[Federal Register Volume 63, Number 226 (Tuesday, November 24, 1998)]
[Proposed Rules]
[Pages 64915-64918]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 98-31326]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 98-NM-76-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 747 Series Airplanes

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 747 series 
airplanes, that currently requires a one-time inspection to detect 
cracking and corrosion of various areas at all four nacelle struts; and 
repair, if necessary. This action would require new repetitive 
inspections to detect fatigue cracking or loose or missing fasteners of 
the aft torque bulkheads of the outboard nacelle struts; and repair, if 
necessary. In addition, this action would expand the applicability of 
the existing AD to include additional airplanes. This proposal is 
prompted by the availability of new service instructions for detecting 
fatigue cracking that would not have been detected by the required 
actions of the existing AD. The actions specified by the proposed AD 
are intended to detect and correct such fatigue cracking

[[Page 64916]]

and loose or missing fasteners, which could result in failure of an 
outboard nacelle strut, and consequent separation of the nacelle from 
the wing.

DATES: Comments must be received by January 8, 1999.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-114, 
Attention: Rules Docket No. 98-NM-76-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: Tamara L. Anderson, Aerospace 
Engineer, Airframe Branch, ANM-120S, FAA, Transport Airplane 
Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue, 
SW., Renton, Washington 98055-4056; telephone (425) 227-2771; fax (425) 
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 98-NM-76-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-114, Attention: Rules 
Docket No. 98-NM-76-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    On December 31, 1996, the FAA issued AD 96-26-51, amendment 39-9876 
(62 FR 1038, January 8, 1997), applicable to certain Boeing 747 series 
airplanes, to require a one-time detailed visual inspection to detect 
cracking and corrosion of various areas at all four nacelle struts; and 
repair, if necessary. That action was prompted by reports of cracking 
of the aft torque bulkhead at the inboard and outboard nacelle struts. 
That action was applicable only to Model 747 series airplanes that were 
equipped with Rolls-Royce-type engines. The requirements of that AD 
were intended to detect and correct cracking of an inboard or outboard 
nacelle strut, which could result in failure of the nacelle strut and 
consequent separation of the nacelle from the wing.

Actions Since Issuance of Previous Rule

    Since the issuance of that AD, the FAA has learned that the 
original report of fatigue cracking on the inboard strut was made in 
error. In fact, what was at first thought to be a fatigue crack on the 
inboard strut was later determined to be merely a surface scratch in 
the finish of the structure. Furthermore, the FAA has determined from 
the service history of the Model 747 airplane that only the outboard 
strut has proved to be susceptible to fatigue cracking of the aft 
torque bulkhead. Investigation has revealed that this is because the 
applied loading spectrum and design configuration of the outboard strut 
are significantly different from those of the inboard strut.
    In addition, since the issuance of AD 96-26-51, the FAA has 
received an additional report of fatigue cracking found on another 
Model 747 airplane, which also was equipped with Rolls-Royce-type 
engines. The affected airplane had accumulated 18,663 total flight 
cycles. That airplane was found to have cracking on both the inboard 
and outboard vertical chords of the aft torque bulkhead on the number 4 
nacelle strut. Specifically, two cracks of 0.53 inch and 0.34 inch in 
length were found on the inboard vertical chord of the aft torque 
bulkhead; and a single 0.12-inch crack was found on the outboard 
vertical chord of the aft torque bulkhead.
    In addition, whereas the strut design configurations and applied 
loading spectra are significantly different for the inboard and 
outboard struts, analysis shows that this is not the case for many of 
the different engine types that can be installed on the outboard strut. 
Therefore, outboard struts equipped with Rolls-Royce Model RB211, 
General Electric Model CF6-45/50, or Pratt & Whitney Model JT9D-70 
series engines also may be susceptible to fatigue cracking.
    Also, the FAA has received reports of nine other nacelle struts 
that were found to have loose fasteners at the attachment between the 
vertical flange of the lower spar fitting and the aft torque bulkhead; 
there have been no reports of missing fasteners at this location. The 
cause of the fasteners becoming loose is not yet known.
    These conditions (namely, fatigue cracking of the outboard nacelle 
strut aft torque bulkhead web, vertical chords, and side skin; or loose 
fasteners where the lower spar fitting attaches to the aft torque 
bulkhead), if not corrected, could result in failure of an outboard 
nacelle strut, and consequent separation of the nacelle from the wing.

Explanation of Relevant Service Information

    The FAA has reviewed and approved Boeing Alert Service Bulletin 
747-54A2184, dated July 3, 1997. The alert service bulletin describes 
procedures for repetitive detailed visual inspections to detect fatigue 
cracking of the web, vertical chords, and nacelle strut side skin of 
the aft torque bulkheads of the number 1 and 4 nacelle struts; and 
repair, if necessary. The repetitive inspections will also detect loose 
or missing fasteners on the lower spar fitting of the aft torque 
bulkhead. In addition, the alert service bulletin describes procedures 
for various repetitive non-destructive test (NDT) inspections to detect 
fatigue cracking of the aft torque bulkhead of the numbers 1 and 4 
nacelle struts; and repair, if necessary. The NDT inspections consist 
of ultrasonic inspections, surface eddy current inspections, and open-
hole eddy current inspections. The type of NDT inspection to be done 
depends upon the type of nacelle strut on the affected airplane. 
Accomplishment of the actions specified in the alert service bulletin 
is intended to adequately address the identified unsafe condition.

[[Page 64917]]

Explanation of Requirements of Proposed Rule

    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 all requirements of AD 96-26-51. This 
proposed AD would require repetitive detailed visual inspections and, 
for certain engine types, NDT inspections, to detect fatigue cracking 
or loose or missing fasteners of the aft torque bulkheads of the 
outboard nacelle struts; and repair, if necessary. This proposed AD 
also would revise the applicability of the existing AD to include 
additional airplanes having engine types in addition to those specified 
in the existing AD.
    This proposed AD also provides for an optional terminating action 
for the repetitive inspections proposed for airplanes equipped with 
General Electric CF6-45/50 or Pratt & Whitney JT9D-70 nacelle struts. 
[This same terminating action, although optional for this proposed AD, 
is required by another AD, namely, AD 95-13-07, amendment 39-9287 (60 
FR 33336, June 28, 1995), as discussed below]. The FAA notes that there 
is, as yet, no terminating action for those airplanes equipped with 
Rolls-Royce RB-211 nacelle struts.
    The actions above would be required to be accomplished in 
accordance with the alert service bulletin described previously, except 
as discussed below.

Differences Between Proposed Rule and Alert Service Bulletin

    Operators should note that, although the alert service bulletin 
provides for certain repair actions and specifies that the manufacturer 
may be contacted for disposition of other repair conditions, this 
proposal would require the repair of all conditions to be accomplished 
in accordance with a method approved by the FAA, or in accordance with 
data meeting the type certification basis of the airplane approved by a 
Boeing Company designated engineering representative who has been 
authorized by the FAA to make such findings.
    In addition, operators should note that there is a typographical 
error on Sheet 3 of Figure 1 of the alert service bulletin. The logic 
block that contains a reference to ``Group 1 airplanes'' should have 
read ``Groups 1 and 2 airplanes.''

Other Relevant Rulemaking

    The FAA has previously issued AD 95-13-07, which requires 
modification of airplanes equipped with General Electric CF6-45/50 or 
Pratt & Whitney JT9D-70 nacelle struts. Accomplishment of the 
modification required by that AD constitutes terminating action for the 
requirements of this proposed AD. However, this proposed AD would not 
affect the current requirements of AD 95-13-07.

Cost Impact

    There are approximately 273 airplanes of the affected design in the 
worldwide fleet. The FAA estimates that 24 airplanes of U.S. registry 
would be affected by this proposed AD.
    The new inspections that are proposed in this AD action for 
airplane Groups 3 and 4 would take approximately 24 work hours per 
airplane to accomplish, at an average labor rate of $60 per work hour. 
Based on these figures, the cost impact of the proposed requirements of 
this AD on U.S. operators of airplanes in Groups 3 and 4 is estimated 
to be $34,560, or $1,440 per airplane, per inspection cycle.
    The cost impact figure discussed above is based on assumptions that 
no operator has yet accomplished any of the current or proposed 
requirements of this AD action, and that no operator would accomplish 
those actions in the future if this AD were not adopted.
    There currently are no affected airplanes on the U.S. Register 
identified as Group 1 or 2 in the referenced alert service bulletin. 
The airplanes included in Groups 1 and 2 of the applicability of this 
rule currently are operated by non-U.S. operators under foreign 
registry; therefore, they are not directly affected by this AD action. 
However, the FAA considers that this rule is necessary to ensure that 
the unsafe condition is addressed in the event that any of these 
subject airplanes are imported and placed on the U.S. Register in the 
future.
    Should an affected Group 1 or 2 airplane be imported and placed on 
the U.S. Register in the future, it would require approximately 78 work 
hours to accomplish the new inspections proposed in this AD, at an 
average labor rate of $60 per work hour. Based on these figures, the 
cost impact of this proposed AD on airplane Groups 1 and 2 would be 
$4,680 per airplane, per inspection cycle.

Regulatory Impact

    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. 106(g), 40113, 44701.

Sec. 39.13  [Amended]

    2. Section 39.13 is amended by removing amendment 39-9876 (62 FR 
1038, January 8, 1997), and by adding a new airworthiness directive 
(AD), to read as follows:

Boeing: Docket 98-NM-76-AD. Supersedes AD 96-26-51, Amendment 39-
9876.

    Applicability: Model 747 series airplanes, as listed in Boeing 
Alert Service Bulletin 747-54A2184, dated July 3, 1997, certificated 
in any category:

    Note 1: This AD applies to each airplane identified in the 
preceding applicability provision, regardless of whether it has been 
modified, altered, or repaired in the area subject to the 
requirements of this AD. For airplanes that have been modified, 
altered, or repaired so that the performance of the requirements of 
this AD is affected, the owner/operator must request approval for an 
alternative method of compliance in accordance with paragraph (e) of 
this AD. The request should include an assessment of the effect of 
the modification, alteration, or repair on the unsafe condition 
addressed by this AD; and, if the unsafe condition has not been 
eliminated, the request should include specific proposed actions to 
address it.

    Compliance: Required as indicated, unless accomplished 
previously.

[[Page 64918]]

    To detect and correct fatigue cracking and loose or missing 
fasteners of the aft torque bulkheads of the outboard nacelle 
struts, which could result in failure of an outboard nacelle strut, 
and consequent separation of the nacelle from the wing, accomplish 
the following:
    (a) For airplanes identified as Groups 1 and 2 airplanes in 
Boeing Alert Service Bulletin 747-54A2184, dated July 3, 1997: Prior 
to the accumulation of 12,000 total flight cycles, or within 90 days 
after the effective date of this AD, whichever occurs later, perform 
a detailed visual inspection of the aft torque bulkheads of the 
number 1 and number 4 nacelle struts to detect fatigue cracking and 
loose or missing fasteners. The inspection shall be accomplished in 
accordance with Part I of the Accomplishment Instructions of Boeing 
Alert Service Bulletin 747-54A2184, dated July 3, 1997.

    Note 2: There is a typographical error on Sheet 3 of Figure 1 of 
the alert service bulletin. The words ``Group 1 airplanes'' should 
read ``Groups 1 and 2 airplanes.''
    (1) If no cracking, and if no loose or missing fastener is 
found, repeat the inspection thereafter at the intervals specified 
in Figure 1 of the alert service bulletin.
    (2) If any cracking, or if any loose or missing fastener is 
found, prior to further flight, repair in accordance with Part III 
of the alert service bulletin. Repeat the inspection thereafter at 
the intervals specified in Figure 1 of the alert service bulletin. 
Where the service bulletin specifies that the manufacturer may be 
contacted for disposition of certain repair conditions, repair in 
accordance with a method approved by the Manager, Seattle Aircraft 
Certification Office (ACO), FAA, Transport Airplane Directorate; or 
in accordance with data meeting the type certification basis of the 
airplane approved by a Boeing Company designated engineering 
representative (DER) who has been authorized by the Manager, Seattle 
ACO, to make such findings.
    (b) For airplanes identified as Groups 1 and 2 airplanes in 
Boeing Alert Service Bulletin 747-54A2184, dated July 3, 1997: Prior 
to the accumulation of 12,000 total flight cycles, or within 90 days 
after the effective date of this AD, whichever occurs later, perform 
a non-destructive test (NDT) inspection of the aft torque bulkheads 
of the number 1 and number 4 nacelle struts to detect fatigue 
cracking. The NDT inspection shall be accomplished in accordance 
with Part II of the Accomplishment Instructions of Boeing Alert 
Service Bulletin 747-54A2184, dated July 3, 1997.

    Note 3: The alert service bulletin refers to a variety of NDT 
inspections, consisting of ultrasonic inspections, surface eddy 
current inspections, and open-hole eddy current inspections. The 
logic diagram in Figure 1 of the alert service bulletin states the 
conditions under which each of these inspections is to be performed.

    (1) If no cracking is found, repeat the inspection thereafter at 
the intervals specified in Figure 1 of the alert service bulletin.
    (2) If any cracking is found, prior to further flight, repair in 
accordance with Part III of the alert service bulletin. Repeat the 
inspection thereafter at the intervals specified in Figure 1 of the 
alert service bulletin. Where the service bulletin specifies that 
the manufacturer may be contacted for disposition of certain repair 
conditions, repair in accordance with a method approved by the 
Manager, Seattle ACO; or in accordance with data meeting the type 
certification basis of the airplane approved by a Boeing Company DER 
who has been authorized by the Manager, Seattle ACO, to make such 
findings.
    (c) For airplanes identified as Groups 3 and 4 airplanes in 
Boeing Alert Service Bulletin 747-54A2184, dated July 3, 1997: Prior 
to the accumulation of 12,000 total flight cycles, or within 90 days 
after the effective date of this AD, whichever occurs later, perform 
a detailed visual inspection of the aft torque bulkheads of the 
number 1 and number 4 nacelle struts to detect fatigue cracking and 
loose or missing fasteners. The inspection shall be accomplished in 
accordance with Part I of the Accomplishment Instructions of Boeing 
Alert Service Bulletin 747-54A2184, dated July 3, 1997.
    (1) If no cracking, and if no loose or missing fastener is 
found, repeat the inspection thereafter at the intervals specified 
in Figure 1 of the alert service bulletin, until the applicable 
requirements of paragraph (d) are accomplished.
    (2) If any cracking, or if any loose or missing fastener is 
found, prior to further flight, repair in accordance with Part III 
of the alert service bulletin. Where the alert service bulletin 
specifies that the manufacturer may be contacted for disposition of 
certain repair conditions, repair in accordance with a method 
approved by the Manager, Seattle ACO; or in accordance with data 
meeting the type certification basis of the airplane approved by a 
Boeing Company DER who has been authorized by the Manager, Seattle 
ACO, to make such findings.
    (d) For airplanes identified as Groups 3 and 4 airplanes in 
Boeing Alert Service Bulletin 747-54A2184, dated July 3, 1997: 
Accomplishment of the nacelle strut modifications required in AD 95-
13-07, amendment 39-9287 (applicable to airplanes equipped with 
either General Electric CF6-45/50 or Pratt & Whitney JT9D-70 nacelle 
struts), constitutes terminating action for the requirements of this 
AD.
    (e) 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 4: Information concerning the existence of approved 
alternative methods of compliance with this AD, if any, may be 
obtained from the Seattle ACO.

    (f) 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 November 18, 1998.
Darrell M. Pederson,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 98-31326 Filed 11-23-98; 8:45 am]
BILLING CODE 4910-13-U