[Federal Register Volume 63, Number 225 (Monday, November 23, 1998)]
[Proposed Rules]
[Pages 64659-64661]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-31174]


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

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 98-NM-275-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 777 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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

SUMMARY: This document proposes the adoption of a new airworthiness 
directive (AD) that is applicable to certain Boeing Model 777 series 
airplanes. This proposal would require repetitive inspections of the 
safety spring wear plate doublers attached to the auxiliary power unit 
(APU) firewall, measurement of wear of the doublers, and follow-on 
actions, if necessary. This proposed AD also would provide for optional 
terminating action for the repetitive inspections. This proposal is 
prompted by reports indicating that excessive wear was found on the 
safety spring wear plate doublers on the APU firewall of Boeing Model 
777 series airplanes. The actions specified by the proposed AD are 
intended to detect and correct wear of the safety spring wear plate 
doublers on the APU firewall, which could result in a hole in the APU 
firewall, and consequent decreased fire protection capability.

DATES: Comments must be received by January 7, 1999.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 98-NM-275-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

[[Page 64660]]

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

FOR FURTHER INFORMATION CONTACT: Ed Hormel, Aerospace Engineer, 
Propulsion Branch, ANM-140S, FAA, Transport Airplane Directorate, 
Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056; telephone (425) 227-2681; 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 98-NM-275-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. 98-NM-275-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    The FAA has received several reports indicating that excessive wear 
was found on the titanium safety spring wear plate doublers on the 
auxiliary power unit (APU) firewall of Boeing Model 777 series 
airplanes. Several of the airplanes on which the excessive wear 
condition was found had at least 40 percent wear of one or both of the 
doublers. In one case, the wear penetrated 0.060 inch into the 0.063-
inch-thick doubler. Such excessive wear has been attributed to fretting 
between the tip of the APU door spring and the doubler. Excessive wear 
of the safety spring wear plate doublers, if not corrected, could 
result in a hole in the APU firewall, and consequent decreased fire 
protection capability.

Explanation of Relevant Service Information

    The FAA has reviewed and approved Boeing Alert Service Bulletin 
777-53A0018, dated June 29, 1998, which describes procedures for 
repetitive inspections of the safety spring wear plate doublers on the 
APU firewall, measurement of wear of the doublers, and follow-on 
actions, if necessary. Those follow-on actions include repair, or 
replacement of the existing titanium doublers with new stainless steel 
doublers. Replacement of the existing doublers with new stainless steel 
doublers would eliminate the need for the repetitive inspections. If 
wear is detected that is through the wear plate doubler and into or 
through the APU firewall, the alert service bulletin specifies to 
contact Boeing for repair instructions. Accomplishment of the actions 
specified in the alert service bulletin is intended to adequately 
address the identified unsafe condition.

Explanation of Requirements of Proposed Rule

    Since an unsafe condition has been identified that is likely to 
exist or develop on other products of this same type design, the 
proposed AD would require repetitive inspections of the safety spring 
wear plate doublers attached to the APU firewall, measurement of wear 
of the doublers, and follow-on actions, if necessary. The actions would 
be required to be accomplished in accordance with the alert service 
bulletin described previously, except as discussed in the paragraph 
entitled ``Differences Between Proposed Rule and Alert Service 
Bulletin.''
    The FAA has determined that, if wear is detected that is through 
the wear plate doubler and into or through the APU firewall, flight 
with such damage (i.e., a hole in the doubler or APU firewall) is 
permitted, provided that a temporary repair is accomplished within 20 
days after the damage is discovered. The FAA finds that 20 days is 
adequate to permit the repair to be accomplished at an authorized 
repair station. The FAA finds that allowing flight to continue for 20 
days following detection of such damage is acceptable because there 
have been no reports indicating wear through the doubler or into the 
firewall on any in-service airplane, and no reports of any fire in the 
APU compartment of any Model 777 series airplane. This determination 
also is based upon the fact that the hole is caused by the tip of the 
APU door spring. When the APU doors are in the closed position, the tip 
of the door spring blocks the hole. The blockage of the hole by the 
spring is sufficient to prevent hazardous quantities of air, flammable 
fluids, or flames from passing through the hole. If extended operation 
(i.e., more than 20 days) is permitted with such a hole in the 
firewall, the size of the hole would continue to increase to a point at 
which the door spring no longer would prevent hazardous quantities of 
air, flammable fluids, or flames from passing through the hole.
    The FAA also has determined that permanent replacement of any 
repaired wear plate doubler must be accomplished within 4,000 flight 
cycles after installation of the temporary repair. This determination 
is based on the fact that such a hole would not affect the structural 
integrity of the airplane. The FAA considers that a compliance time of 
4,000 flight cycles is conservative (relative to the resistance to wear 
of the temporary repair) and sufficient to ensure the safety of the 
transport airplane fleet.

Differences Between Proposed Rule and Alert Service Bulletin

    Operators should note that, although the alert service bulletin 
specifies that the manufacturer may be contacted for disposition of 
certain repair conditions, this proposal would require the repair of 
those conditions to be accomplished in accordance with a method 
approved by the FAA.

Cost Impact

    There are approximately 156 airplanes of the affected design in the 
worldwide fleet. The FAA estimates that 35 airplanes of U.S. registry 
would be affected by this proposed AD.
    It would take approximately 2 work hours per airplane to accomplish 
the proposed inspection, at an average labor rate of $60 per work hour. 
Based on these figures, the cost impact of the inspection proposed by 
this AD on U.S. operators is estimated to be $4,200, or $120 per 
airplane, per inspection cycle.
    The cost impact figure discussed above is based on assumptions that 
no operator has yet accomplished any of the proposed requirements of 
this AD action, and that no operator would accomplish those actions in 
the future if this AD were not adopted.

[[Page 64661]]

    Should an operator be required to accomplish the temporary repair, 
it would take approximately 2 work hours per airplane to accomplish the 
repair, at an average labor rate of $60 per work hour. Based on these 
figures, the cost impact of the temporary repair action is estimated to 
be $120 per airplane.
    Should an operator be required or elect to accomplish the 
replacement of the wear plate doublers, it would take approximately 3 
work hours per airplane to accomplish the replacement, at an average 
labor rate of $60 per work hour. Based on these figures, the cost 
impact of replacement of the wear plate doublers is estimated to be 
$180 per airplane.

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 98-NM-275-AD.

    Applicability: Model 777 series airplanes, line numbers 001 
through 156 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 (g) 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 detect and correct wear of the safety spring wear plate 
doublers on the auxiliary power unit (APU) firewall, which could 
result in a hole in the APU firewall, and consequent decreased fire 
protection capability, accomplish the following:
    (a) Perform a visual inspection of the two safety spring wear 
plate doublers on the APU firewall, and measure any wear of the 
doublers, in accordance with Boeing Alert Service Bulletin 777-
53A0018, dated June 29, 1998, at the time specified in paragraph 
(a)(1), (a)(2), or (a)(3) of this AD, as applicable.
    (1) For airplanes that have accumulated 6,000 total flight hours 
or less as of the effective date of this AD: Inspect and measure 
prior to the accumulation of 6,300 total flight hours.
    (2) For airplanes that have accumulated between 6,001 and 10,000 
total flight hours as of the effective date of this AD: Inspect and 
measure within 30 days after the effective date of this AD.
    (3) For airplanes that have accumulated 10,001 total flight 
hours or more as of the effective date of this AD: Inspect and 
measure within 10 days after the effective date of this AD.
    (b) If, during the inspection required by paragraph (a) of this 
AD, the wear on each doubler measures less than 0.045 inch, repeat 
the inspection and measurement required by paragraph (a) of this AD 
thereafter at intervals not to exceed 60 days, in accordance with 
Boeing Alert Service Bulletin 777-53A0018, dated June 29, 1998.
    (c) If, during the inspection required by paragraph (a) of this 
AD, the wear on either doubler measures greater than or equal to 
0.045 inch: Except as provided by paragraph (d) of this AD, repeat 
the inspection and measurement required by paragraph (a) of this AD 
thereafter at intervals not to exceed 30 days, in accordance with 
Boeing Alert Service Bulletin 777-53A0018, dated June 29, 1998.
    (d) If, during the inspection required by paragraph (a) of this 
AD, any wear penetrates either doubler: Within 20 days after 
detection of the wear, accomplish the requirements of either 
paragraph (d)(1) or (d)(2) of this AD, in accordance with Boeing 
Alert Service Bulletin 777-53A0018, dated June 29, 1998.
    (1) Install a temporary stainless steel patch on both doublers, 
and within 4,000 flight cycles after installation of the temporary 
patch, accomplish the requirements of paragraph (d)(2) of this AD.
    (2) Replace both existing wear plate doublers of the APU 
firewall with new stainless steel wear plate doublers in accordance 
with the alert service bulletin. Such replacement constitutes 
terminating action for the repetitive inspection requirements of 
paragraphs (b) and (c) of this AD.
    (e) If wear penetrates into or through the APU firewall: Within 
20 days after detection of the wear, repair any damage to the APU 
firewall in accordance with a method approved by the Manager, 
Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane 
Directorate.
    (f) Replacement of the existing wear plate doublers of the APU 
firewall with new stainless steel wear plate doublers, in accordance 
with Boeing Alert Service Bulletin 777-53A0018, dated June 29, 1998, 
constitutes terminating action for the repetitive inspection 
requirements of paragraphs (b) and (c) of this AD.
    (g) 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. 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.

    (h) 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 November 16, 1998.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 98-31174 Filed 11-20-98; 8:45 am]
BILLING CODE 4910-13-U