Airworthiness Directives; Boeing Model 747 Series Airplanes Equipped With General Electric CF6-80C2 Engines

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 94-NM-119-AD]

Airworthiness Directives; Boeing Model 747 Series Airplanes

Equipped With General Electric CF6-80C2 Engines

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 747 series

airplanes. This proposal would require modification of the fire

extinguishing system in the number two engine strut. This proposal is

prompted by reports of chafing of the fire extinguishing tubes in a

certain inboard strut to wing area. The actions specified by the

proposed AD are intended to prevent chafing of the fire extinguishing

tube; such chafing could cause cracking of the tube and consequently

produce a hole in the fire extinguishing tube, which could prevent the

proper distribution of the fire extinguisher agent within the nacelle

in the event of a fire.

DATES: Comments must be received by December 5, 1994.

ADDRESSES: Submit comments in triplicate to the Federal Aviation

Administration (FAA), Transport Airplane Directorate, ANM-103,

Attention: Rules Docket No. 94-NM-119-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 Airplane Directorate, 1601 Lind Avenue, SW., Renton,

Washington.

FOR FURTHER INFORMATION CONTACT:

Tamra Elkins, Aerospace Engineer, FAA, Transport Airplane Directorate,

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

Washington 98055-4056; telephone (206) 227-2669; fax (206) 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 94-NM-119-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-103, Attention: Rules

Docket No. 94-NM-119-AD, 1601 Lind Avenue, SW., Renton, Washington

98055-4056.

Discussion

On June 17, 1992, the FAA issued AD 92-14-07, amendment 39-8289 (57

FR 31433, July 16, 1994), applicable to certain Boeing Model 747 series

airplanes, to require repetitive inspections to detect damage of the

tubes of the engine fire extinguishing system in the number two and

number three engine struts; replacement or repair, if necessary; and

reorientation of the clamp. That Ad also requires modification of the

engine fire extinguishing system in the number two and number three

engine struts, which, when accomplished, terminates the inspection

requirements. The modification was required to be accomplished on all

affected airplanes no later than February 20, 1993. That action was

prompted by multiple reports of the support clamps in the number two

and number three engine struts chafing a hole in the tubes of the

engine fire extinguishing system. The requirements of that AD are

intended to prevent inadequate distribution of the fire extinguishing

agent within the nacelle in the event of a fire.

Since the issuance of that AD, the FAA has received reports of

chafing of the tubes and/or cracking of the rubber blocks that are an

integral part of the clamps in the inboard strut to wing area in the

number two engine strut. (The tube and the rubber blocks were installed

as part of the modification required by AD 92-14-07.) As a result of

the chafing, one of the tubes on one airplane cracked approximately six

inches from the forward end. Investigation revealed that the cracked

tube had a notch near the cracked area of the tube that had been formed

due to contact with a ground stud. This notch may have initiated the

crack in the tube. Further investigation revealed that the rubber

blocks, which support the tubes, were cracked between the stand-off

spacers and the tubes.

The cause of such chafing and cracking has been attributed to

movement between the spacer and the tube. This movement exceeded the

flexibility of the rubber and stressed the rubber block, which

subsequently pinched and tore the rubber block of the clamp. Such

pinching and tearing could cause the clamp to fail and could lead to

chafing of the fir extinguishing tube.

Chafing of the fire extinguishing tube, if not corrected, could

result in cracking of the fire extinguishing tube and consequently

produce a hole in the fire extinguishing tube, which could prevent the

proper distribution of the fire extinguishing agent within the nacelle

in the event of a fire.

The FAA has reviewed and approved Boeing Alert Service Bulletin

747-26A2226, dated June 30, 1994, which describes procedures for

modification of the fire extinguishing system in the number two engine

strut. This modification entails removing and replacing the fire

extinguishing tube with a new, improved tube (for Group 1 and 2

airplanes); removing and reinstalling the existing fire extinguishing

tube (for Group 3 airplanes); and replacing the channel and rubber

blocks; and reworking the forward bracket (for Group 1, 2, and 3

airplanes). This modification would revise the geometry of the rubber

block and the tube, which would increase the flexibility of the rubber

block and would increase the clearance between the tube and the

adjacent ground studs.

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 modification of the fire extinguishing system

in the number two engine strut. The actions would be required to be

accomplished in accordance with the alert service bulletin described

previously.

There are approximately 145 Boeing Model 747 series airplanes

equipped with General Electric CF6-80C2 engines of the affected design

in the worldwide fleet. The FAA estimates that 2 airplanes of U.S.

registry would be affected by this proposed AD, that it would take

approximately 3 work hours per airplane to accomplish the proposed

actions, and that the average labor rate is $55 per work hour. Required

parts would be supplied by the manufacturer at no cost to the

operators. Based on thee figures, the total cost impact of the proposed

AD on U.S. operators is estimated to be $330, or $165 per airplane.

The total 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.

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. 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:

Boeing: Docket 94-NM-119-AD.

Applicability: Model 747 series airplanes equipped with General

Electric CF6-80C2 engines; as listed in Boeing Alert Service

Bulletin 747-26A2226, dated June 30, 1994; certificated in any

category.

Compliance: Required as indicated, unless accomplished

previously.

To ensure proper distribution of the fire extinguisher agent

within the nacelle in the event of a fire, accomplish the following:

(a) Within 6 months after the effective date of this AD, modify

the fire extinguishing system in the number two engine strut, in

accordance with the Accomplishment Instructions of Boeing Alert

Service Bulletin 747-26A2226, dated June 30, 1994.

(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

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 October 3, 1994.

Darrell M. Pederson,

Acting Manager, Transport Airplane Directorate, Aircraft Certification

Service.

[FR Doc. 94-24873 Filed 10-6-94; 8:45 am]

BILLING CODE 4910-13-P