Airworthiness directives: Boeing,
[Federal Register: November 23, 1998 (Volume 63, Number 225)]
[Proposed Rules]
[Page 64659-64661]
From the Federal Register Online via GPO Access [wais.access.gpo.gov]
[DOCID:fr23no98-31]
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
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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 filedin 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.
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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
-
The authority citation for part 39 continues to read as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701.
Sec. 39.13 [Amended]
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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. 98-31174Filed11-20-98; 8:45 am]
BILLING CODE 4910-13-U
