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

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URL: https://www.frixlaw.com/law-library/documents/fr%3A94-19353

## Record

- **Collection:** Federal Register
- **Document type:** Uncategorized Document
- **Published:** August 15, 1994

## Text

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]
BILLING CODE 4910-13-U

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Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A94-19353. Public record. Not legal advice.