[Federal Register Volume 59, Number 156 (Monday, August 15, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-19353]


[[Page Unknown]]

[Federal Register: August 15, 1994]


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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