Airworthiness Directives; Boeing Model 747 Series Airplanes

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 93-NM-189-AD]

Airworthiness Directives; Boeing Model 747 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 747 series

airplanes. This proposal would require inspections to detect cracking

in certain fuselage upper deck tension ties, and repair or modification

of any cracked tension ties. This proposal is prompted by reports of

fatigue cracking in tension ties. The actions specified by the proposed

AD are intended to prevent failure of two or more tension ties and the

resultant rapid decompression of the airplane.

DATES: Comments must be received by March 21, 1994.

ADDRESSES: Submit comments in triplicate to the Federal Aviation

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

Attention: Rules Docket No. 93-NM-189-AD, 1601 Lind Avenue, SW.,

Renton, Washington 98055-4056. Comments may be inspected at this

location between 9 a.m. and 3 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: Steven C. Fox, Aerospace Engineer,

Airframe Branch, ANM-120S, FAA, Transport Airplane Directorate, Seattle

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

Washington 98055-4056; telephone (206) 227-2777; 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 93-NM-189-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. 93-NM-189-AD, 1601 Lind Avenue, SW., Renton, Washington

98055-4056.

Discussion

Recently, the FAA has received reports of fatigue cracking in the

tension ties on several Boeing Model 747 series airplanes. Most of the

cracks were found in the aft channel of the tension tie. These cracks

usually occurred in the upper flange of the aft channel of the tension

tie. Only one crack was found in the forward channel of the tension

tie. The cause of this fatigue cracking has been attributed to the

tension ties bending under cabin pressurization loads. This condition,

if not corrected, could result in rapid decompression of the airplane

in the event of failure of two or more tension ties.

These reports of fatigue cracks were received in response to the

Supplemental Structural Inspection Program, which was required to be

implemented by AD 93-06-01, Amendment 39-8526 (58 FR 19571, April 15,

1993). The purpose of that AD is to implement an inspection program

that detects the potential for cracking in specific areas of the

airplane that are critical for flight safety. Whenever cracks are found

in a Structural Significant Item, the FAA takes rulemaking action to

correct these findings of an unsafe condition. This proposal is in

response to such a finding.

On September 4, 1984, the FAA issued AD 84-19-01, amendment 39-4913

(49 FR 36365, September 17, 1984), to require inspections of the

tension tie at body station (BS) 760 on a certain group of Model 747

series airplanes, and at BS 780 on certain other Model 747 series

airplanes. The inspections proposed by this rulemaking action do not

retract the inspection requirements of that AD.

The FAA has reviewed and approved Boeing Service Bulletin 747-53-

2371, dated July 29, 1993, that describes procedures for repetitive

detailed visual inspections of the outboard ends of certain tension

ties, and repair or modification of cracked tension ties. This

modification entails trimming the cracked portion of the channel of the

tension tie.

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 detailed visual inspections of the

outboard ends of certain tension ties, and repair or modification of

cracked tension ties. The actions would be required to be accomplished

in accordance with the service bulletin described previously.

There are approximately 203 Boeing Model 747 series airplanes of

the affected design in the worldwide fleet. The FAA estimates that 113

airplanes of U.S. registry would be affected by this proposed AD, that

it would take approximately 5 work hours per airplane to accomplish the

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

Based on these figures, the total cost impact of the proposed AD on

U.S. operators is estimated to be $31,075, or $275 per airplane. This

total cost figure assumes that no operator has yet accomplished the

proposed requirements of this AD action.

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 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:

Boeing: Docket 93-NM-189-AD.

Applicability: Model 747 series airplanes, as listed in Boeing

Service Bulletin 747-53-2371, dated July 29, 1993, certificated in

any category.

Compliance: Required as indicated, unless accomplished

previously.

To prevent rapid decompression of the airplane due to failure of

two or more tension ties, accomplish the following:

(a) Prior to the accumulation of 1,000 flight cycles after the

effective date of this AD, unless accomplished previously within the

last 2,000 flight cycles, perform a detailed visual inspection to

detect cracking of the outboard end tension ties, in accordance with

Boeing Service Bulletin 747-53-2371, dated July 29, 1993.

(1) If no cracking is detected, repeat the inspection thereafter

at intervals not to exceed 3,000 flight cycles until the repair or

modification required by paragraph (a)(2) of this AD is

accomplished.

(2) If any cracking is detected, prior to further flight, repair

or modify the cracked tension tie in accordance with the service

bulletin. Accomplishment of this repair or modification terminates

the repetitive inspection requirement of paragraph (a) of this AD.

Note 1: Although AD 84-19-01, amendment 39-4913, requires

inspections of the tension ties at body station (BS) 760 on a

certain group of Model 747 series airplanes, and at BS 780 on

certain other Model 747 series airplanes, the inspections required

by this AD do not retract the inspection requirements of that AD.

(b) Prior to the accumulation of 10,000 flight cycles following

repair or modification of any tension tie, perform a detailed visual

inspection to detect cracking of the repaired or modified outboard

end tension tie in accordance with Boeing Service Bulletin 747-53-

2371, dated July 29, 1993.

(1) If no cracking is detected, repeat this inspection

thereafter at intervals not to exceed 6,000 flight cycles.

(2) If any cracking is detected, prior to further flight, repair

or modify in accordance with the service bulletin, and repeat the

inspection required by paragraph (b) of this AD.

(c) 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 2: Information concerning the existence of approved

alternative methods of compliance with this AD, if any, may be

obtained from the Seattle ACO.

(d) Special flight permits may be issued in accordance with FAR

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 January 18, 1994.

John J. Hickey,

Acting Manager, Transport Airplane Directorate, Aircraft Certification

Service.

[FR Doc. 94-1542 Filed 1-21-94; 10:00 am]

BILLING CODE 4910-13-U