Airworthiness Directives; Boeing Model 767 Series Airplanes Equipped With Carbon Brakes

DEPARTMENT OF TRANSPORTATION

14 CFR Part 39

[Docket No. 93-NM-218-AD; Amendment 39-8995; AD 94-16-05]

Airworthiness Directives; Boeing Model 767 Series Airplanes

Equipped With Carbon Brakes

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

repetitive inspections to detect cracking, corrosion, and wear of

various components of the main landing gear (MLG) brake assembly, and

correction of discrepancies. This amendment is prompted by reports

indicating that components in the MLG assembly have been damaged due to

the consequences of vibration in the brake assembly. The actions

specified by this AD are intended to minimize the exposure of the brake

assembly to the consequences of a vibratory condition that could

ultimately lead to failure of components of the MLG; such failure could

severely affect the braking capability of the airplane while on the

ground.

DATES: Effective September 14, 1994.

The incorporation by reference of certain publications listed in

the regulations is approved by the Director of the Federal Register as

of September 14, 1994.

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: Kristin Larson, Aerospace Engineer,

Systems & Equipment Branch, ANM-130S, FAA, Transport Airplane

Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue,

SW., Renton, Washington 98055-4056; telephone (206) 227-1760; fax (206)

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 March 15, 1994 (59

FR 11946). That action proposed to require inspections to detect

cracking, corrosion, and wear of various components of the main landing

gear (MLG) brake assembly, and correction of discrepancies.

Interested persons have been afforded an opportunity to participate

in the making of this amendment. Due consideration has been given to

the comments received.

One commenter supports the proposal.

Several commenters request that the proposal be withdrawn. These

commenters contend that AD 94-03-07, amendment 39-8814 (59 FR 7897,

February 17, 1994), adequately addresses the safety concerns related to

failures caused by the vibration phenomenon of the brakes. That AD is

applicable to the same airplanes that would be affected by the

proposal, and requires that operators incorporate modifications and

perform several different types of inspections to detect cracking and

other damage of various components of the MLG brake assembly.

Additionally, one commenter advises that every operating airplane

affected by AD 94-03-07 is currently in compliance with that AD and,

due to the efforts of the operators of these airplanes, there has been

a ``dramatic effect'' in addressing the known brake failure modes.

The FAA does not concur with the request to withdraw the AD. The

issuance of AD 94-03-07 was prompted by incidents of brake failure and

by physical evidence, which indicated that certain components in the

brake load path are subject to damage or failure due to the vibration

phenomenon of the brakes. Such damage or failures can contribute to the

overall failure of the braking system. While accomplishment of the

requirements of AD 94-03-07 will minimize the likelihood or effect of

failures of certain components within the brake system, accomplishment

of the repetitive inspection requirements of this new AD will address

potential damage that could further aggravate the identified vibration

phenomenon. While there have been no in-service incidents of failure of

certain of these specific components, the FAA has determined that the

potential exists for such failures to occur, due to the configuration

of the MLG brake assembly and the continuing occurrences of the

vibration phenomenon of the brakes. If the failure of the subject

components were to occur, it could further aggravate the vibratory

condition and weaken the brake load path, possibly leading to further

failures or loss of braking. No evidence has been submitted to the FAA

to indicate that this potential for failure does not exist, or to

justify that inspection of these components is not necessary. In light

of these factors, the FAA has determined that this final rule is both

appropriate and warranted.

One commenter states that the proposed inspections to detect

corrosion and damage to the brake hardware are currently part of

operators' maintenance programs. Prudent operators would be expected to

adjust their maintenance programs to reflect the changes in the

inspections and inspection intervals recommended by Boeing Service

Bulletin 767-32-0128 (which is referenced in the proposal). The

commenter contends that the incidents upon which the proposed AD and AD

94-03-07 are based are the result of design defects rather than

improper maintenance; therefore, an operator's maintenance program

should not have to be revised via an AD in order to address the safety

concern. The commenter suggests that the FAA should not require the

operator's maintenance program to be revised unless it can show that

the maintenance program is inadequate. In this regard, the commenter

requests that the FAA review its justification for the proposed rule to

ensure that it is sufficient to satisfy the requirements of part 39 of

the Federal Aviation Regulations (FAR) (14 CFR part 39),

``Airworthiness Directives.''

The FAA concurs with the commenter's observation that the unsafe

condition addressed by this AD action is the result of a design

deficiency and not a maintenance deficiency; however, the FAA does not

concur with the commenter's inference that this AD is not justified.

This commenter appears to be confusing the basis for finding of an

unsafe condition with the appropriate means of addressing the unsafe

condition. While it is true that the unsafe condition is based on a

design deficiency of the MLG assembly, there currently is no permanent

``design fix'' to eliminate the problem. Therefore, although a design

fix would be the ultimate intention, the FAA has determined that the

accomplishment of the inspection requirements of this AD, in the

interim, is necessary in order to minimize the occurrence of brake

failures due to the brake vibration phenomenon and to ensure that an

acceptable level of safety is maintained. With regard to the

commenter's statement concerning maintenance programs, even though a

parallel inspection action currently may be part of an operator's

maintenance program, this AD serves as the means available to the FAA

for mandating the appropriate inspection actions and ensuring their

accomplishment at timely intervals by all affected operators.

Further, according to part 39 of the FAR, the issuance of an AD

must be based on the finding that an unsafe condition exists or is

likely to develop in aircraft of a particular type design. This AD is

prompted by what the FAA has determined to be an unsafe condition to

which Model 767 series airplanes equipped with carbon brakes are

subject. That unsafe condition entails the failure of MLG components

and the subsequent loss of braking capability, which is brought about

by the effects of a vibration phenomenon that is known to exist in the

brake assembly of these airplanes. The FAA also has determined that

repetitive inspections of the affected area must be mandated in order

to minimize the failure of the components and to ensure that safety is

not degraded. The appropriate vehicle for mandating such action to

correct an unsafe condition is the airworthiness directive.

Accordingly, the issuance of this AD is justified under part 39 of the

FAR.

One commenter requests an explanation of why the requirements of AD

94-03-07 are considered interim action. The FAA responds by noting that

it considers the requirements of both AD 94-03-07 as well as this new

AD to be interim action. The accomplishment of the requirements of

these AD's is intended to minimize the occurrence of brake failures due

to the brake vibration phenomenon. These actions do not eliminate the

vibration phenomenon itself, however, as has been verified by a recent

incident that occurred in March 1994. During that incident, an airplane

that was in compliance with AD 94-03-07 experienced a rejected takeoff

in which there was no detected brake loss, but brake components were

found to be fractured or damaged during an inspection performed after

the incident occurred. The damage that was sustained as a result of

that incident was primarily in components other than those addressed by

AD 94-03-07. It is apparent that failure of the brake components due to

vibration can still occur. The FAA maintains that design changes are

needed that will eliminate or significantly reduce the vibration

phenomenon recognized in the Model 767 carbon brake system, or

significantly reduce the occurrence of failures in the brake load path.

The FAA considers that the actions required by AD 94-03-07 and by this

new AD are interim actions until such design changes are developed and

available.

Several commenters request that the proposed compliance terms be

revised from ``hours time-in-service'' to ``flight cycles.'' These

commenters point out that the procedures specified in the referenced

Boeing service bulletin are in terms of flight cycles, not hours. The

FAA concurs. The reference to ``hours time-in-service'' that appeared

in the proposal was an error. The wording of the final rule has been

corrected to specify ``flight cycles''. This correction will not impose

any additional burden on affected operators; it will relieve operators

from having to perform the inspections earlier or more often than is

actually necessary.

These same commenters request that the compliance time for the

inspections that would be required by paragraph (a) be revised from the

proposed 1,500 hours time-in-service to 1,600 flight cycles. The

commenters state that AD 94-03-07 requires that the rod linkage be

inspected at intervals of 800 flight cycles; therefore, the adoption of

a 1,600-flight cycle interval for the proposed inspections would allow

some of them to be accomplished concurrently with those of AD 94-03-07.

This will simplify scheduling and eliminate duplication of work for

affected operators. The FAA concurs. In addition to considering the

reasons presented by these commenters, the FAA has reviewed and

approved Revision 1 of Boeing Service Bulletin 767-32-0128, dated March

31, 1994. Among other things, this revised version of the service

bulletin recommends that inspections of the pins, the brake torque arm

bushings, and the brake rod bushings begin within 1,600 flight cycles

and be repeated at intervals of 1,600 flight cycles. Paragraph (a) of

the final rule has been revised to specify a 1,600-flight cycle

inspection interval, and to reference the revised version of the

service bulletin as the appropriate source of service information.

Another commenter requests that the inspections of the bulkhead,

keeper pin, and brake attach pin, as proposed by paragraph (b), be

eliminated. This commenter points out that modification of the brake

rod pin assembly and the brake attach pin retainer, which is required

by AD 94-03-07, has significantly strengthened the brake load path in

this area. There has been no indication that this area continues to be

a problem area once the modification is installed. The FAA concurs with

the commenter's request to delete the proposed inspections. The

requirements of AD 94-03-07 eliminated the cross bolts at the brake rod

attach pin, thereby eliminating one of the failure modes in the brake

load path that had accounted for a significant number of brake loss

incidents. The modification required by AD 94-03-07 improves the brake

load path in the brake-to-brake rod attachment area. In light of this,

the FAA has determined that the inspections proposed in paragraph (b)

of the notice are not necessary, and has deleted them from the final

rule. The FAA notes that Part 2 of Revision 1 of Boeing Service

Bulletin 767-32-0128 provides instructions for inspecting the modified

area for corrosion or damage. Although those inspections may be ``value

added,'' the FAA does not consider them necessary to improve the safety

of the brake system.

One commenter provides an update on the number of airplanes

affected by the proposed AD. The information provided by this commenter

indicates that the worldwide number has risen from 289 airplanes (at

the time the proposal was issued) to 308 airplanes; and the U.S.-

registered number has risen from 71 airplanes to 77 airplanes. The FAA

has revised the economic impact information, below, accordingly.

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.

There are approximately 308 Model 767 series airplanes of the

affected design in the worldwide fleet. The FAA estimates that 77

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

take approximately 10 work hours per airplane to accomplish the

required actions, and that the average labor rate is $55 per work hour.

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

operators is estimated to be $42,350, or $550 per airplane, per

inspection cycle.

The total cost impact figure discussed above is 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.

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 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. App. 1354(a), 1421 and 1423; 49 U.S.C.

106(g); and 14 CFR 11.89.

Sec. 39.13 [Amended]

2. Section 39.13 is amended by adding the following new

airworthiness directive:

94-16-05 Boeing: Amendment 39-8995. Docket 93-NM-218-AD.

Applicability: Model 767 series airplanes equipped with carbon

brakes, certificated in any category.

Compliance: Required as indicated, unless accomplished

previously.

To prevent the failure of components of the main landing gear,

which could severely affect the braking capability of the airplane

while on the ground, accomplish the following:

(a) Within 1,600 flight cycles after the effective date of this

AD, and thereafter at intervals not to exceed 1,600 flight cycles,

conduct inspections to detect cracking and corrosion of the pin that

attaches the brake rod to the brake housing; to detect cracking of

the brake torque arm bushings; and to detect wear of the brake rod

bushings; in accordance with Part 1 of Boeing Service Bulletin 767-

32-0128, Revision 1, dated March 31, 1994. If any discrepancy is

detected in any part, replace or repair the part in accordance with

the compliance schedule specified in Figure 1, Figure 2, or Figure 3

of the service bulletin, as applicable.

Note 1: Inspections, replacement, and repairs performed prior to

the effective date of this AD in accordance with Boeing Service

Bulletin 767-32-0128, dated November 11, 1993, are considered to be

in compliance with this paragraph.

(b) 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.

(c) 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.

(d) The actions shall be done in accordance with Boeing Service

Bulletin 767-32-0128, Revision 1, dated March 31, 1994. 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.

(e) This amendment becomes effective on September 14, 1994.

Issued in Renton, Washington, on August 2, 1994.

Darrell M. Pederson,

Acting Manager, Transport Airplane Directorate, Aircraft Certification

Service.

[FR Doc. 94-19353 Filed 8-12-94; 8:45 am]

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