[Federal Register Volume 59, Number 219 (Tuesday, November 15, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-26874]
[[Page Unknown]]
[Federal Register: November 15, 1994]
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DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Part 39
[Docket No. 94-NM-30-AD; Amendment 39-9057; AD 94-22-08]
Airworthiness Directives; Boeing Model 747 Series Airplanes
Equipped With General Electric CF6 Series Engines
AGENCY: Federal Aviation Administration, DOT.
ACTION: Final rule.
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SUMMARY: This amendment supersedes an existing airworthiness directive
(AD), applicable to certain Boeing Model 747 series airplanes, that
currently requires inspections of the strut skin in the area of the
precooler exhaust vent for cracks on the inboard and outboard struts,
and repair, if necessary. This amendment requires inspections of an
expanded area for certain airplanes, and inspections of airplanes on
which a skin doubler has been installed as terminating action for the
existing AD. This amendment is prompted by reports of strut skin
fatigue cracks and heat damage found aft of the edges of skin doublers
installed on certain Model 747 series airplanes. The actions specified
by this AD are intended to prevent separation of an engine due to
overheating and subsequent cracking of the engine strut.
DATES: Effective December 15, 1994.
The incorporation by reference of certain publications listed in
the regulations is approved by the Director of the Federal Register as
of December 15, 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: Tim Backman, Aerospace Engineer,
Airframe Branch, ANM-120S, FAA, Transport Airplane Directorate, Seattle
Aircraft Certification Office, 1601 Lind Avenue SW., Renton, Washington
98055-4056; telephone (206) 227-2776; fax (206) 227-1181.
SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal
Aviation Regulations (14 CFR part 39) by superseding AD 87-04-21,
amendment 39-5543 (52 FR 3793, February 6, 1987), which is applicable
to certain Boeing Model 747 series airplanes, was published in the
Federal Register on June 14, 1994 (59 FR 30543). The action proposed to
require, for certain airplanes, repetitive visual inspections to detect
cracks, heat discoloration, or wrinkles of the strut skin and internal
structure in the area of the precooler exhaust vent from nacelle
station (NAC STA) 230 to NAC STA 300 in the inboard and outboard struts
of certain airplanes, or in the area of the precooler exhaust vent from
the edge of the skin doubler to NAC STA 300 in the inboard and outboard
struts of certain other airplanes, and repair, if necessary.
Interested persons have been afforded an opportunity to participate
in the making of this amendment. Due consideration has been given to
the comments received.
Two commenters support the proposed rule.
One commenter, Boeing, requests that the aft limit of the
inspection zones specified in paragraphs (b) and (c) of the proposal be
changed from NAC STA 300 to NAC STA 286. The commenter indicates that
expansion of the inspection zone to NAC STA 300 was based on one report
of a blown duct. This incident was reported immediately. The commenter
contends that the damage that occurred was the result of a system
malfunction and, therefore, inspection should not be required beyond
NAC STA 286. In light of this information, the FAA concurs with the
commenter's request. Paragraphs (b) and (c) and NOTES 1 and 2 of the
final rule have been revised to indicate that the aft limit of the
expanded inspection zone only extends to NAC STA 286.
This commenter also requests that the FAA revise paragraph (c) of
the proposed rule to exclude airplanes on which a large doubler was
installed during production (airplane line numbers 587 and subsequent).
The applicability of proposed paragraph (c) includes airplanes modified
during production or in accordance with Boeing Service Bulletin 747-54-
2091. The commenter notes that for 12 years there have been no in-
service problems aft of the existing doubler to beyond NAC STA 286. The
commenter also states that the Maintenance Review Board (MRB) report
recommends a visual inspection of the strut side skin during regularly
scheduled ``C'' checks. The commenter adds that, for airplanes
retrofitted in service, data show that heat damage occurred in the area
between NAC STA 270 and NAC STA 286 prior to installation of the
doubler. The commenter states that one small crack has been reported
aft of the large replacement doubler installed in accordance with
Boeing Service Bulletin 747-54-2091; however, that crack is believed to
have occurred as a result of previous damage.
The FAA does not concur with the commenter's request. This AD was
prompted by reports of skin cracks and heat damage found aft of the
edges of doublers installed in accordance with Boeing Service Bulletin
747-54-2091. The doubler configuration installed during production of
these airplanes is identical to that installed in accordance with
Boeing Service Bulletin 747-54-2091. The FAA finds that, regardless of
whether the doubler was installed during production or in accordance
with the Boeing service bulletin, cracking can occur in the subject
area and the inspection of the expanded area specified in paragraph (c)
of this AD must be accomplished on both groups of airplanes to ensure
that the unsafe condition is positively addressed.
The commenter requests that the compliance times specified in
paragraph (c) of the proposed rule be revised from 120 days to 15
months. Paragraph (c) of the proposal would require a visual inspection
to detect cracks, heat discoloration, or wrinkles of the strut skin and
internal structure in the area of the precooler exhaust vent from the
edge of the doubler to NAC STA 300 on the inboard and outboard struts
of certain airplanes and on the outboard struts of other airplanes. The
commenter states that service data indicate that, for airplanes on
which either no doubler or a temporary doubler has been installed, no
stringer cracking has occurred in the presence of large skin cracks
forward of NAC STA 270. The commenter explains that, for the outboard
strut, skin stresses aft of NAC STA 270 are lower due to increased
thickness of the skin and, if cracking should occur, the crack growth
rate would be low. The commenter also notes that the MRB report
recommends detailed visual inspections of the side skin at every ``C''
check interval, which is approximately every 15 months. In addition,
the commenter states that service history amplifies the fact that zero
time reinforcement of the side skin during the production stage
forestalls primary damage to the adjacent skin.
The FAA does not concur with the commenter's request. The FAA has
received reports of softening of the skin aft of the large doubler end
at NAC STA 270 on both the inboard and the thicker-skinned outboard
struts due to overheating. The FAA also has received reports of
cracking in multiple fastener holes in that area of the struts. In
light of these reports, the FAA has determined that 120 days represents
the maximum interval of time allowable wherein the inspection can
reasonably be accomplished and an acceptable level of safety can be
maintained.
For the same reasons given as justification for its previous
request, the commenter also requests that the compliance time specified
in paragraph (b)(2) of the proposal be extended from 12 to 15 months.
The commenter adds that the struts on these airplanes were designed to
handle 3g side loads, which is well above normal operating loads.
The FAA does not concur with the commenter's request. AD 87-04-21
required inspections of the strut in accordance with Revision 1 of
Boeing Service Bulletin 747-54-2091; however, that revision of the
service bulletin does not specify procedures for inspections of the
internal structure of the strut. The FAA has received numerous reports
of cracked stiffeners due to heat damage; such cracks could only be
seen during an inspection of the internal structure, as required by
paragraph (b) of this AD. In light of these reports, and in
consideration of the degree of urgency associated with addressing the
subject unsafe condition, the FAA has determined that the compliance
time, as proposed, represents the maximum interval in which the
inspections can be accomplished in a timely manner within the fleet and
still maintain an adequate level of safety.
The commenter requests that paragraphs (b) and (c) of the proposal
be revised to remove the requirement to perform inspections of the
internal structure of the strut from NAC STA 270 to NAC STA 286. The
commenter references its justification for the previous two comments.
The commenter adds that service history indicates that cracking will
develop in the strut skin before it will develop in the strut stiffener
or frame structure in this area. In addition, since service history
demonstrates that stringer cracks are preceded by skin cracks, the
commenter believes it is reasonable to expect that any sizable stringer
damage will be found if a skin crack is observed during a visual
inspection. The commenter adds that operators have the option to
inspect internally at routine intervals.
The FAA does not concur. The FAA has received reports of skin
cracking that has been associated with cracked stiffeners (internal
structure) in the area forward of NAC STA 270. Although the skin is
thicker aft of NAC STA 270 than forward of it, skin cracks have been
found aft of NAC STA 270 that could likely be associated with stiffener
cracks. Some skin cracking also initiated in multiple fastener holes in
the area from NAC STA 270 to NAC STA 286 due to heat damage. In light
of these reports, the FAA has determined that, in order to provide an
acceptable level of safety, detailed visual inspections of the internal
structure of the strut from NAC STA 270 to NAC STA 286 are necessary to
detect possible damage in that area.
The same commenter requests that paragraph (e) of the proposed rule
be revised to allow continued flight with a skin crack, heat
discoloration, wrinkle, or previously stop-drilled crack in the
precooler exhaust, provided that the length of the crack does not
exceed one inch. The commenter indicates that service history
demonstrates that some degree of damage is acceptable with continued
monitoring inspections at an interval of 15 months. The commenter
states that suspected heat damage of the side skin can be verified by
conductivity checks. In addition, standard industry practice allows
wrinkles to be two times the thickness (depending on design) and stop-
drilling holes to slow crack growth as a time-limited repair. The
commenter considers the time-limited repair acceptable for a maximum
period of 18 months.
The FAA does not concur. The FAA has issued a number of AD's that
address cracking and corrosion of lugs, links, fuse pins, and webs on
the struts of Model 747 series airplanes [for example, AD 93-17-07,
amendment 39-8678 (58 FR 45827, August 31, 1993); AD 92-24-51,
amendment 39-8439 (57 FR 60118, December 18, 1992); and AD 86-07-06,
amendment 39-5270 (51 FR 10821, March 31, 1986)]. In some cases where
the structure surrounding the previously stop-drilled crack, the skin
crack, heat discoloration, or wrinkle is shown by service history to be
free from cracks and corrosion, continued flight without repair of
these items may have been acceptable. However, in light of the numerous
problems associated with the strut on these airplanes, continued flight
without repair of previously stop-drilled cracks, skin cracks, heat
discoloration, or wrinkles cannot be allowed in the case of this AD
without compromising the continued operational safety of the affected
airplanes. However, the FAA would consider a request for an adjustment
of the compliance time, in accordance with the provision of paragraph
(g) of this AD, provided that appropriate justification accompanies the
request.
The manufacturer has advised that it is currently developing a
modification program for the engine strut that will positively address
the unsafe condition addressed by this AD. Once this modification
program is developed, approved, and available, the FAA may consider
additional rulemaking.
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 250 Model 747 series airplanes of the
affected design in the worldwide fleet. The FAA estimates that 4
airplanes of U.S. registry will be affected by this AD.
The inspections that were required previously by AD 87-04-21, and
retained in this AD, take approximately 4 work hours per airplane to
accomplish, at an average labor rate of $55 per work hour. Based on
these figures, the total cost impact of that inspection requirement on
U.S. operators is estimated to be $880, or $220 per airplane.
The new inspections that will be added by this new AD action will
take approximately 4 work hours per airplane to accomplish, at an
average labor rate of $55 per work hour. Based on these figures, the
total cost impact of the new inspection requirements of this AD on U.S.
operators is estimated to be $880, or $220 per airplane.
The total cost impact figure discussed above 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 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 removing amendment 39-5543 (52 FR
3793, February 6, 1987), and by adding a new airworthiness directive
(AD), amendment 39-9057, to read as follows:
94-22-08 Boeing: Amendment 39-9057. Docket 94-NM-30-AD. Supersedes
AD 87-04-21, Amendment 39-5543.
Applicability: Model 747 series airplanes equipped with General
Electric CF6 series engines, certificated in any category.
Compliance: Required as indicated, unless accomplished
previously.
To prevent separation of an engine due to overheating and
subsequent cracking of the engine strut, accomplish the following:
(a) For airplanes listed in Boeing Service Bulletin 747-54-2091,
Revision 1, dated October 22, 1984: Prior to the accumulation of
10,000 total hours time-in-service, or within the next 7\1/2\ months
after March 13, 1987 (the effective date of AD 87-04-21, Amendment
39-5543), whichever occurs later, perform a visual inspection to
detect cracks of the strut skin in the area of the precooler exhaust
vent on the inboard and outboard struts of Group 1 airplanes, and on
the outboard struts of Group 2 airplanes, as defined in the service
bulletin, in accordance with Boeing Service Bulletin 747-54-2091,
Revision 1, dated October 22, 1984; Revision 2, dated March 24,
1988; Revision 3, dated July 27, 1989; Revision 4, dated December
14, 1989; or Revision 5, dated April 26, 1990. After the effective
date of this AD, the inspection shall be accomplished in accordance
with paragraph (b) of this AD.
(1) If no crack is found, repeat the inspection required by
paragraph (a) of this AD thereafter at intervals not to exceed 15
months, until the inspection required by paragraph (b) or (c) of
this AD, as applicable, is accomplished.
(2) If any crack is found, prior to further flight, repair in
accordance with FAA-approved data, and repeat the inspection
required by paragraph (a) of this AD thereafter at intervals not to
exceed 15 months, until the inspection required by paragraph (b) or
(c) of this AD, as applicable, is accomplished.
(b) For airplanes on which a frame stiffener and a skin doubler
have not been installed during production or in accordance with
Boeing Service Bulletin 747-54-2091, Revision 1, dated October 22,
1984; Revision 2, dated March 24, 1988; Revision 3, dated July 27,
1989; Revision 4, dated December 14, 1989; or Revision 5, dated
April 26, 1990: Perform a visual inspection to detect cracks, heat
discoloration, or wrinkles of the strut skin and internal structure
in the area of the precooler exhaust vent from nacelle station (NAC
STA) 230 to NAC STA 286 on the inboard and outboard struts of Group
1 airplanes and on the outboard struts of Group 2 airplanes, in
accordance with the inspection procedures described in Figure 3 of
Boeing Service Bulletin 747-54-2091, Revision 5, dated April 26,
1990; at the time specified in paragraph (b)(1) or (b)(2) of this
AD, whichever occurs later. Accomplishment of this inspection
terminates the repetitive inspections required by paragraph (a) of
this AD.
(1) Prior to the accumulation of 10,000 total hours time-in-
service on the airplane strut, or within 120 days after the
effective date of this AD, whichever occurs later. Or
(2) Within 12 months after the immediately preceding inspection
accomplished in accordance with paragraph (a) of this AD.
Note 1: Paragraph (b) of this AD specifies an inspection zone
that is expanded beyond the zone described in Revision 5 of the
service bulletin to cover a 30-inch width from NAC STA 230 to NAC
STA 286.
(c) For airplanes on which a frame stiffener and a skin doubler
have been installed during production or in accordance with Boeing
Service Bulletin 747-54-2091, Revision 1, dated October 22, 1984;
Revision 2, dated March 24, 1988; Revision 3, dated July 27, 1989;
Revision 4, dated December 14, 1989; or Revision 5, dated April 26,
1990: Within 120 days after the effective date of this AD, perform a
visual inspection to detect cracks, heat discoloration, or wrinkles
of the strut skin and internal structure in the area of the
precooler exhaust vent from the edge of the doubler to NAC STA 286
on the inboard and outboard struts of Group 1 airplanes and on the
outboard struts of Group 2 airplanes, in accordance with the
inspection procedures described in Figure 3 of Boeing Service
Bulletin 747-54-2091, Revision 5, dated April 26, 1990.
Note 2: Paragraph (c) of this AD specifies an inspection zone
that is expanded beyond the zone described in Revision 5 of the
service bulletin to cover a 30-inch width from the doubler edge to
NAC STA 286.
(d) If no crack, heat discoloration, or wrinkle is found during
the inspection required by paragraph (b) or (c) of this AD, repeat
that inspection thereafter at intervals not to exceed 15 months.
(e) If any crack, heat discoloration, wrinkle, or previously
stop-drilled crack is found during the inspection required by
paragraph (b) or (c) of this AD, prior to further flight, repair
using either the small skin doubler and frame stiffener or the large
skin doubler and frame stiffener specified in Boeing Service
Bulletin 747-54-2901, Revision 5, dated April 26, 1990, in
accordance with that service bulletin; or in accordance with a
method approved by the Manager, Seattle Aircraft Certification
Office (ACO), FAA, Transport Airplane Directorate. Thereafter,
repeat that inspection at intervals not to exceed 15 months.
(f) Installation of a frame stiffener and a skin doubler
referred to in Boeing Service Bulletin 747-54-2091 as ``terminating
action'' does not constitute terminating action for the inspection
requirements of this AD.
(g) 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 3: Information concerning the existence of approved
alternative methods of compliance with this AD, if any, may be
obtained from the Seattle ACO.
(h) 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.
(i) The actions shall be done in accordance with the following
Boeing service bulletins, which contain the specified effective
pages:
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Revision
Service Bulletin referenced and date - Page number level shown Date shown on page
on page
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747-54-2091, Revision 1, October 22, 1984................... 1, 3-12-..... 1-........... October 22, 1984.
2, 13-20-.... Original-.... January 27, 1984.
747-54-2091, Revision 2, March 24, 1988-.................... 1, 4-37-..... 2-........... March 31, 1988.
- 2-........... Original-.... January 27, 1984.
- 3-........... 1-........... October 22, 1984.
747-54-2091, Revision 3, July 27, 1989-..................... 1-24, 26-36-. 3-........... July 27, 1989.
- 25-.......... 2-........... March 31, 1988.
747-54-2091, Revision 4, December 14, 1989-................. 1-5-......... 4-........... December 14, 1989.
- 6-24, 26-36-. 3-........... July 27, 1989.
- 25-.......... 2-........... March 31, 1988.
747-54-2091, Revision 5, April 26, 1990-.................... 1-38-........ 5-........... April 26, 1990.
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The incorporation by reference of these documents 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.
(j) This amendment becomes effective on December 15, 1994.
Issued in Renton, Washington, on October 25, 1994.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. 94-26874 Filed 11-14-94; 8:45 am]
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