[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
