Airworthiness Directives; Boeing Model 737-100, -200, -300, -400, and -500 Series Airplanes

[Federal Register Volume 64, Number 91 (Wednesday, May 12, 1999)]
[Rules and Regulations]
[Pages 25424-25426]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-11784]



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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 99-NM-68-AD; Amendment 39-11165; AD 99-10-12]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737-100, -200, -300, -400, 
and -500 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule; request for comments.

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SUMMARY: This amendment supersedes an existing airworthiness directive 
(AD), applicable to certain Boeing Model 737-100, -200, -300, -400, and 
-500 series airplanes, that currently requires repetitive inspections 
to detect cracking, plating degradation, and corrosion of the main 
landing gear (MLG) actuator beam arms and actuator beam attach bolts; 
and rework or replacement, if necessary. The existing AD also provides 
for optional terminating action for the repetitive inspections. This 
amendment removes the requirement to inspect the actuator beam attach 
bolts, expands the applicability of the existing AD to include 
additional airplanes, and removes the optional terminating action. This 
amendment is prompted by reports of cracked MLG actuator beam arms. The 
actions specified in this AD are intended to detect and correct 
corrosion and cracking of the MLG actuator beam arm, which could result 
in damage to the control cables for the aileron and spoiler and 
consequent reduced controllability of the airplane.

DATES: Effective May 27, 1999.
    The incorporation by reference of certain publications listed in 
the regulations is approved by the Director of the Federal Register as 
of May 27, 1999.
    Comments for inclusion in the Rules Docket must be received on or 
before July 12, 1999.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 99-NM-68-AD, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056.
    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 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.

FOR FURTHER INFORMATION CONTACT: Rick Kawaguchi, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA, Transport Airplane Directorate, Seattle 
Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056; telephone (425) 227-1153; fax (425) 227-1181.

SUPPLEMENTARY INFORMATION: On February 13, 1991, the FAA issued AD 91-
05-16, amendment 39-6913 (56 FR 7561, February 25, 1991), applicable to 
certain Boeing Model 737-100, -200, -300, -400, and -500 series 
airplanes. That AD requires repetitive visual and ultrasonic 
inspections of the main landing gear (MLG) actuator beam arms and 
actuator beam attach bolts for cracking, plating degradation, and 
corrosion; and rework or replacement, if necessary. The existing AD 
also provides for optional terminating action for the repetitive 
inspections. That action was prompted by reports of failure of the 
actuator beam arm and trunnion pin due to corrosion. The actions 
required by that AD are intended to prevent structural damage and 
severing of control cables and hydraulic tubing in this area, which 
could result in reduced controllability of the airplane.

Actions Since Issuance of Previous Rule

    Since the issuance of that AD, the FAA has received reports of 
cracking of an actuator beam arm on the MLG on three Boeing Model 737-
300 series airplanes. Two operators reported damage to the landing 
gear, wing structure, fluid lines, and aileron and spoiler control 
cables; the damage has been attributed to fractures of the MLG actuator 
beam arm. One of those operators subsequently conducted a fleet-wide 
inspection and found a cracked actuator beam arm on another airplane. 
The beam arm fractures originated from corrosion pits in the actuator 
beam arm clevis. All three fractured actuator beam arms had been 
reworked in accordance with AD 91-05-16. In one case, the fracture 
occurred 7 years (at approximately 13,500 flight cycles) after 
completion of the terminating action in compliance with that AD.

FAA's Conclusions

    The FAA has determined that rework or replacement of the actuator 
beam arm, which AD 91-05-16 provides as either optional corrective 
action or optional terminating action for the repetitive inspections, 
does not adequately prevent corrosion and subsequent cracking of the 
clevis area. Therefore, the FAA finds that, to ensure the continued 
safety of the fleet, it is necessary to require that repetitive 
inspections to detect cracks and corrosion in the actuator beam arm 
clevis must be performed on all affected airplanes, including those on 
which the rework or replacement has been accomplished. Paragraph B. of 
AD 91-05-16, which provided for optional terminating action for the 
repetitive inspections, has not been included in this AD.
    In addition, AD 91-05-16 requires a one-time inspection of the 
actuator beam attach bolts. However, there have been no known reports 
of bolt fractures since the effective date of AD 91-05-16. Therefore, 
the FAA has determined that further inspection of those bolts is 
unnecessary, and the corresponding requirement of AD 91-05-16 
(paragraph A.2.) has not been included in this AD. The inspection 
requirements of this AD are limited to the actuator beam arm clevis.
    Furthermore, the FAA finds it necessary to expand the applicability 
of this AD to include additional airplanes. The applicability of AD 91-
05-16 currently excludes in-production Model 737 series airplanes. 
However, the design change for incorporation on in-production airplanes 
can produce the same result as that of the preventive modification 
(rework) specified by Boeing Alert Service Bulletin 737-32A1224, 
Revision 1, dated April 12, 1990 which has been shown to be ineffective 
in preventing the unsafe condition. (That alert service bulletin is 
referenced as the appropriate source of service information in AD 91-
05-16 for accomplishment of the rework.) Therefore, the applicability 
of this AD includes all Model 737-100,-200, -300, -400, and -500 series 
airplanes.

Explanation of Relevant Service Information

    The FAA has reviewed and approved Boeing Service Bulletin 737-
32A1224, Revision 2, dated April 25, 1991. The content of Revision 2 is 
similar to that of Revision 1, which was cited as the appropriate 
source of service information for accomplishment of the requirements of 
AD 91-05-16. Revision 2 was issued to clarify the actions and to revise 
the effectivity for various actions.
    The FAA also has reviewed and approved Boeing Alert Service 
Bulletin 737-32A1314, dated April 15, 1999, which describes procedures 
for repetitive inspections of the clevis on certain actuator beam arm 
assemblies;

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the inspections include a visual inspection to detect corrosion and an 
ultrasonic inspection to detect cracking. The alert service bulletin 
also describes procedures for replacement of any beam arm having a 
cracked or corroded clevis with a new actuator beam arm.
    The note in Figure 1 of Boeing Alert Service Bulletin 737-32A1314 
references Temporary Revision (TR) 04-14 to the 737 Nondestructive Test 
(NDT) Manual. That note states that the TR would be issued prior to May 
14, 1999; in fact, the manufacturer released that TR by telegraphic 
release on April 26, 1999. The TR contains new information that is 
needed to perform ultrasonic inspections for airplanes having certain 
actuator beam arm assemblies. Specifically, the TR provides 
instructions for procuring or fabricating NDT transducers that are 
needed to accomplish the inspections for those certain airplanes.

Explanation of Requirements of Rule

    Since an unsafe condition has been identified that is likely to 
exist or develop on other airplanes of this same type design, this AD 
supersedes AD 91-05-16 to continue to require repetitive inspections to 
detect cracking of the actuator beam arm clevis of the MLG, and rework 
or replacement, if necessary. These actions are required to be 
accomplished in accordance with Boeing Alert Service Bulletin 737-
32A1224, Revision 1, or Boeing Service Bulletin 737-32A1224, Revision 
2.
    This AD adds repetitive detailed visual inspections to detect 
corrosion and repetitive ultrasonic inspections to detect cracking of 
the actuator beam arm clevis; these actions terminate the repetitive 
inspections described in Boeing Alert Service bulletin 737-32A1224, 
Revision 1, or Boeing Service Bulletin 737-32A1224, Revision 2. These 
inspections are required to be accomplished in accordance with Boeing 
Alert Service Bulletin 737-32A1314.
    For airplanes on which any corrosion or cracking is found during 
any of the newly added inspections, this AD requires replacement of the 
actuator beam arm with a new actuator beam arm in accordance with 
Boeing Alert Service Bulletin 737-32A1314.

Difference Between the Rule and the Relevant Service Information

    Operators should note that Alert Service Bulletin 737-32A1314 
specifies compliance in terms of either years or flight cycles. 
However, the threshold and repetitive interval required by paragraph 
(b) of this AD are specified in terms of calendar time only; i.e., 4 
years and 90 days, respectively. The unsafe condition identified by 
this AD is caused by corrosion, which is a function of time rather than 
accumulated flight cycles.

Interim Action

    This is considered to be interim action until final action is 
identified, at which time the FAA may consider further rulemaking.

Determination of Rule's Effective Date

    Since a situation exists that requires the immediate adoption of 
this regulation, it is found that notice and opportunity for prior 
public comment hereon are impracticable, and that good cause exists for 
making this amendment effective in less than 30 days.

Comments Invited

    Although this action is in the form of a final rule that involves 
requirements affecting flight safety and, thus, was not preceded by 
notice and an opportunity for public comment, comments are invited on 
this rule. Interested persons are invited to comment on this 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 under the caption 
ADDRESSES. All communications received on or before the closing date 
for comments will be considered, and this rule may be amended in light 
of the comments received. Factual information that supports the 
commenter's ideas and suggestions is extremely helpful in evaluating 
the effectiveness of the AD action and determining whether additional 
rulemaking action would be needed.
    Comments are specifically invited on the overall regulatory, 
economic, environmental, and energy aspects of the rule that might 
suggest a need to modify the 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 that 
summarizes each FAA-public contact concerned with the substance of this 
AD will be filed in the Rules Docket.
    Commenters wishing the FAA to acknowledge receipt of their comments 
submitted in response to this rule must submit a self-addressed, 
stamped postcard on which the following statement is made: ``Comments 
to Docket Number 99-NM-68AD.'' The postcard will be date stamped and 
returned to the commenter.

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.
    The FAA has determined that this regulation is an emergency 
regulation that must be issued immediately to correct an unsafe 
condition in aircraft, and that it is not a ``significant regulatory 
action'' under Executive Order 12866. It has been determined further 
that this action involves an emergency regulation under DOT Regulatory 
Policies and Procedures (44 FR 11034, February 26, 1979). If it is 
determined that this emergency regulation otherwise would be 
significant under DOT Regulatory Policies and Procedures, a final 
regulatory evaluation will be prepared and placed in the Rules Docket. 
A copy of it, if filed, 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 removing amendment 39-6913 (56 FR 
7561, February 25, 1991), and by adding a new airworthiness directive 
(AD), amendment 39-11165, to read as follows:

99-10-12 Boeing: Amendment 39-11165. Docket 99-NM-68-AD. Supersedes 
AD 91-05-16, Amendment 39-6913.

    Applicability: All Model 737-100, -200, -300, -400, and -500 
series airplanes; certificated in any category.

    Note 1: This AD applies to each airplane identified in the 
preceding applicability

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provision, regardless of whether it has been 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 detect and correct corrosion and cracking of the actuator 
beam arm of the main landing gear (MLG), which could result in 
damage to the control cables of the aileron and spoiler and 
consequent reduced controllability of the airplane, accomplish the 
following:

Restatement of the Requirements of AD 91-05-16, Amendment 39-6913

    (a) For airplanes listed in Boeing Alert Service Bulletin 737-
32A1224, Revision 1, dated April 12, 1990: Prior to the accumulation 
of 10,000 landings or 4 years of service, after new or overhauled 
MLG installation, whichever occurs first, or within the next 600 
landings after April 1, 1991 (the effective date of AD 91-05-16, 
amendment 39-6913), whichever occurs later, perform visual and 
ultrasonic inspections of the actuator beam arm clevis for evidence 
of cracking, in accordance with Boeing Alert Service Bulletin 737-
32A1224, Revision 1, dated April 12, 1990, or Revision 2, dated 
April 25, 1991.
    (1) If cracks are found, prior to further flight, remove and 
rework, or replace, the actuator beam arm in accordance with the 
service bulletin.
    (2) If no cracks are found, repeat the ultrasonic inspections in 
accordance with the service bulletin, at intervals not to exceed 600 
landings, until the initial inspection required by paragraph (b) of 
this AD has been accomplished.

New Requirements of this AD

    (b) Inspect the actuator beam arm clevis, by performing a 
detailed visual inspection to detect corrosion and an ultrasonic 
inspection to detect cracking, at the latest of the times specified 
in paragraphs (b)(1), (b)(2), (b)(3), and (b)(4) of this AD; in 
accordance with Boeing Alert Service Bulletin 737-32A1314, dated 
April 15, 1999. Accomplishment of these inspections constitutes 
terminating action for the requirements of paragraph (a) of this AD. 
Repeat the inspections specified by paragraph (b) of this AD 
thereafter at intervals not to exceed 90 days.
    (1) Inspect within 4 years since date of manufacture or 
installation of new landing gear.
    (2) Inspect within 4 years since the most recent landing gear 
overhaul.
    (3) Inspect within 4 years since accomplishment of the 
replacement of the actuator beam arm clevis performed in accordance 
with the alert service bulletin, or the rework performed in 
accordance with Boeing Alert Service Bulletin 737-32A1224, Revision 
1, dated April 12, 1990, or Boeing Service Bulletin 737-32A1224, 
Revision 2, dated April 25, 1991.
    (4) Inspect within 90 days after the effective date of this AD.

    Note 2: The Note in Figure 1 of Boeing Alert Service Bulletin 
737-32A1314 contains a reference to Temporary Revision (TR) 04-14 to 
the 737 Nondestructive Test Manual (NDT). The TR was issued April 
26, 1999, by telegraphic release. The TR provides instructions for 
procuring or fabricating NDT transducers needed to accomplish 
ultrasonic inspections on airplanes having certain actuator beam arm 
assemblies. Incorporation of the TR into the general revisions of 
the NDT is acceptable, provided that the information contained in 
the general revisions is identical to that specified in the TR.

Corrective Actions

    (c) If any corrosion or cracking is detected during any 
inspection required by paragraph (b) of this AD, prior to further 
flight, replace the actuator beam arm with a new actuator beam arm 
in accordance with Boeing Alert Service Bulletin 737-32A1314, dated 
April 15, 1999. Repeat the inspections required by paragraph (b) of 
this AD within 4 years after accomplishment of the replacement, and 
thereafter at intervals not to exceed 90 days.

Alternative Methods of Compliance

    (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). 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.

Special Flight Permits

    (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.

Incorporation by Reference

    (f) The actions shall be done in accordance with Boeing Alert 
Service Bulletin 737-32A1224, Revision 1, dated April 12, 1990; 
Boeing Service Bulletin 737-32A1224, Revision 2, dated April 25, 
1991; or Boeing Alert Service Bulletin 737-32A1314, dated April 15, 
1999; as applicable. 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 May 27, 1999.

    Issued in Renton, Washington, on May 4, 1999.
D.L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 99-11784 Filed 5-11-99; 8:45 am]
BILLING CODE 4910-13-U