[Federal Register Volume 59, Number 113 (Tuesday, June 14, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-14362]


[[Page Unknown]]

[Federal Register: June 14, 1994]


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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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