenced Boeing 
service bulletin, as well as proposed paragraph (f), state that post-
modification inspections are to start at 10,000 cycles, 7,000 cycles, 
or 5,000 cycles after modification of the skin lap joints, depending 
upon the type of modification that has been accomplished. However, as 
worded in paragraph (a) of the proposal, the same inspections meant to 
detect cracks and corrosion in unmodified skin lap joints would be 
required to be performed on modified skin lap joints until the 
inspections specified in proposed paragraph (f) begin. The FAA concurs 
that clarification of this requirement is necessary. It was not the 
FAA's intent to require that the initial-type of inspections of 
unmodified lap joints be performed on modified lap joints. Accordingly, 
paragraphs (a)(1) and (a)(3) have been revised to indicate that the 
inspections of the specified lap joints are to continue at repetitive 
intervals only until the lap joints are modified in accordance with the 
requirements of paragraph (e).
    Several commenters request that the compliance time for 
accomplishing the ``full'' modification on certain lap joints, as 
specified in paragraph (b)(2), be extended from the proposed 15 months 
to 18 months. Additionally, these commenters request that the 
compliance time for a similar requirement specified in paragraph (c)(2) 
be extended from the proposed 30 months to 36 months. The commenters 
state that, by extending these compliance times, operators would be 
able to accomplish the modification during a scheduled maintenance 
interval (``C'' check), and thereby eliminate the need to schedule 
special times for the accomplishment of this modification, at 
additional expense. The FAA concurs. It was the FAA's intent that the 
modification be performed at a main base during regularly scheduled 
maintenance where special equipment and trained maintenance personnel 
will be available if necessary. Accordingly, the final rule has been 
revised to specify compliance times as requested by the commenters. The 
FAA has determined that this extension will not adversely affect safety 
since the affected lap joints will be subject to repetitive inspections 
in the interim.
    Two commenters request that paragraph (e) be revised to extend the 
compliance time for accomplishment of the ``full'' modification of the 
specified skin lap joints from the proposed 1,000 cycles (for airplanes 
that have accumulated nearly or more than 20,000 total flight cycles) 
to 4 years after the effective date of the final rule. These commenters 
consider the proposed compliance time to be too short and not 
consistent with compliance times provided for similar actions in other 
AD's pertaining to aging aircraft issues. The FAA does not concur. The 
1,000 flight cycle compliance time is consistent with the mandatory 
modification of a lap joint that has been found to have corrosion or 
cracking, as required by paragraph (b)(2) of this AD. Cold bonded lap 
joints such as these have a history of numerous findings of fatigue 
cracks and corrosion. In light of this, and the fact that fatigue 
cracking is cycle-related, the FAA has determined that modification of 
these lap joints cannot be delayed any further than 1,000 flight 
cycles, especially on those airplanes that already have accumulated 
20,000 flight cycles, without compromising safety.
    One commenter requests that the applicability of proposed 
paragraphs (f)(1), (f)(2), and (f)(3) be revised to clarify that it is 
the ``lap joint,'' rather than the ``airplane,'' on which the 
particular modification has been accomplished. The FAA concurs and has 
revised wording of the final rule to clarify this point.
    One commenter requests that all references in the rule to 
``landings'' be changed to ``cycles.'' The FAA concurs that the 
reference should be revised. The FAA has reviewed the applicable 
service information related to this action and finds that the majority 
of references to recommended compliance times are stated in ``flight 
cycles.'' Although the FAA normally uses the terms ``landings'' and 
``flight cycles'' interchangeably, the FAA considers that it is 
appropriate in this case to change the verbiage of the AD to match that 
of the cited service bulletins. Therefore, in this final rule, the FAA 
has substituted the term ``flight cycles'' for the term ``landings.''
    Another commenter, a non-U.S. operator, requests that the proposed 
rule be revised to include a provision specifying that pressurization 
cycles of 2.0 psi or less need not be counted as a flight cycle when 
determining the number of flight cycles relative to the proposed 
compliance thresholds. This commenter states that a pressurization 
cycle of 2.0 psi or less is a typical pressure used during flight 
training, and causes little fatigue damage of the kind addressed by 
this AD action. The FAA does not concur. The FAA does not consider it 
appropriate to include various provisions in an AD applicable to a 
single operator's unique use of an affected airplane. Paragraph (i) of 
this AD provides for the approval of alternative methods of compliance 
to address these types of unique circumstances. Further, this commenter 
does not compile data for each of its airplanes so that an individual 
airplane's pressurization cycles could be determined; instead, it uses 
a fleet average to calculate the equivalent number of pressurization 
cycles. The FAA does not consider it appropriate to use approximations 
for determining compliance with this AD.
    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 changes previously 
described. The FAA has determined that these changes will neither 
increase the economic burden on any operator nor increase the scope of 
the AD.
    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 will be affected by this proposed AD.
    The required inspections will 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 this 
requirement on U.S. operators is estimated to be $638,000, or $5,500 
per airplane, per inspection.
    The required ``full'' modification will 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 this requirement on 
U.S. operators is estimated to be $61,248,000, or $528,000 per 
airplane.
    The initial high frequency eddy current (HFEC) inspection following 
modification will entail approximately 56 work hours, at an average 
labor rate of $55 per work hour. Based on these figures, the total cost 
impact of this requirement AD on U.S. operators is estimated to be 
$357,280, or $3,080 per airplane.
    Based upon the figures discussed above, the total cost impact of 
this AD on U.S. operators is expected to be $62,243,280, or $536,580 
per airplane. This total cost figure includes the inspections and 
modification, for the first year of the average five-year inspection 
cycle. Additionally, the total cost figure indicated 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.
    The FAA recognizes that the obligation to maintain aircraft in an 
airworthy condition is vital, but sometimes expensive. Because AD's 
require specific actions to address specific unsafe conditions, they 
appear to impose costs that would not otherwise be borne by operators. 
However, because of the general obligation of operators to maintain 
aircraft in an airworthy condition, this appearance is deceptive. 
Attributing those costs solely to the issuance of this AD is 
unrealistic because, in the interest of maintaining safe aircraft, most 
prudent operators would accomplish the required actions even if they 
were not required to do so by the AD.
    A full cost-benefit analysis has not been accomplished for this AD. 
As a matter of law, in order to be airworthy, an aircraft must conform 
to its type design and be in a condition for safe operation. The type 
design is approved only after the FAA makes a determination that it 
complies with all applicable airworthiness requirements. In adopting 
and maintaining those requirements, the FAA has already made the 
determination that they establish a level of safety that is cost-
beneficial. When the FAA, as in this AD, makes a finding of an unsafe 
condition, this means that this cost-beneficial level of safety is no 
longer being achieved and that the required actions are necessary to 
restore that level of safety. Because this level of safety has already 
been determined to be cost-beneficial, a full cost-benefit analysis for 
this AD would be redundant and unnecessary.
    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 
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. 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:

94-12-09  Boeing: Amendment 39-8937. 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 flight cycles 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 panel 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 flight cycles 
until the modification required by paragraph (e) 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 skin 
panel 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 flight cycles 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 skin panel 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 flight cycles 
until the modification required by paragraph (e) 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 18 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 flight cycles after accomplishing the inspection 
during which the corrosion was found, and thereafter at intervals 
not to exceed 500 flight cycles until the ``full'' modification 
required by paragraph (c)(2) of this AD is accomplished: Perform a 
HFEC inspection to detect cracks of the corroded skin panel lap 
joint, in accordance with the service bulletin.
    (2) Within 36 months after accomplishing the inspection during 
which the corrosion was found: Accomplish the ``full'' modification 
in accordance with the service bulletin.
    (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 flight cycles, or within the next 1,000 
flight cycles 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 panel 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. Accomplishment of this 
modification terminates the repetitive inspection requirements of 
paragraph (a) of this AD.
    (1) For airplane line numbers 001 through 058, inclusive: Modify 
the skin panel 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 panel 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 panel 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 flight cycles.
    (1) For skin panel lap joints on which the ``full'' modification 
has been accomplished: Within 10,000 flight cycles after 
accomplishment of that modification.
    (2) For skin panel lap joints on which the ``optional'' 
(partial) modification has been accomplished: Within 7,000 flight 
cycles after accomplishment of that modification.
    (3) For skin panel lap joints 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 flight cycles 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 skin panel 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 
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.
    (k) The actions shall be done in accordance with Boeing Service 
Bulletin 747-53-2307, Revision 2, dated October 14, 1993. 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.
    (l) This amendment becomes effective on July 13, 1994.

    Issued in Renton, Washington, on June 2, 1994.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 94-13852 Filed 6-10-94; 8:45 am]
BILLING CODE 4910-13-P