[Federal Register Volume 64, Number 88 (Friday, May 7, 1999)]
[Rules and Regulations]
[Pages 24505-24507]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 99-11468]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 97-NM-53-AD; Amendment 39-11161; AD 99-10-08]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 767 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 767 series airplanes, that requires 
a detailed visual inspection to detect corrosion inside the forward 
trunnion joint of the main landing gear (MLG); follow-on actions; and 
repair, if necessary. This amendment also provides for optional 
terminating action for the repetitive inspections. This amendment is 
prompted by reports of corrosion at the forward trunnion thrust face, 
tabs, and the internal threads of the forward trunnion of the MLG due 
to moisture in the forward trunnion joint. The actions specified by 
this AD are intended to prevent corrosion of the forward trunnion 
joint, which could lead to a stress corrosion fracture of the forward 
trunnion and possible consequent collapse of the MLG.

DATES: Effective June 11, 1999.
    The incorporation by reference of certain publications listed in 
the regulations is approved by the Director of the Federal Register as 
of June 11, 1999.

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: James G. Rehrl, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 
1601 Lind Avenue, SW., Renton, Washington; telephone (425) 227-2783; 
fax (425) 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 767 series 
airplanes was published in the Federal Register on August 5, 1998 (63 
FR 41739). That action proposed to require a detailed visual inspection 
to detect corrosion inside the forward trunnion joint of the main 
landing gear (MLG); follow-on actions; and repair, if necessary. That 
action also proposed to provide for optional terminating action for the 
repetitive inspections.
    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

    Two commenters support the proposal.

Request to Clarify Certain Requirements

    One commenter, the manufacturer, requests that paragraph (b) of the 
proposal be revised to clarify that the addition of corrosion-
inhibiting compound to the trunnion joint is also needed to terminate 
the proposed inspections.
    The FAA concurs. Although the appropriate service information for 
this AD provides procedures to apply corrosion-inhibiting compound to 
the trunnion joint whenever the chrome plate is applied to the 
trunnion, this was not explicitly stated in the wording of the AD. 
Therefore, the FAA has revised paragraphs (a)(1), (a)(2), and (b) of 
the final rule (where discussion of terminating actions occurs) to 
clarify that the terminating action will consist of applying chrome 
plate to the trunnion tabs and applying corrosion-inhibiting compound 
to the trunnion joint.

Request to Withdraw the NPRM or Require the Latest Modification

    One commenter requests that the FAA withdraw the proposal, or at 
least revise the requirements to mandate the latest modification as the 
terminating action. The commenter states that the terminating action 
specified in the proposed rule will not prevent corrosion. The 
commenter states that its own inspections of other trunnions on which 
the terminating modification has been accomplished indicate that the 
terminating modification is inadequate to prevent corrosion. The 
commenter further notes that the proposed modification (which consists 
of applying chrome plate) does not address the areas of the joint that 
have proved to be the most susceptible to corrosion, e.g., the threads 
on the internal diameter of the trunnion and the aft surface of the 
joint. The commenter concludes that, in light of the fact that Boeing 
has recently abandoned its design philosophy for this joint, the 
proposed terminating modification is ``dated.'' Specifically, the 
commenter notes that the latest Boeing design entails removing the 
threads of the joint altogether. Further, the commenter states that 
mandating the proposal would impose costly and disruptive maintenance 
requirements if the proposal requires incorporating an ineffective 
modification when better solutions exist.
    The FAA does not concur with the commenter's request to withdraw 
the proposal or to revise the terminating action specified in the AD. 
The FAA considers that, in this case, there are three factors that make 
stress corrosion cracking of the forward trunnion a safety concern. 
First, the material (i.e., 4340M high strength steel) is known to be 
highly susceptible to stress corrosion cracking; second, the material 
is in an environment that allows corrosion to form (as has been 
demonstrated numerous times); and third, the material is at times 
exposed to sustained tensile stresses. Since an unsafe condition has 
been identified, the FAA considers it appropriate and necessary to 
issue the final rule. Although the commenter's position is that the 
terminating modification is inadequate in preventing corrosion, the FAA 
has received no reports of corroded trunnions being identified after 
the terminating modification has been accomplished. The FAA has 
determined that since the release of Boeing Alert Service Bulletin 767-
32A0127, dated January 29, 1996 (the appropriate service information 
for this final rule), an insufficient amount of time has passed that 
would allow corrosion to re-

[[Page 24506]]

initiate on a MLG forward trunnion that has been removed from an 
airplane, then disassembled, inspected, cleaned, chrome-plated, and re-
installed with corrosion inhibiting compound. Therefore, no change is 
necessary to this final rule in that regard.
    The FAA acknowledges that the internal diameter of the trunnion and 
the aft surface of the joint are susceptible to corrosion, and that the 
modification specified in this final rule does not specifically address 
applying chrome plating to those areas. However, the FAA has determined 
that the required inspections for corrosion and the modification 
specified by this final rule are adequate to detect or prevent 
corrosion of the forward trunnion joint. If information becomes 
available that indicates that the terminating action may be inadequate, 
the FAA may initiate further rulemaking.
    The commenter also asserts that the proposal would impose costly 
and disruptive maintenance requirements if it requires incorporating an 
ineffective modification when better solutions already exist. As 
explained previously, the FAA has received no information indicating 
that the modification is ineffective. Additionally, the FAA is aware 
that Boeing has developed a new design for the forward trunnion joint, 
which entails, among other things, the removal of the internal threads. 
The FAA also notes that the service information relating to the new 
design is not available for FAA review and approval at the current 
time. However, under the provisions of paragraph (c) of the final rule, 
the FAA will consider requests for approval of an alternative method of 
compliance if sufficient data are submitted to substantiate that such a 
design change would provide an acceptable level of safety.

Request to Withdraw the Proposal or Add Further Requirements

    This same commenter requests that if the proposal is not withdrawn, 
it should simply require operators to remove and report any corrosion 
at overhaul (not to exceed 10 years), with aggressive lubrication 
intervals of 250 flight cycles or less. The FAA infers that the 
commenter is basing its request on a statement (of the commenter's) 
that contends that the stress levels in the forward trunnion area are 
below the stress corrosion cracking threshold for crack formation. 
Therefore, the commenter concludes that no risk exists for stress 
corrosion cracking to start.
    The FAA does not concur with the commenter's request to withdraw 
the NPRM. For reasons specified in the discussion of the previous 
comment, the FAA finds that this rule is appropriate and necessary. 
Further, the FAA does not concur with the request to require removal of 
corrosion during overhaul. The FAA finds that the concept of stress 
corrosion threshold is not applicable to this situation because the 
affected structure is already corroded. The use of a stress corrosion 
threshold is only applicable during the material selection phase of a 
new design; it is not useful for predicting the behavior of corroded 
structure. Therefore, the FAA has determined that no change to the 
final rule is necessary.

Request to Revise the Compliance Time

    One commenter states that the 18-month initial compliance time is 
too aggressive and will cause unnecessary costs and scheduling 
problems.
    The FAA infers that the commenter would like the compliance time to 
be extended to correlate with the airplane's next scheduled overhaul. 
The FAA does not concur that the compliance time should be revised. In 
developing an appropriate compliance time, the FAA considered the 
safety implications, and normal maintenance schedules for timely 
accomplishment of the inspection and follow-on actions. In 
consideration of these items, as well as the reports of corrosion at 
the forward trunnion thrust face, tabs, and internal threads of the 
forward trunnion of the MLG, the FAA finds that a period of 18 months 
represents an appropriate compliance threshold wherein the inspection 
and follow-on actions can be accomplished during scheduled maintenance 
for the majority of affected operators and an acceptable level of 
safety can be maintained. However, under the provisions of paragraph 
(c) of the final rule, the FAA may approve requests for adjustments to 
the compliance time if data are submitted to substantiate that such 
adjustments would provide an acceptable level of safety.

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 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.

Cost Impact

    There are approximately 455 Boeing Model 767 series airplanes of 
the affected design in the worldwide fleet. The FAA estimates that 151 
airplanes of U.S. registry will be affected by this AD.
    It will take approximately 8 work hours per airplane to accomplish 
the visual inspection, at an average labor rate of $60 per work hour. 
Based on these figures, the cost impact of the required inspection on 
U.S. operators is estimated to be $72,480, or $480 per airplane, per 
inspection cycle.
    The cost impact figures above do not account for the time to gain 
access to the forward trunnion joint or to return a main landing gear 
to service. In this case, however, the access and close-up work hours 
may account for the predominant portion of the total cost impact of 
this AD. It is estimated that it will take approximately 65 work hours 
to gain access to both forward trunnion joints, and 89 work hours to 
return the airplane to service. If these costs are included, the cost 
impact for the required inspections will be approximately $1,467,720, 
or $9,720 per airplane, per inspection cycle.
    Repair of the forward trunnions (two per airplane), if accomplished 
(which may include both corrosion blend-out repairs as well as the 
application of chrome plate to certain portions of the forward 
trunnion), will take approximately 72 work hours to accomplish, at an 
average labor rate of $60 per work hour. The cost of the repair kits 
will be approximately $16,000 per airplane. Based on these figures, the 
cost impact of the repair on U.S. operators is estimated to be 
$3,068,320, or $20,320 per airplane.
    The cost impact figures discussed above are 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

[[Page 24507]]

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:

99-10-08  Boeing: Amendment 39-11161. Docket 97-NM-53-AD.

    Applicability: Model 767 series airplanes, manufacturer's line 
positions 001 through 455 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 
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 (c) 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 corrosion of the forward trunnion joint of the main 
landing gear (MLG), which could lead to a stress corrosion fracture 
of the forward trunnion and possible consequent collapse of the MLG, 
accomplish the following:
    (a) Within 6 years since the outer cylinder of the MLG was new, 
last overhauled, or installed (replaced) after the last corrosion 
repair in accordance with Boeing Alert Service Bulletin 767-32A0127, 
dated January 29, 1996; or within 18 months after the effective date 
of this AD; whichever occurs later: Perform a detailed visual 
inspection to detect corrosion inside the forward trunnion joint and 
the internal threads of the MLG; in accordance with the 
Accomplishment Instructions of Boeing Alert Service Bulletin 767-
32A0127, dated January 29, 1996.
    (1) If no corrosion of the forward trunnion joint is found, 
prior to further flight, accomplish either paragraph (a)(1)(i) or 
(a)(1)(ii) of this AD.
    (i) Apply chrome plating to the forward trunnion thrust and tab 
faces and apply corrosion-inhibiting compound to the trunnion joint 
in accordance with the alert service bulletin. Accomplishment of 
this application of chrome plating constitutes terminating action 
for the requirements of this AD.
    (ii) Apply corrosion-inhibiting compound to the forward trunnion 
joint in accordance with the Accomplishment Instructions of the 
alert service bulletin. Repeat the detailed visual inspection 
thereafter at intervals not to exceed six years or until chrome 
plating is applied to the forward trunnion thrust and tab faces and 
corrosion-inhibiting compound is applied to the trunnion joint, in 
accordance with the alert service bulletin.
    (2) If any corrosion of the forward trunnion joint is found, 
prior to further flight, accomplish either paragraph (a)(2)(i) or 
(a)(2)(ii) of this AD.
    (i) Repair the forward trunnion, apply chrome plating to the 
forward trunnion thrust and tab faces, and apply corrosion-
inhibiting compound; in accordance with the alert service bulletin. 
Accomplishment of this application of chrome plating and corrosion-
inhibiting compound constitutes terminating action for the 
requirements of this AD.
    (ii) Repair the forward trunnion and apply corrosion-inhibiting 
compound to the forward trunnion joint in accordance with the alert 
service bulletin. Repeat the detailed visual inspection thereafter 
at intervals not to exceed six years or until chrome plating is 
applied to the forward trunnion thrust and tab faces in accordance 
with the alert service bulletin.
    (b) Replacement, repair, or overhaul of the outer cylinder of 
the MLG that includes the application of chrome plating to the 
forward trunnion thrust and tab faces and application of corrosion-
inhibiting compound, in accordance with Boeing Alert Service 
Bulletin 767-32A0127, dated January 29, 1996, constitutes 
terminating action for the requirements of this AD.

Alternative Methods of Compliance

    (c) 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.

Special Flight Permits

    (d) Special flight permits may be issued in accordance with 
Secs. 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

    (e) The actions shall be done in accordance with Boeing Alert 
Service Bulletin 767-32A0127, dated January 29, 1996. 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.
    (f) This amendment becomes effective on June 11, 1999.

    Issued in Renton, Washington, on April 30, 1999.
D. L. Riggin,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 99-11468 Filed 5-6-99; 8:45 am]
BILLING CODE 4910-13-U