Airworthiness Directives; Boeing Model 767 Series Airplanes

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 97-NM-186-AD]

RIN 2120-AA64

Airworthiness Directives; Boeing Model 767 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Supplemental notice of proposed rulemaking; reopening of

comment period.

-----------------------------------------------------------------------

SUMMARY: This document revises an earlier proposed airworthiness

directive (AD), applicable to certain Boeing Model 767 series

airplanes, that would have required repetitive inspections to ensure

the proper condition of the engine thrust link components, and follow-

on corrective action, if necessary; and replacement of the end cap

assembly with an improved assembly. Such replacement, when

accomplished, would terminate the repetitive inspections. That proposal

was prompted by a report of fatigue cracking of end cap bolts caused by

improper installation. This new action revises the proposed rule by

adding a repair requirement and by clarifying the type of inspection

and terminology used in describing the parts to be inspected. The

actions specified by this new AD are intended to prevent failure of the

end cap assembly, which could lead to separation of the engine from the

airplane in the event of a primary thrust linkage failure.

DATES: Comments must be received by November 10, 1999.

ADDRESSES: Submit comments in triplicate to the Federal Aviation

Administration (FAA), Transport Airplane Directorate, ANM-114,

Attention: Rules Docket No. 97-NM-186-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. This information may be examined at the FAA, Transport

Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington.

FOR FURTHER INFORMATION CONTACT: James G. Rehrl, Aerospace Engineer,

Airframe Branch, ANM-120S, FAA, Transport Airplane Directorate, Seattle

Aircraft Certification Office, 1601 Lind Avenue, SW., Renton,

Washington 98055-4056; telephone (425) 227-2783; fax (425) 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 97-NM-186-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-114, Attention: Rules

Docket No. 97-NM-186-AD, 1601 Lind Avenue, SW., Renton, Washington

98055-4056.

Discussion

A proposal to amend part 39 of the Federal Aviation Regulations (14

CFR part 39) to add an airworthiness directive (AD), applicable to

certain Boeing Model 767 series airplanes, was published as a notice of

proposed rulemaking (NPRM) in the Federal Register on May 20, 1998 (63

FR 27696). That NPRM would have required repetitive inspections to

detect improper installation or fatigue damage of the end cap of the

forward engine mount, and replacement of the end cap assembly with an

improved assembly. Such replacement, when accomplished, would terminate

the repetitive inspections. That NPRM was prompted by a report of

fatigue cracking of end cap bolts caused by improper installation. That

condition, if not corrected, could result in failure of the end cap

assembly, which could lead to separation of the engine from the

airplane in the event of a primary thrust linkage failure.

Comments

Due consideration has been given to the comments received in

response to the NPRM:

One commenter states that it is not affected by the proposal

because its Model 767-200ER series airplanes are powered by General

Electric engines. Another commenter generally supports the proposal.

Request To Withdraw the Original NPRM

One commenter does not consider that issuance of the original NPRM

is necessary for the following reasons:

1. The commenter states that ``regulatory action mandating

incorporation of Boeing Alert Service Bulletin 767-71A0087 is

unwarranted for JT9D powered Model 767 aircraft'' for several reasons.

First, the original

[[Page 56710]]

NPRM was issued solely because the part numbers of the end caps and

bolts on Model 767 and Model 747-400 series airplanes are the same.

Second, the alert service bulletin was issued on the basis of one

report of broken end cap bolts by one operator of a Model 747-400

series airplane.

The FAA does not concur that the original NPRM should be withdrawn.

Issuance of the original NPRM was not based on the fact that both end

caps have the same part number, but on the fact that the configuration

of the end cap assembly is identical. The configuration of the end cap

assembly for Model 767 and 747 series airplanes is identical in all

relevant respects. Therefore, if an end cap assembly is installed

incorrectly in either of those airplane models, the same unsafe

condition is likely to occur. In addition, the unsafe condition is

likely to occur regardless of whether the airplane is powered by Pratt

& Whitney Model JT9D or Model PW4000 series engines, as the

installations of those airplane engines also are identical. In light of

this, the FAA has determined that an unsafe condition exists. No change

to the supplemental NPRM is necessary in this regard.

2. The commenter states that the cause of the bolt failure on a

Model 747-400 series airplane was attributed to a personnel error when

the end cap was installed backwards. The commenter adds that one

isolated incident involving a personnel error ``does not warrant

drastic repetitive inspections.''

The FAA does not concur that the original NPRM should be withdrawn.

While personnel error was involved in the mis-installation of the end

cap, it is the ease by which an end cap can be installed backwards that

makes it likely that this condition could exist on other airplanes. For

this reason, the FAA considers that an unsafe condition is likely to

develop on other airplane models of the same design, and that issuance

of this AD and the repetitive inspections required by this AD are

necessary to ensure continued operational safety. No change to the

supplemental NPRM is necessary in this regard.

3. The commenter states that the end cap and bolts are routinely

inspected for defects when they are removed from the assembly. In

addition, in the entire operating history of Model 767 series airplanes

powered by Pratt & Whitney Model JT9D series engines, there is no

documented event of any operator experiencing failure of an end cap or

bolt. Further, there is no evidence that the end caps were ever

installed backwards on any Model 767 series airplane.

The FAA does not concur that the original NPRM should be withdrawn.

Even though the operator may conduct a routine inspection of the end

cap and bolts for defects, additional inspections are required because

of the possibility of early fatigue failure. The FAA considers this AD

necessary in order to address two major concerns:

First, if an end cap were installed incorrectly, it would

automatically pick up thrust loads on every flight and result in an

early fatigue failure of the end cap assembly. Thus, if the primary

load path provided by the thrust links, evener bar, and engine lugs

were to then experience a failure, the engine would separate from the

airplane almost immediately.

Second, investigation has revealed that even a properly

installed end cap assembly has an inadequate fatigue life. Analysis and

testing indicate that if the primary load path fails, the end cap

assembly then would react all of the new loads and cause the end cap

assembly to fail within a relatively small number of flight cycles.

Such failure would occur even if the end cap assembly had been entirely

intact at the time the primary load path failed. For this reason, the

original NPRM specifies repetitive inspections of the primary load path

(i.e., the thrust link, evener bar, and engine lugs) until

accomplishment of the replacement action specified in Work Packages 3

or 4.

The FAA considers that the lack of defects found in the operator's

end caps implies merely that the original end caps were installed

correctly, as a properly installed end cap would not react any loads

during normal flight operations, thereby making it unlikely that any

fatigue damage would have occurred. However, because it has been

determined that the existing end cap assembly has an inadequate fatigue

life, the FAA considers that the requirements of this AD are necessary

to ensure the operational safety of the fleet. No change to the

supplemental NPRM is necessary in this regard.

4. The commenter states that the alert service bulletin mandates a

visual check and an ultrasonic on-wing [non-destructive test (NDT)]

inspection of the evener bar and thrust links for the engine mounts for

Pratt & Whitney Model JT9D series engines, but no on-wing ultrasonic

inspection is specified for Model PW4000 series engines. If repetitive

on-wing ultrasonic inspections are waived for the higher thrust Model

PW4000 series engines, there is no justification to require those

inspections for the lower thrust Model JT9D series engines. Further,

the operating history of airplanes powered by Model JT9D series engines

does not support any regulatory action regarding the forward lower

engine mount.

The FAA does not concur that the original NPRM should be withdrawn.

The FAA points out that the original NPRM makes it clear in the

``Differences'' paragraph that the two airplane groups for Model 767

series airplanes, Group 1 airplanes (with JT9D engines) and Group 2

airplanes (with PW4000 engines), are to be treated exactly the same.

According to the manufacturer's fleet utilization data base, there

should never be a case of any Group 2 airplane ever reaching the

threshold of 16,000 flight cycles before it reaches the 3-year

compliance time for the mandatory terminating action. Although the

logic diagram in Figure 1 of the alert service bulletin specifies that

operators of Group 2 airplanes (i.e., airplanes with Model PW4000

series engines) [with more than 16,000 flight cycles] should contact

the manufacturer, the FAA considers that this instruction was included

on the off-chance that an airplane might fall into this category.

However, this does not imply that any such airplanes would be waived

from the NDT inspection requirements. On the contrary, such airplanes

would be handled on a case-by-case basis, with every expectation that

NDT inspections would be required at shorter inspection intervals

because of the higher fatigue damage that could be caused by the higher

thrust Model PW4000 series engines. No change to the supplemental NPRM

is necessary.

Request To Clarify Inspection Requirements and Components To Be

Inspected

One commenter, the manufacturer, requests certain changes to the

``Explanation of Relevant Service Information'' paragraph in the

original NPRM. The commenter contends that the AD should refer to

inspections of the ``engine thrust link components'' rather than to

inspections of the ``end cap.''

The FAA concurs that the commenter's suggested changes add clarity

and technical accuracy to the supplemental NPRM. Additionally, Boeing

Alert Service Bulletin 767-71A0087, dated October 10, 1996, does not

specify inspections of the ``end cap,'' but only includes inspections

of the ``forward engine mount'' to ensure that the thrust links, evener

bar, associated engine lugs, and attaching hardware are firmly

attached. Although the ``Explanation of Relevant Service Information''

paragraph is not included

[[Page 56711]]

in this supplemental NPRM, the FAA has determined that certain changes

are necessary in this AD for several reasons.

The FAA considers that requiring operators ``to ensure the proper

condition of the engine thrust link components'' more accurately

describes the action required for the inspection rather than ``to

detect improper installation or fatigue damage of the end cap of the

forward engine mount.'' The FAA points out that ``fatigue damage of the

end cap of the forward engine mount,'' which involves the secondary

load path, could not be detected until the forward engine mount was

disassembled. In addition, the inspections specified by the alert

service bulletin are for ``engine thrust link components,'' not the

``end cap'' itself.

This supplemental NPRM correlates the corrective action to the

presence or absence of damage to the engine thrust link components. In

addition, the engine thrust link components, which involve the primary

load path, can be inspected with no disassembly of the forward engine

mount. In light of this information, the FAA has made the appropriate

changes to the ``Summary'' paragraph of this supplemental NPRM.

Request To Include Repair of Discrepancies

One commenter, the manufacturer, requests that paragraph (d) of the

original NPRM be revised to require that all discrepancies or damage

found be repaired in accordance with an approved FAA procedure.

The FAA concurs partially. The action required by paragraph (d) of

the original NPRM is now included in paragraphs (c), (c)(1), and (c)(2)

of the supplemental NPRM. The repair requirement is added in paragraph

(c)(1), and the action for accomplishment of Work Package 3 is included

in paragraph (c)(2). Because the repair procedures are not specified in

Work Package 3 of the alert service bulletin, it is necessary for this

supplemental NPRM to require that any repairs be accomplished in

accordance with a method approved by the Manager, Seattle Aircraft

Certification Office (ACO).

Explanation of Changes Made to the Supplemental NPRM

The FAA has clarified one of the inspection requirements contained

in the original NPRM. Whereas the original NPRM specified the

accomplishment of Work Package 1 (visual inspection of the forward

engine mount), the FAA has revised this supplemental NPRM to clarify

that its intent is to require a detailed visual inspection.

Additionally, a note has been added to the supplemental NPRM to define

that inspection.

The FAA has deleted the reference to paragraph (c) that was

included in paragraph (a) of the original NPRM, which stated that

``Where Boeing Alert Service Bulletin 767-71A0087, dated October 10,

1996, specifies that the actions required by this AD may be

accomplished in accordance with an operator's equivalent procedure,'

the actions must be accomplished in accordance with Chapter 71-00-00 of

the Boeing 767 Airplane Maintenance Manual (AMM), as specified in the

alert service bulletin.'' The FAA has determined that the required

inspections and replacement actions specified in paragraphs (a), (b),

and (c)(2) of the supplemental NPRM are adequately addressed in the

alert service bulletin. Therefore, reference to a specific chapter of

the AMM is not necessary.

Paragraphs (a)(1) and (a)(2) of this supplemental NPRM have been

revised to clarify the inspection requirements.

Explanation of Changes Made to This Final Rule

The FAA has clarified the inspection requirement contained in the

proposed AD. Whereas the proposal specified a visual inspection, the

FAA has revised this final rule to clarify that its intent is to

require a detailed visual inspection. Additionally, a note has been

added to the final rule to define that inspection.

Conclusion

Since these changes expand the scope of the originally proposed

rule, the FAA has determined that it is necessary to reopen the comment

period to provide additional opportunity for public comment.

Cost Impact

There are approximately 239 Model 767 series airplanes of the

affected design in the worldwide fleet. The FAA estimates that 96

airplanes of U.S. registry will be affected by this AD, that it will

take approximately 37 work hours per airplane (18.5 work hours per

engine) to accomplish the required inspections, and that the average

labor rate is $60 per work hour. Based on these figures, the cost

impact of the AD on U.S. operators is estimated to be $213,120, or

$2,220 per airplane, per inspection cycle.

It will take approximately 135 work hours per airplane (67.5 work

hours per engine) to accomplish the required replacement of the forward

engine mount end cap and bolts, and the average labor rate is $60 per

work hour. Required parts would cost approximately $1,000 per airplane.

Based on these figures, the cost impact of the AD on U.S. operators is

estimated to be $873,600, or $9,100 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 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 97-NM-186-AD.

[[Page 56712]]

Applicability: Model 767 series airplanes, powered by Pratt &

Whitney Model JT9D or Model PW4000 series engines, as listed in

Boeing Alert Service Bulletin 767-71A0087, dated October 10, 1996;

certificated in any category.

Note: 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 (e) 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 separation of the engine from the airplane

in the event of a primary thrust linkage failure, accomplish the

following:

Initial and Repetitive Inspections

(a) For Groups 1 and 2 airplanes: Accomplish paragraphs (a)(1),

(a)(2), and (a)(3) of this AD, as applicable, in accordance with

Boeing Alert Service Bulletin 767-71A0087, dated October 10, 1996.

(1) Within 500 flight hours or 300 flight cycles after the

effective date of this AD, whichever occurs later: Accomplish Work

Package 1 (a detailed visual inspection of the forward engine mount

to ensure that the thrust link, evener bar, associated lugs, and

attaching hardware are firmly attached). Thereafter, repeat Work

Package 1 at the intervals specified in the alert service bulletin

until the requirements of either paragraph (a)(2) or (a)(3) of this

AD are accomplished.

Note 2: For the purposes of this AD, a detailed visual

inspection is defined as: ``An intensive visual examination of a

specific structural area, system, installation, or assembly to

detect damage, failure, or irregularity. Available lighting is

normally supplemented with a direct source of good lighting at an

intensity deemed appropriate by the inspector. Inspection aids such

as mirrors, magnifying lenses, etc. may be used. Surface cleaning

and elaborate access procedures may be required.''

(2) Prior to the accumulation of 16,000 total flight cycles on

any engine or within 500 flight hours or 300 flight cycles after the

effective date of this AD, whichever occurs latest: Accomplish Work

Package 2 (non-destructive test inspection of the forward engine

mount to ensure the proper condition of the engine thrust link

components). Thereafter, repeat Work Package 2 on that engine at the

intervals specified in the alert service bulletin until the

requirements of paragraph (a)(3) of this AD are accomplished.

Accomplishment of Work Package 2 constitutes terminating action for

the repetitive inspections required by paragraph (a)(1) of this AD

for that engine.

Replacement and Terminating Action

(3) Within 3 years after the effective date of this AD:

Accomplish Work Package 3 (end cap and bolt replacement of the

forward engine mount). Accomplishment of Work Package 3 constitutes

terminating action for the requirements of this AD for Groups 1 and

2 airplanes.

(b) For Group 3 airplanes: Within 3 years after the effective

date of this AD, accomplish Work Package 4 (bolt replacement) in

accordance with Boeing Alert Service Bulletin 767-71A0087, dated

October 10, 1996.

Repair and Replacement Action

(c) For all airplanes: If any discrepancy (including an

improperly installed or damaged engine thrust link component) is

found during any inspection required by this AD, prior to further

flight, accomplish the actions required by paragraphs (c)(1) and

(c)(2) of this AD.

(1) Repair any discrepancies in accordance with a method

approved by the Manager, Seattle Aircraft Certification Office

(ACO), FAA, Transport Airplane Directorate. For a repair method to

be approved by the Manager, Seattle ACO, as required by this

paragraph, the Manager's approval letter must specifically reference

this AD.

(2) Accomplish Work Package 3 in accordance with Boeing Alert

Service Bulletin 767-71A0087, dated October 10, 1996.

Spares

(d) As of the effective date of this AD, no person shall install

a forward engine mount end cap having part number 310T3026-1 on any

airplane.

Alternative Method of Compliance

(e) 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 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 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

(f) 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.

Issued in Renton, Washington, on October 15, 1999.

D.L. Riggin,

Acting Manager, Transport Airplane Directorate, Aircraft Certification

Service.

[FR Doc. 99-27564 Filed 10-20-99; 8:45 am]

BILLING CODE 4910-13-p