[Federal Register Volume 59, Number 168 (Wednesday, August 31, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-20594]


[[Page Unknown]]

[Federal Register: August 31, 1994]


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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 94-NM-05-AD; Amendment 39-9012; AD 94-17-17]

 

Airworthiness Directives; Boeing Model 747 Series Airplanes 
Equipped With Pratt and Whitney JT9D-3 or JT9D-7 Series Engines, 
Excluding JT9D-70 Series Engines

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

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SUMMARY: This amendment adopts a new airworthiness directive (AD), 
applicable to certain Boeing Model 747 series airplanes, that requires 
inspections of the inboard and outboard strut chords, stiffeners, and 
web to detect cracks and loose fasteners; repair of the chords, 
stiffeners, or web, if necessary; and replacement of any loose 
fastener. This amendment is prompted by reports of fatigue cracks and 
loose fasteners found in the forward lower spar web of the inboard 
strut on Model 747 series airplanes equipped with Pratt & Whitney JT9D-
3 and JT9D-7 series engines. The actions specified by this AD are 
intended to prevent separation of the strut from the wing of the 
airplane due to fatigue cracking.

DATES: Effective September 30, 1994.
    The incorporation by reference of certain publications listed in 
the regulations is approved by the Director of the Federal Register as 
of September 30, 1994.

ADDRESSES: The service information referenced in this AD may be 
obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, 
Washington 98124-2207. This information may be examined at the Federal 
Aviation Administration (FAA), Transport Airplane Directorate, Rules 
Docket, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of 
the Federal Register, 800 North Capitol Street, NW., suite 700, 
Washington, DC.

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: A proposal to amend part 39 of the Federal 
Aviation Regulations (14 CFR part 39) to include an airworthiness 
directive (AD) that is applicable to certain Boeing Model 747 series 
airplanes was published in the Federal Register on March 17, 1994 (59 
FR 12560). That action proposed to require inspections of the inboard 
and outboard strut chords, stiffeners, and web to detect cracks and 
loose fasteners; repair of the chords, stiffeners, or web, if 
necessary; and replacement of any loose fastener.
    Interested persons have been afforded an opportunity to participate 
in the making of this amendment. Due consideration has been given to 
the comments received.
    One commenter supports the proposed rule.
    One commenter, Boeing, requests that the proposed rule be withdrawn 
since only six cracks have been reported in the 20 years these 
airplanes have been in service. In addition, these cracks were found 
only on the inboard struts during normal maintenance. Boeing asserts 
that the probability of another strut with a pre-existing firewall 
crack experiencing loads that approach the ultimate design condition is 
extremely remote. Boeing adds, however, that the airplane maintenance 
manual is being revised to include an inspection of the lower spar web 
in the case of an unusual overload event. Boeing also indicates that 
the results of one operator's inspections revealed only one loose 
fastener on one airplane out of 24 inspected. Boeing states that the 
firewall webs will be reinforced during the strut modification program 
referenced in the proposal.
    The FAA does not concur with the commenter's request to withdraw 
this AD. The FAA has determined that inspections mandated by the 
issuance of this AD are necessary to correct the unsafe condition 
presented by separation of the strut from the wing of the airplane due 
to fatigue cracking in the web. These inspections are necessary until 
the 0.025-inch inboard webs and the 0.032-inch outboard webs are 
replaced as part of the strut modification program discussed in the 
proposal. Sonic fatigue analysis performed by Boeing in support of the 
decision to replace the webs has revealed that the existing inboard and 
outboard webs on Model 747 series airplanes addressed in this AD are 
inadequate. Recent findings from an investigation of an incident 
involving a Model 747 series airplane indicate that fatigue cracking 
found on the web of the airplane resulted from flexing or vibration of 
the web material. This fatigue cracking resulted in the in-flight loss 
of an engine during airplane operation in severe turbulence. Since the 
FAA considers it probable for other airplanes to have cracked webs, and 
since no requirements exist to restrict airplane operation in severe 
turbulence, the FAA finds that this AD action is necessary in order to 
prevent in-flight engine loss.
    Several commenters request that inspections of the outboard webs be 
removed from the proposed rule so that the AD is consistent with the 
referenced service bulletin. The commenters indicate that no cracking 
or loose fasteners have been found on the outboard webs. The commenters 
also state that the design thickness of the webs (0.032 inch for the 
outboard web; 0.025 inch for the inboard web) represents a 28 percent 
difference, which should be considered significant.
    The FAA does not concur. The thickness of the inboard web of the 
incident airplane mentioned previously measured 0.027 inch. The FAA 
finds that there is little difference between the inboard and outboard 
webs with standard manufacturing tolerances. Each web is similar in 
configuration, loading, and sonic environments. In light of these 
considerations, the FAA concludes that the outboard strut web is 
subject to the same unsafe condition as the inboard strut web and must 
be included in this AD.
    Several commenters request that the compliance times for 
inspections of the outboard strut be extended. One commenter requests 
that the compliance times be revised to align with those recommended in 
the referenced service bulletin, less the amount of time provided for 
public comment on the proposal. Another commenter requests that the 
compliance times be extended to be consistent with a load analysis 
based upon the actual web thickness of the outboard strut. This 
commenter assumes that the proposed repetitive inspection interval is 
based on a load analysis of the inboard strut structure. Another 
commenter requests that the compliance times for the initial inspection 
of the inboard strut be extended to 15 months. The commenter does not 
provide any justification for this request, however.
    The FAA concurs that the compliance times can be extended somewhat. 
The compliance times specified in paragraphs (a)(1) and (a)(3) of this 
AD have been revised to reflect the times recommended in the 
manufacturer's service bulletin. The FAA finds that the proposed 
compliance time of 6 months specified for airplanes that have 
accumulated 6,000 or more total landings, but less than 15,000 total 
landings [those airplanes applicable to paragraph (a)(2) of the final 
rule] may be extended to 9 months. Although the service bulletin 
specifies a recommended compliance time of 12 months for those 
airplanes, the FAA finds that, based on the service history of affected 
Model 747 series airplanes that fall within this group, 9 months 
represents the maximum interval of time allowable for these airplanes 
to continue to operate without compromising safety.
    After careful review of the available data, including the comments 
noted above, the FAA has determined that air safety and the public 
interest require the adoption of the rule as proposed.
    This is considered to be interim action. The manufacturer has 
advised that it is currently developing a modification program for the 
engine strut that will positively address the unsafe condition 
addressed by this AD. Once this modification program is developed, 
approved, and available, the FAA may consider additional rulemaking.
    There are approximately 380 Model 747 series airplanes of the 
affected design in the worldwide fleet. The FAA estimates that 140 
airplanes of U.S. registry will be affected by this AD, that it will 
take approximately 22 work hours per airplane to accomplish the 
required actions, and that the average labor rate is $55 per work hour. 
Based on these figures, the total cost impact of the AD on U.S. 
operators is estimated to be $169,400, or $1,210 per airplane.
    The total cost impact figure discussed above is based on 
assumptions that no operator has yet accomplished any of the 
requirements of this AD action, and that no operator would accomplish 
those actions in the future if this AD were not adopted.
    The regulations adopted herein will 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 final 
rule does not have sufficient federalism implications to warrant the 
preparation of a Federalism Assessment.
    For the reasons discussed above, I certify that this action (1) is 
not a ``significant regulatory action'' under Executive Order 12866; 
(2) is not a ``significant rule'' under DOT Regulatory Policies and 
Procedures (44 FR 11034, February 26, 1979); and (3) 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 final evaluation has been prepared for this action 
and it is contained in the Rules Docket. A copy of it may be obtained 
from the Rules Docket at the location provided under the caption 
ADDRESSES.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Incorporation by 
reference, Safety.

Adoption of the Amendment

    Accordingly, pursuant to the authority delegated to me by the 
Administrator, the Federal Aviation Administration amends 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:

94-17-17 Boeing: Amendment 39-9012. Docket 94-NM-05-AD.

    Applicability: Model 747 series airplanes equipped with Pratt & 
Whitney JT9D-3 or JT9D-7 series engines, excluding JT9D-70 series 
engines; line numbers 001 through 510 inclusive; certificated in any 
category.
    Compliance: Required as indicated, unless accomplished 
previously.
    To prevent separation of the strut from the wing of the airplane 
due to fatigue cracking, accomplish the following:
    (a) Perform a detailed visual inspection of the inboard and 
outboard strut forward lower spar chords, stiffeners, and web to 
detect cracks and loose fasteners, in accordance with the procedures 
described in Boeing Service Bulletin 747-54-2160, dated September 9, 
1993, at the time specified in paragraph (a)(1), (a)(2), or (a)(3) 
of this AD, as applicable. Repeat this inspection thereafter at 
intervals not to exceed 2,000 landings or 8,000 hours time-in-
service, whichever occurs first.
    (1) For airplanes that have accumulated less than 6,000 total 
landings as of the effective date of this AD: Perform the initial 
inspection at the later of the times specified in paragraphs 
(a)(1)(i) and (a)(1)(ii) of this AD.
    (i) Prior to the accumulation of 6,000 total landings on the 
strut. Or
    (ii) Within 12 months after the effective date of this AD.
    (2) For airplanes that have accumulated 6,000 or more total 
landings, but less than 15,000 total landings, as of the effective 
date of this AD: Perform the initial inspection within 9 months 
after the effective date of this AD.
    (3) For airplanes that have accumulated 15,000 or more total 
landings as of the effective date of this AD: Perform the initial 
inspection within 6 months after the effective date of this AD.
    (b) If any crack is found during any inspection required by 
paragraph (a) of this AD, prior to further flight, repair in 
accordance with procedures specified in Chapter 54-10-03 of the 747 
Structural Repair Manual.
    (c) If any loose fastener is found during any inspection 
required by paragraph (a) of this AD, prior to further flight, 
replace the fastener in accordance with procedures specified in 
Chapter 51-30-02 of the 747 Structural Repair Manual.
    (d) 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.

    (e) 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.
    (f) The inspection shall be done in accordance with Boeing 
Service Bulletin 747-54-2160, dated September 9, 1993. This 
incorporation by reference was approved by the Director of the 
Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 
51. Copies may be obtained from Boeing Commercial Airplane Group, 
P.O. Box 3707, Seattle, Washington 98124-2207. Copies may be 
inspected at the FAA, Transport Airplane Directorate, 1601 Lind 
Avenue, SW., Renton, Washington; or at the Office of the Federal 
Register, 800 North Capitol Street, NW., suite 700, Washington, DC.
    (g) This amendment becomes effective on September 30, 1994.

    Issued in Renton, Washington, on August 17, 1994.
Darrell M. Pederson,
 Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 94-20594 Filed 8-30-94; 8:45 am]
BILLING CODE 4910-13-U