[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