[Federal Register Volume 61, Number 50 (Wednesday, March 13, 1996)]
[Proposed Rules]
[Pages 10294-10296]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-5943]



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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 96-NM-04-AD]


Airworthiness Directives; Boeing Model 737-100 and -200 Series 
Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the adoption of a new airworthiness 
directive (AD) that is applicable to certain Boeing Model 737-100 and -
200 series airplanes. This proposal would require inspections to detect 
cracking of the support fittings of the Krueger flap actuator; and 
replacement of existing fittings with new steel fittings and 
modification of the aft attachment of the actuator, if necessary. This 
proposal 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 the proposed 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: Comments must be received by May 6, 1996.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-103, 
Attention: Rules Docket No. 96-NM-04-AD, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056. Comments may be inspected at this location 
between 9:00 a.m. and 3:00 p.m., Monday through Friday, except Federal 
holidays.
    The service information referenced in the proposed rule may be 
obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, 
Washington 98124-2207. This information may be examined at the FAA, 
Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, 
Washington.

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:

Comments Invited

    Interested persons are invited to participate in the making of the 
proposed rule by submitting such written data, views, or arguments as 
they may desire. Communications shall identify the Rules Docket number 
and be submitted in triplicate to the address specified above. All 
communications received on or before the closing date for comments, 
specified above, will be considered before taking action on the 
proposed rule. The proposals contained in this notice may be changed in 
light of the comments received.
    Comments are specifically invited on the overall regulatory, 
economic, environmental, and energy aspects of the proposed rule. All 
comments submitted will be available, both before and after the closing 
date for comments, in the Rules Docket for examination by interested 
persons. A report summarizing each FAA-public contact concerned with 
the substance of this proposal will be filed in the Rules Docket.
    Commenters wishing the FAA to acknowledge receipt of their comments 
submitted in response to this notice must submit a self-addressed, 
stamped postcard on which the following statement is made: ``Comments 
to Docket Number 96-NM-04-AD.'' The postcard will be date stamped and 
returned to the commenter.

Availability of NPRMs

    Any person may obtain a copy of this NPRM by submitting a request 
to the FAA, Transport Airplane Directorate, ANM-103, Attention: Rules 
Docket No. 96-NM-04-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    The FAA received several reports indicating that cracking was found 
on Model 737 series airplanes in the support fittings that attach the 
Krueger flap actuator to the front spar. This cracking was found in the 
actuator attach lugs of the support fittings on a number of airplanes, 
and in the fillet radius between the actuator attach lug and the 
vertical flanges of the fitting on one airplane. The cause of the 
cracking has been attributed to fatigue and stress corrosion. Complete 
fracture of both actuator attach lugs could allow the actuator to 
separate from the support fitting, which could sever the hydraulic 
lines and result in the loss of hydraulic fluids. This condition, if 
not corrected, could result in possible failure of one or more 
hydraulic systems, and subsequent reduced controllability of the 
airplane.
    The FAA also received two reports indicating that hydraulic system 
A and the standby hydraulic system failed during flight on Model 737 
series airplanes. During subsequent emergency landings, these airplanes 
departed the end of the runway and sustained severe damage. On one of 
these airplanes, both actuator attach lugs on the support fittings of 
the No. 1 Krueger flap actuator were severed completely. The actuator 
separated from the front spar and the adjacent hydraulic lines were 
severed. On the other airplane, the No. 3 Krueger flap actuator 
separated from the fitting and the hydraulic lines to the actuator were 
severed. Subsequently, the hydraulic fuse did not close sufficiently to 
prevent the loss of hydraulic fluid from the system. Results of a 
laboratory examination of the fuse indicated that corrosion existed on 
the magnesium piston of the fuse.
    The FAA has reviewed and approved 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. This 
service bulletin describes procedures for an initial visual inspection 
and repetitive eddy current inspections to detect cracking of the 
support fittings of the Krueger flap actuator; and replacement of 
existing fittings with new steel fittings and modification of the aft 
attachment of the actuator, if necessary. Such replacement and 
modification eliminates the need for repetitive eddy current 
inspections of the fittings.
    Since an unsafe condition has been identified that is likely to 
exist or develop on other products of this same type design, the 
proposed AD would require repetitive eddy current inspections to detect 
cracking of the support fittings of the Krueger flap actuator; and 
replacement of existing fittings with new steel fittings and 
modification of the aft attachment of the actuator, if necessary. Such 
replacement

[[Page 10295]]
and modification, if accomplished, would constitute terminating action 
for the required repetitive inspections. The actions would be required 
to be accomplished in accordance with the service bulletin described 
previously.
    Operators should note that, while the service bulletin recommends 
that the initial inspection be performed using a visual method and 
subsequent repetitive inspections be performed using an eddy current 
technique, this proposed AD would require that both the initial and 
repetitive inspections be accomplished using the eddy current method. 
The support fittings of the Krueger flap actuator are susceptible to 
stress corrosion cracking, and the crack growth rate for such cracking 
is unknown. The FAA finds that, if a visual inspection is accomplished 
to detect cracking of the support fittings, such cracking may not be 
detected in a timely manner to adequately address the unsafe condition. 
Therefore, the FAA has determined that an adequate level of safety for 
the affected fleet requires that both the initial and repetitive 
inspections of these fittings be performed using an eddy current 
technique, which is a more reliable method of crack detection.
    The FAA is considering the issuance of separate rulemaking action 
to address failure of hydraulic fuses having magnesium pistons. Fuses 
of this type are installed on Model 747-100, -200, -300, and -SP series 
airplanes, as well as Model 737-100 and -200 series airplanes.
    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 would be affected by this proposed AD, 
that it would take approximately 12 work hours per airplane (6 work 
hours per wing) to accomplish the proposed actions, and that the 
average labor rate is $60 per work hour. Based on these figures, the 
cost impact of the proposed 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 proposed requirements of 
this AD action, and that no operator would accomplish those actions in 
the future if this AD were not adopted.
    Should an operator elect to accomplish the replacement and 
modification rather than continue the repetitive inspections, it would 
take approximately 88 work hours per airplane (44 work hours per wing) 
to accomplish the replacement and modification, at an average labor 
rate of $60 per work hour. Required parts would cost approximately 
$13,172 per airplane. Based on these figures, the cost impact of the 
replacement and modification is estimated to be $18,452 per airplane.
    The regulations proposed herein would 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 
proposal would not have sufficient federalism implications to warrant 
the preparation of a Federalism Assessment.
    For the reasons discussed above, I certify that this proposed 
regulation (1) is not a ``significant regulatory action'' under 
Executive Order 12866; (2) is not a ``significant rule'' under the DOT 
Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); 
and (3) if promulgated, 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 copy of the draft 
regulatory evaluation prepared for this action is contained in the 
Rules Docket. A copy of it may be obtained by contacting the Rules 
Docket at the location provided under the caption ``ADDRESSES.''

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation Administration proposes to amend 
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:

Boeing: 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.


[[Page 10296]]

    Issued in Renton, Washington, on March 7, 1996.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 96-5943 Filed 3-12-96; 8:45 am]
BILLING CODE 4910-13-U