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

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 94-NM-30-AD]

Airworthiness Directives; Boeing Model 747 Series Airplanes

Equipped With General Electric CF6 Series Engines

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the supersedure of an existing

airworthiness directive (AD), applicable to certain Boeing Model 747

series airplanes, that currently requires inspections of the strut skin

in the area of the precooler exhaust vent for cracks on the inboard and

outboard struts, and repair, if necessary. This action would require

inspections of an expanded area for certain airplanes, and inspections

of airplanes on which a skin doubler has been installed as terminating

action for the existing AD. This proposal is prompted by reports of

strut skin fatigue cracks and heat damage found aft of the edges of

skin doublers installed on certain Model 747 series airplanes. The

actions specified by the proposed AD are intended to prevent separation

of an engine due to overheating and subsequent cracking of the engine

strut.

DATES: Comments must be received by August 8, 1994.

ADDRESSES: Submit comments in triplicate to the Federal Aviation

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

Attention: Rules Docket No. 94-NM-30-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: Tim Backman, Aerospace Engineer,

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

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

98055-4056; telephone (206) 227-2776; 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-30-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-30-AD, 1601 Lind Avenue, SW., Renton, Washington

98055-4056.

Discussion

On January 28, 1987, the FAA issued AD 87-04-21, Amendment 39-5543

(52 FR 3793, February 6, 1987), applicable to certain Boeing Model 747

series airplanes, to require repetitive inspections of the strut skin

in the area of the precooler exhaust vent to detect cracks on the

inboard and outboard struts, and repair, if necessary. That action also

provides for an optional terminating modification (installation of

frame stiffeners and skin doublers) for the repetitive inspections.

That action was prompted by reports of extensive damage to struts on

several airplanes. The requirements of that AD are intended to prevent

separation of an engine due to overheating and subsequent cracking of

the engine strut.

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

fatigue cracks found in the strut skin and heat damage found aft of the

edges of skin doublers. These skin doublers had been installed on

certain Model 747 series airplanes as terminating action for certain

requirements contained in AD 87-04-21 and AD 90-06-06, amendment 39-

6490 (55 FR 8374, March 7, 1990). (AD 90-06-06 requires, in part,

incorporation of certain structural modifications specified in the

original issue, Revision 1, or Revision 2 of Boeing Service Bulletin

747-54-2091.) Further, cracking of the skin doublers and the underlying

number 3 stringer also was found on one of these airplanes.

Subsequently, the FAA has reviewed and approved Boeing Service

Bulletin 747-54-2091, Revision 5, dated April 26, 1990, that describes

procedures for a visual inspection of the strut skin and internal

structure in the area of the precooler exhaust vent for cracks, heat

discoloration, and wrinkles on the inboard and outboard struts of

certain airplanes, and on the outboard struts of certain other

airplanes. The service bulletin also describes procedures for

repetitive inspections if no crack, heat discoloration, or wrinkle is

found; and installation of a skin doubler if any crack, heat

discoloration, or wrinkle is found.

The FAA finds that the inspection areas specified in the Boeing

service bulletin must be expanded since cracks and heat damage have

been reported in locations beyond those inspection areas.

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 supersede AD 87-04-21 to require the following:

1. For airplanes on which a frame stiffener and a skin doubler

specified in certain revisions of Boeing Service Bulletin 747-54-2091

have been installed: Repetitive visual inspections to detect cracks,

heat discoloration, or wrinkles of the strut skin and internal

structure in the area of the precooler exhaust vent from the edge of

the skin doubler to nacelle station (NAC STA) 300 on the inboard and

outboard struts, and repair, if necessary. This inspection area has

been expanded beyond the zone described in Revision 5 of the service

bulletin to cover a 30-inch width from the doubler edge to NAC STA 300.

(This inspection zone excludes the area covered by the skin doubler.)

2. For airplanes on which a frame stiffener and a skin doubler

specified in certain revisions of Boeing Service Bulletin 747-54-2091

have not been installed: Repetitive visual inspections to detect

cracks, heat discoloration, or wrinkles of the strut skin and internal

structure in the area of the precooler exhaust vent from NAC STA 230 to

NAC STA 300 on the inboard and outboard struts, and repair, if

necessary. This inspection area has been expanded beyond the zone

described in Revision 5 of the service bulletin to cover a 30-inch

width from NAC STA 230 to NAC STA 300.

The actions would be required to be accomplished in accordance with

procedures described in the service bulletin described previously.

There are approximately 250 Model 747 series airplanes of the

affected design in the worldwide fleet. The FAA estimates that 4

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

The inspections that were previously required by AD 87-04-21, and

retained in this AD, will take approximately 4 work hours per airplane

to accomplish, at an average labor rate of $55 per work hour. Based on

these figures, the total cost impact of that inspection requirement on

U.S. operators is estimated to be $880, or $220 per airplane, per

inspection cycle.

The new inspections that would be added by this AD action would

take approximately 4 work hours per airplane to accomplish, at an

average labor rate of $55 per work hour. Based on these figures, the

total cost impact of the proposed inspection requirements of this AD on

U.S. operators is estimated to be $880, or $220 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 removing amendment 39-5543 (52 FR

3793, February 6, 1987), and by adding a new airworthiness directive

(AD), to read as follows:

Boeing: Docket 94-NM-30-AD. Supersedes AD 87-04-21, Amendment 39-

5543.

Applicability: Model 747 series airplanes equipped with General

Electric CF6 series engines, certificated in any category.

Compliance: Required as indicated, unless accomplished

previously.

To prevent separation of an engine due to overheating and

subsequent cracking of the engine strut, accomplish the following:

(a) For airplanes listed in Boeing Service Bulletin 747-54-2091,

Revision 1, dated October 22, 1984: Prior to the accumulation of

10,000 total hours time-in-service, or within the next 7\1/2\ months

after March 13, 1987 (the effective date of AD 87-04-21, Amendment

39-5543), whichever occurs later, perform a visual inspection to

detect cracks of the strut skin in the area of the precooler exhaust

vent on the inboard and outboard struts of Group 1 airplanes, and on

the outboard struts of Group 2 airplanes, as defined in the service

bulletin, in accordance with Boeing Service Bulletin 747-54-2091,

Revision 1, dated October 22, 1984; Revision 2, dated March 24,

1988; Revision 3, dated July 27, 1989; Revision 4, dated December

14, 1989; or Revision 5, dated April 26, 1990. After the effective

date of this AD, the inspection shall be accomplished in accordance

with paragraph (b) of this AD.

(1) If no crack is found, repeat the inspection required by

paragraph (a) of this AD thereafter at intervals not to exceed 15

months, until the inspection required by paragraph (b) or (c) of

this AD, as applicable, is accomplished.

(2) If any crack is found, prior to further flight, repair in

accordance with FAA-approved data, and repeat the inspection

required by paragraph (a) of this AD thereafter at intervals not to

exceed 15 months, until the inspection required by paragraph (b) or

(c) of this AD, as applicable, is accomplished.

(b) For airplanes on which a frame stiffener and a skin doubler

have not been installed during production or in accordance with

Boeing Service Bulletin 747-54-2091, Revision 1, dated October 22,

1984; Revision 2, dated March 24, 1988; Revision 3, dated July 27,

1989; Revision 4, dated December 14, 1989; or Revision 5, dated

April 26, 1990: Perform a visual inspection to detect cracks, heat

discoloration, or wrinkles of the strut skin and internal structure

in the area of the precooler exhaust vent from nacelle station (NAC

STA) 230 to NAC STA 300 on the inboard and outboard struts of Group

1 airplanes and on the outboard struts of Group 2 airplanes, in

accordance with the inspection procedures described in Figure 3 of

Boeing Service Bulletin 747-54-2091, Revision 5, dated April 26,

1990; at the time specified in paragraph (b)(1) or (b)(2) of this

AD, whichever occurs later. Accomplishment of this inspection

terminates the repetitive inspections required by paragraph (a) of

this AD.

(1) Prior to the accumulation of 10,000 total hours time-in-

service on the airplane strut, or within 120 days after the

effective date of this AD, whichever occurs later. Or

(2) Within 12 months after the immediately preceding inspection

accomplished in accordance with paragraph (a) of this AD.

Note 1: Paragraph (b) of this AD specifies an inspection zone

that is expanded beyond the zone described in Revision 5 of the

service bulletin to cover a 30-inch width from NAC STA 230 to NAC

STA 300.

(c) For airplanes on which a frame stiffener and a skin doubler

have been installed during production or in accordance with Boeing

Service Bulletin 747-54-2091, Revision 1, dated October 22, 1984;

Revision 2, dated March 24, 1988; Revision 3, dated July 27, 1989;

Revision 4, dated December 14, 1989; or Revision 5, dated April 26,

1990: Within 120 days after the effective date of this AD, perform a

visual inspection to detect cracks, heat discoloration, or wrinkles

of the strut skin and internal structure in the area of the

precooler exhaust vent from the edge of the doubler to NAC STA 300

on the inboard and outboard struts of Group 1 airplanes and on the

outboard struts of Group 2 airplanes, in accordance with the

inspection procedures described in Figure 3 of Boeing Service

Bulletin 747-54-2091, Revision 5, dated April 26, 1990.

Note 2: Paragraph (c) of this AD specifies an inspection zone

that is expanded beyond the zone described in Revision 5 of the

service bulletin to cover a 30-inch width from the doubler edge to

NAC STA 300.

(d) If no crack, heat discoloration, or wrinkle is found during

the inspection required by paragraph (b) or (c) of this AD, repeat

that inspection thereafter at intervals not to exceed 15 months.

(e) If any crack, heat discoloration, wrinkle, or previously

stop-drilled crack is found during the inspection required by

paragraph (b) or (c) of this AD, prior to further flight, repair

using either the small skin doubler and frame stiffener or the large

skin doubler and frame stiffener specified in Boeing Service

Bulletin 747-54-2901, Revision 5, dated April 26, 1990, in

accordance with that service bulletin; or in accordance with a

method approved by the Manager, Seattle Aircraft Certification

Office (ACO), FAA, Transport Airplane Directorate. Thereafter,

repeat that inspection at intervals not to exceed 15 months.

(f) Installation of a frame stiffener and a skin doubler

referred to in Boeing Service Bulletin 747-54-2091 as ``terminating

action'' does not constitute terminating action for the inspection

requirements 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 3: 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

Secs. 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 June 8, 1994.

Darrell M. Pederson,

Acting Manager, Transport Airplane Directorate, Aircraft Certification

Service.

[FR Doc. 94-14362 Filed 6-13-94; 8:45 am]

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