Airworthiness Directives; Boeing Model 767 Series Airplanes

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]

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