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RULES and REGULATIONS DEPARTMENT OF TRANSPORTATION 14 CFR Part 39 [Docket No. 86
-NM
- 175
-AD; Amdt. 39
- 5506] Airworthiness Directives; Boeing Models 737
- 100 and 737
-200 Series Airplanes Wednesday, January 7, 1987 AGENCY: Federal Aviation Administration (FAA), DOT. ACTION: Final rule. SUMMARY: This amendment adopts a new airworthiness directive (AD), applicable to certain Boeing Model 737 airplanes, which requires replacement of certain underwing fuel tank access covers with stronger, fire
-resistant c overs. This action is prom pted by one incident of cover penetration which resulted in a fire and total loss of the airplane. EFFECTIVE DATE: February 9, 1987. ADDRESSES: The applicable service information, when issued, may be obtained from the Boeing Commercial Airplane Com

pany, P.O. Box 3707, Seattle, Washington 98124. This information may be examined at the FAA, Northwest Mountain Region, 17900 Pacific Highway South, Seattle, Washington, or the Seattle Aircraft Certific ation Office, 9010 East Marginal Way South, Seattle, Washington. FOR FURTHER INFORMATION CONTACT: Mr. William M. Perrella, Airframe Branch, ANM
- 120S; telephone (206) 431
- 1922. Mailing address: FAA, Northwest Mountain Region, 17900 Pacific Highway South, C
- 68966, Seattle, Washington 98168. SUPPLEMENTARY INFORMATION: A proposal to amend Part 39 of the Federal Aviation Regulations to include an airworthiness directive which requires certain fuel tank access covers to be replaced by improved types with more im pact resistance, was published in the Federal Register on September 2, 1986 ( 51 FR 31134) . The comment period for the proposal closed on October 20, 1986. Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received. The Air Transport Association (ATA) of America requested extension of the com pliance time to allow cover installation at least one year after receipt of a service bulletin and parts from the manufacturer. The FAA expects this final rule to become effective concurrent with the release of the Boeing service bulletin on this subject. Production of parts is anticipated to begin about the same time. Therefore, the FAA has determined that the compliance time of one year, as proposed, is an appropriate amount of time for operators to receive the service bulletin and accom plish the required installation. One operator requested the com pliance time be extended to two years based on his engine maintenance program. While properly maintained engines should not suffer the failure experienced in Manchester, England, there is, never-2

theless, a remote possibility that such a failure could occur. Since the modification is relatively easy, the FAA has determined that a com

pliance period of one year will not impose an undue burden on operators. In the interest of safety, considering the potential effect of cover plate failure, the FAA considers a two -year period to represent an unacceptable exposure time. Several comments were received from the United Kingdom Civil Aviation Authority (CAA), which agreed that the AD wa s necessary. In addition, it had some reservations about the level of imp act resistance specified in the proposed rule and, further, stated that additional covers, which are in the engine or tire burst zones, should be included. This latter concern was expressed by one operator as well. The FAA does not fully agree. The level of im pact resistance specified in the rule is considered more than adequate to prevent penetration by a failed com bustion chamber, as well as other debris of mo derate velocity and energy. Some rare engine failure modes result in high energy debris, against which no practical design measures can protect. As to increasing the number of covers, the FAA has reviewed the service experience on the Model 737 and finds no substantiation of an unsafe condition at other loc ations. Nevertheless, the FAA has determined that an im provement in impact resistance is warranted and a proposed change to FAR 121 is being considered w hich would require all transport aircraft to install impact resistant covers in areas susceptible to damage. Comments were also received from the National Transportation Safety Board (NTSB), w hich supported the AD. 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 as proposed. It is estimated that 396 airplanes of U.S. registry will be affected by this AD, and that approximately 16 manhours per airplane will be required to replace the affected covers. Based on an estimated replacement cost of $500 per cover and an average labor cost of $40 per manhour, the total cost impact of this AD to U.S. operators is estimated to be $1,045,440. For the reasons discussed above, the FAA has determined that this regulation is not considered to be major under Executive Order 12291 or significant under DOT Regulatory Policies and Procedures (44 FR 11034; February 26, 1979); and it is further certified under the criteria of the Regulatory Flexibility Act that this rule will not have a significant economic impact on a substantial number of small entities because few, if any, Boeing Model 737 airplanes are operated by small entities. A final evaluation has been prepared for this regulation and has been placed in the docket. List of Subjects in 14 CFR Part 39 Aviation safety, Aircraft. Adoption of the Amendment PART 39

— [AMENDED] 14 CFR § 39.13 Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends § 39.13 of Part 39 of the Federal Aviation Regulations as follows: 1. The authority citation for Part 39 continues to read as follows: Authority: 49 U.S.C. 1354(a), 1421 and 1423; 49 U.S.C. 106(g) (Revised Pub. L. 97
-449, January 12, 1983); and 14 CFR 11.89.3

2. By adding the following new airworthiness directive: Boeing: Applies to all Models 737
- 100 and 737
-200 series airplanes, certificated in any c ategory. To minimize the hazard of lower wing surface fuel tank access cover penetration due to im pact from low energy engine debris, accomplish the following, unless already accomplished. A. Within the next year after the effective date of this AD, replace the lower wing surface fuel tank access covers located immediately inboard and outboard of each engine (total of four per airplane), with covers having im pact resistance equivalent to that of 2 024
-T3 aluminum 0.140
-inch thick, as approved by the Manager, Seattle Aircraft Certification Office, FAA, Northwest Mountain Region. The replacement c overs must also be fire resistant, as defined in the Federal Aviation Regulations, Part 1. B. An alternate means of com pliance or adjustment of

the compliance time, which provides an acceptable level of safety, may be used when approved by the Manager, Se attle Aircraft Certification Office, FAA, Northwest Mountain Region. C. Special flight permits may be issued in accordance with FAR 21.197 and 21.199 to operate airplanes to a base for the accomplishment of the modifications required by this AD. This amendment becomes effective February 9, 1987. Issued in Seattle, Washington, on December 29, 1986. Frederick M. Isaac, Acting Director, Northwest Mountain Region.
52 FR 518
- 01