[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]
BILLING CODE 4910-13-U