Airworthiness Directives; Boeing Model 737-300, -400, and -500 Series Airplanes

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 93-NM-146-AD; Amendment 39-8858; AD 94-06-11]

Airworthiness Directives; Boeing Model 737-300, -400, and -500

Series Airplanes

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 737-300, -400, and -500 series

airplanes, that requires modification of the leading edge slat access

panel and internal structure at Front Spar Station (FSS) 250.663. This

amendment is prompted by reports that fuel leaking from the fuel line

at FSS 250.663 flowed through a drain hole in a slat access panel and

leaked into the turbine exhaust area. The actions specified by this AD

are intended to prevent drainage from such a fuel leak into the turbine

exhaust area, which could cause an external fire under the wing.

DATES: Effective April 21, 1994.

The incorporation by reference of certain publications listed in

the regulations is approved by the Director of the Federal Register as

of April 21, 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: Stephen Bray, Aerospace Engineer,

Propulsion Branch, ANM-140S, FAA, Transport Airplane Directorate,

Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton,

Washington 98055-4056; telephone (206) 227-2681; fax (206) 227-1181.

SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal

Aviation Regulations to include an airworthiness directive (AD) that is

applicable to certain Boeing Model 737-300, -400, and -500 series

airplanes was published in the Federal Register on November 16, 1993

(58 FR 60415). That action proposed to require modification of the

leading edge slat access panel and internal structure at Front Spar

Station (FSS) 250.663.

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.

Another commenter suggests that certain wording used in the

preamble to the notice to describe the unsafe condition be clarified.

This commenter notes that the preamble described the proposed actions

as intended to ``prevent such a fuel leak [from causing an external

fire under the wing];'' however, the actual intent of the proposed

actions is to ``prevent drainage from such a fuel leak into the turbine

exhaust area [which could cause an external fire under the wing].'' The

FAA concurs with the commenter' suggestion and has revised certain

wording in the preamble to this final rule accordingly.

This commenter also suggests that the preamble to the notice

contained an inaccurate statement in the Discussion section, which

indicated that ``* * *. The resultant fire could spread from the

turbine exhaust area to the strut and, subsequently, could ignite fuel

within the strut.'' The commenter points out that the strut drain

system would route leakage clear of the exhaust area and, therefore,

the strut would not contain fuel to be ignited. The commenter suggests

that condition being addressed is the result of fuel leakage draining

from the wing leading edge slat access panel outboard of the strut. The

proposed corrective modification involves closing the slat access panel

drain and rerouting the drainage from this area into the strut drain

system, which will ensure that the drainage is discharged clear of the

turbine exhaust area. The FAA does not concur that this statement was

totally inaccurate. However, in order to provide some clarification of

this issue, the FAA considers that a more precise description of the

situation prompting the addressed unsafe condition is ``* * *. The

resultant fire could spread from the turbine exhaust area to the wing

leading edge slat, and subsequently spread to the wing front spar at

FSS 250.663.''

This same commenter requests that the FAA delay issuance of the

rule until a revised version of the referenced service bulletin is

issued in mid-April. This revised service bulletin will include

procedures for an optional method of closing the drain hole in the slat

access panel. The FAA does not concur that delaying issuance of this

rule, for the reasons cited by the commenter, is appropriate. If a

revised service bulletin is released sometime in the future, the use of

it as an alternative method for complying with this rule may be

requested under the provisions of paragraph (b) of this final rule.

Several commenters request that the proposed compliance time of 12

months be extended to 60 months, so that the modification can be

accomplished during a regularly scheduled ``heavy'' maintenance

interval when the airplane is brought to the main maintenance base for

an extended hold. These commenters point out that adoption of the

proposed 12-month compliance time would require affected operators to

schedule special times for the accomplishment of this modification, at

significant additional expense. These commenters consider that such an

extension is justified since a fuel leak of the type addressed by the

proposed AD is limited to ground operations after the engines have been

shut down; the risk of injury to personnel under this scenario is

considerably less than a potential fire threat during airborne

operations. The FAA concurs that the compliance time can be extended

somewhat. Upon reconsideration, the FAA finds that the proposed 12-

month compliance time may impose an undue economic burden on affected

operators. The FAA has determined that extending the compliance time

for modification to 24 months will not compromise safety. In addition,

it will allow operators to accomplish the modification during a

regularly scheduled ``C'' check maintenance interval at a main base,

where special equipment and trained maintenance personnel will be

available, if required. Paragraph (a) of the final rule has been

revised 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 950 Model 737-300, -400, and -500 series

airplanes of the affected design in the worldwide fleet. The FAA

estimates that 400 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. The cost of required parts is expected to be negligible.

Based on these figures, the total cost impact of the AD on U.S.

operators is estimated to be $220,000, or $550 per airplane.

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 14 CFR part

39 of the Federal Aviation Regulations 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:

94-06-11 Boeing: Amendment 39-8858. Docket 93-NM-146-AD.

Applicability: Model 737-300, -400, and -500 series airplanes,

line position 1001 through 1976 inclusive, 1978 through 2183

inclusive, 2185 through 2186 inclusive, and 2188 through 2193

inclusive; certificated in any category.

Compliance: Required as indicated, unless accomplished

previously.

To prevent drainage from a fuel line leak within the wing

leading edge from entering the turbine exhaust area, which could

cause an external fire under the wing, accomplish the following:

(a) Within 24 months after the effective date of this AD, modify

the leading edge slat access panel and internal structure at Front

Spar Station (FSS) 250.663 in accordance with Boeing Service

Bulletin 737-57-1221, dated August 6, 1992.

(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: 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

Federal Aviation Regulations (FAR) 21.197 and 21.199 to operate the

airplane to a location where the requirements of this AD can be

accomplished.

(d) The modification shall be done in accordance with Boeing

Service Bulletin 737-57-1221, dated August 6, 1992. 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 April 21, 1994.

Issued in Renton, Washington, on March 10, 1994.

Darrell M. Pederson,

Acting Manager, Transport Airplane Directorate, Aircraft Certification

Service.

[FR Doc. 94-6068 Filed 3-21-94; 8:45 am]

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