[Federal Register Volume 61, Number 157 (Tuesday, August 13, 1996)]
[Rules and Regulations]
[Pages 41957-41959]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-20426]
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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39
[Docket No. 96-NM-04-AD; Amendment 39-9712; AD 96-17-04]
RIN 2120-AA64
Airworthiness Directives; Boeing Model 737-100 and -200 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 737-100 and -200 series airplanes,
that requires inspections to detect cracking of the support fittings of
the Krueger flap actuator and, if necessary, replacement of existing
fittings with new steel fittings and modification of the aft attachment
of the actuator. This amendment is prompted by reports of cracking due
to fatigue and stress corrosion of the support fittings of the Krueger
flap actuator. The actions specified by this AD are intended to prevent
such cracking, which could result in fracturing of the actuator attach
lugs, separation of the actuator from the support fitting, severing of
the hydraulic lines, and resultant loss of hydraulic fluids. These
conditions, if not corrected, could result in possible failure of one
or more hydraulic systems, and subsequent reduced controllability of
the airplane.
DATES: Effective September 17, 1996.
The incorporation by reference of certain publications listed in
the regulations is approved by the Director of the Federal Register as
of September 17, 1996.
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: Della Swartz, Aerospace Engineer,
Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office,
1601 Lind Avenue, SW., Renton, Washington; telephone (206) 227-2785;
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 737-100 and -
200 series airplanes was published in the Federal Register on March 13,
1996 (61 FR 10294). That action proposed to require inspections to
detect cracking of the support fittings of the Krueger flap actuator
and, if necessary, replacement of existing fittings with new steel
fittings and modification of the aft attachment of the actuator.
Interested persons have been afforded an opportunity to participate
in the making of this amendment. Due consideration has been given to
the comments received.
Support for the Proposal
One commenter supports the proposal.
Request to Revise Proposed Inspection Requirements
The Air Transport Association (ATA), on behalf of its member
operators, requests that the proposed requirement to perform repetitive
eddy current inspections be replaced with a requirement to perform
close visual inspections at 3,000-flight hour intervals, followed by an
eddy current inspection or replacement of the fitting within a 4-year
period. This commenter maintains that this alternative inspection
program is:
1. More consistent with the recommendations of the airframe
manufacturer;
2. Equivalent in safety to that proposed in the notice; and
3. More cost effective.
Further, this commenter states that, while the proposed eddy
current inspection may be viewed as a more critical inspection process,
it is not necessary to respond to the airworthiness concern. This
commenter contends that, in order to determine whether a more stringent
process is required (i.e., more stringent than the manufacturer's
recommendations), the FAA should review service history data to
determine whether cracking of the subject support fittings has actually
become a fleet-wide problem. The commenter maintains that, while the
one incident described in the preamble to the notice was certainly of
concern, there is insufficient data to indicate that cracked support
fittings is an industry problem.
The FAA does not concur. As explained in the preamble to the
notice, the subject cracking in the fittings is attributed to stress
corrosion combined with fatigue. The crack growth rate for such
cracking is not known; however, it is known that material that the
fitting is made from, 7075-T6 aluminum, is highly susceptible to stress
corrosion cracking and has low toughness. It is also known that the
critical crack size for this fitting is 0.165 inch. Cracks of this
small size cannot be found with a high degree of confidence using a
visual inspection technique. An eddy current inspection is a much more
reliable method of finding such small cracks.
As for the service history of the subject problem, there have been
several reports of cracking found in actuator attach support fitting
assemblies on a number of in-service Model 737 series airplanes. There
also have been two accidents involving hydraulic system failures that
were associated with the failure of the actuator attach lugs on the
support fittings. The FAA considers this a sufficient amount of service
history to demonstrate that a potential unsafe condition associated
with the subject cracking exists in airplanes equipped with the subject
fittings.
In light of the small critical crack size, the high susceptibility
to stress corrosion cracking of 7075-T6 material, and the ample service
history relative to the addressed unsafe condition, the FAA does not
find that the commenter's suggested alternative inspection program
would provide an acceptable level of safety compared to that required
by this final rule.
[[Page 41958]]
Request to Revise Proposed Inspection Intervals
One commenter requests that the proposed inspections be required in
terms of flight cycles, rather than in terms of time-in-service. The
commenter states that, because fatigue cracking of the actuator support
fitting is caused by cycling of the Krueger flap, the maximum
inspection intervals should be limited by flight cycles, not flight
hours.
The FAA does not concur. The cracking mechanism associated with the
addressed problem is stress corrosion cracking combined with fatigue.
Although the commenter is correct that fatigue is cycle-driven, stress
corrosion cracking is time-or flight hour-driven, since it is caused by
a sustained tensile stress in a corrosive environment. Therefore, the
FAA finds that a flight hour (time-in-service) inspection interval is
appropriate for these inspections.
Conclusion
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 as proposed.
Cost Impact
There are approximately 727 Model 737-100 and -200 series airplanes
of the affected design in the worldwide fleet. The FAA estimates that
270 airplanes of U.S. registry will be affected by this AD, that it
will take approximately 12 work hours per airplane (6 work hours per
wing) to accomplish the required actions, and that the average labor
rate is $60 per work hour. Based on these figures, the cost impact of
the AD on U.S. operators is estimated to be $194,400, or $720 per
airplane, per inspection.
The 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.
Regulatory Impact
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. 106(g), 40113, 44701.
Sec. 39.13 [Amended]
2. Section 39.13 is amended by adding the following new
airworthiness directive:
96-17-04 Boeing: Amendment 39-9712. Docket 96-NM-04-AD.
Applicability: Model 737-100 and -200 series airplanes, line
positions 001 through 813 inclusive, certificated in any category.
Note 1: This AD applies to each airplane identified in the
preceding applicability provision, regardless of whether it has been
otherwise modified, altered, or repaired in the area subject to the
requirements of this AD. For airplanes that have been modified,
altered, or repaired so that the performance of the requirements of
this AD is affected, the owner/operator must request approval for an
alternative method of compliance in accordance with paragraph (d) of
this AD. The request should include an assessment of the effect of
the modification, alteration, or repair on the unsafe condition
addressed by this AD; and, if the unsafe condition has not been
eliminated, the request should include specific proposed actions to
address it.
Compliance: Required as indicated, unless accomplished
previously.
To prevent possible failure of one or more hydraulic systems and
subsequent reduced controllability of the airplane, accomplish the
following:
(a) Within one year after the effective date of this AD, perform
an eddy current inspection to detect cracking of the support fitting
of the Krueger flap actuator, in accordance with Boeing Service
Bulletin 737-57-1129, Revision 1, dated October 30, 1981, as revised
by Notices of Status Change 737-57-1129NSC1, dated July 23, 1982;
737-57-1129 NSC2, dated April 14, 1983; and 737-57-1129 NSC 3, dated
May 18, 1995.
(1) If no cracking is found, repeat the inspection required by
paragraph (a) of this AD thereafter at intervals not to exceed 3,000
hours time-in-service.
(2) If any cracking is found, prior to further flight,
accomplish the replacement and modification specified in paragraph
(b) of this AD.
(b) Replacement of the support fitting with a steel fitting and
modification of the actuator aft attachment in accordance with
Boeing Service Bulletin 737-57-1129, Revision 1, dated October 30,
1981, as revised by Notices of Status Change 737-57-1129NSC1, dated
July 23, 1982; 737-57-1129 NSC2, dated April 14, 1983; and 737-57-
1129 NSC 3, dated May 18, 1995; constitutes terminating action for
the repetitive inspections required by this AD.
(c) As of the effective date of this AD, no person shall install
a support fitting having part number 69-37892-9, 69-37892-10, 69-
37893-1, or 69-37893-2 on the Krueger flap actuator of any airplane.
(d) An alternative method of compliance or adjustment of the
compliance time that provides an acceptable level of safety may be
used if approved by the Manager, Seattle Aircraft Certification
Office (ACO), FAA, Transport Airplane Directorate. Operators shall
submit their requests through an appropriate FAA Principal
Maintenance Inspector, who may add comments and then send it to the
Manager, Seattle ACO.
Note 2: Information concerning the existence of approved
alternative methods of compliance with this AD, if any, may be
obtained from the Seattle ACO.
(e) Special flight permits may be issued in accordance with
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.
(f) The inspections, replacement, and modification shall be done
in accordance with Boeing Service Bulletin 737-57-1129, Revision 1,
dated October 30, 1981, as revised by Notice of Status Change 737-
57-1129NSC1, dated July 23, 1982; Notice of Status Change 737-57-
1129 NSC2, dated April 14, 1983; and Notice of Status Change 737-57-
1129 NSC 3, dated May 18, 1995. 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.
(g) This amendment becomes effective on September 17, 1996.
[[Page 41959]]
Issued in Renton, Washington, on August 6, 1996.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification
Service.
[FR Doc. 96-20426 Filed 8-12-96; 8:45 am]
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