Airworthiness Directives; Boeing Model 737-300, -400, and -500 Series Airplanes

[Federal Register Volume 60, Number 80 (Wednesday, April 26, 1995)]
[Rules and Regulations]
[Pages 20394-20396]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 95-9771]



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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 94-NM-158-AD; Amendment 39-9205; AD 95-09-01]


Airworthiness Directives; Boeing Model 737-300, -400, and -500 
Series Airplanes

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 737-300, -400, and -500 series 
airplanes, that requires an inspection to determine the type of topcoat 
material currently on the insulation of the inner wall of the fan duct 
cowl (the firewall) of the thrust reversers, and application of an 
improved topcoat material, if necessary. This amendment is prompted by 
tests, which demonstrated that flames can penetrate the firewall if 
certain combinations of insulation and topcoat materials are used. The 
actions specified by this AD are intended to prevent failure of the 
fireproof insulation top coat installed on the firewalls of the thrust 
reverser fan cowls, which could result in degradation or loss of the 
firewall and lead to an uncontained engine fire.

DATES: Effective May 26, 1995.
    The incorporation by reference of certain publications listed in 
the regulations is approved by the Director of the Federal Register as 
of May 26, 1995.

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: Stephen Bray, Aerospace Engineer, 
Propulsion Branch, ANM-140S, Seattle Aircraft Certification Office, 
FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, 
Washington 98055-4056; telephone (206) 227-2681; 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) [[Page 20395]] that is applicable to certain Boeing 
Model 737-300, -400, and -500 series airplanes was published in the 
Federal Register on December 8, 1994 (59 FR 63277). That action 
proposed to require an inspection to determine the type of topcoat 
material currently on the insulation of the inner wall of the fan duct 
cowl (the firewall) of the thrust reversers, and application of an 
improved topcoat material, if necessary.
    Interested persons have been afforded an opportunity to participate 
in the making of this amendment. Due consideration has been given to 
the comments received.
    Several commenters request that the rule be revised so that, if the 
inspection reveals that the suspect topcoat material is present, 
operators would not be required to apply the improved topcoat material 
immediately prior to further flight. These commenters state that the 
application of the improved topcoat material should be permitted at the 
operator's convenience after a positive inspection finding. This would 
encourage operators to conduct the inspection promptly, and then allow 
them to schedule the time and materials necessary for accomplishing the 
topcoat application at their subsequent heavy maintenance check. One 
commenter contends that in-service experience has shown that the risk 
of an engine fire resulting from the problems associated with the 
topcoat material is very low; in light of this, it is appropriate to 
allow an extended interval of time between conducting the inspection 
and applying the improved top coat.
    The FAA does not concur with the request to permit application of 
the improved topcoat material at an extended interval after the 
inspection findings. It is the FAA's general policy that, once an 
unsafe condition has been determined to exist, that condition cannot be 
allowed to continue in the fleet. Therefore, it is essential that, if 
the inspection reveals that application of the improved topcoat is 
necessary, such application must be accomplished prior to further 
flight after the inspection.
    However, in light of the fact that there have been no in-service 
incidents associated with the addressed unsafe condition, and because 
the topcoat application procedures may be extensive for some operators, 
the FAA considers that the compliance time for the required actions can 
be extended somewhat. It is the FAA's intent that, if the application 
of the improved topcoat is necessary, it should be performed during a 
regularly scheduled maintenance interval when the airplane is at a base 
where special equipment, necessary parts, and trained personnel are 
available. If the compliance time for the action required by this AD is 
parallel to the operator's regular maintenance interval, the operator 
can easily schedule both the inspection and any necessary topcoat 
application to be performed during the same maintenance hold. In 
consideration of these factors, the FAA finds that the compliance time 
may be extended from the proposed 24 months to 30 months without 
compromising safety. This extension will allow the majority of affected 
operators to accomplish the required actions during scheduled 
maintenance visits.
    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 with the change previously 
described. The FAA has determined that this change will neither 
increase the economic burden on any operator nor increase the scope of 
the AD.
    There are approximately 135 Model 737-300, -400, and -500 series 
airplanes of the affected design in the worldwide fleet. The FAA 
estimates that 18 airplanes of U.S. registry will be affected by this 
AD, that it will take approximately 13 work hours per airplane to 
accomplish the required actions, and that the average labor rate is $60 
per work hour. Required parts will be provided by the manufacturer at 
no charge to the operators. Based on these figures, the total cost 
impact of the AD on U.S. operators is estimated to be $14,040, or $780 
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:

95-09-01  Boeing: Amendment 39-9205. Docket 94-NM-158-AD.

    Applicability: Model 737-300, -400, and -500 series airplanes; 
line numbers 2137 through 2271, inclusive; 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 use the authority 
provided in paragraph (b) to request approval from the FAA. This 
approval may address either no action, if the current configuration 
eliminates the unsafe condition; or different actions necessary to 
address the unsafe condition described in this AD. Such a request 
should include an assessment of the effect of the changed 
configuration on the unsafe condition addressed by this AD. In no 
case does the presence of any modification, alteration, or repair 
remove any airplane from the applicability of this AD.

    Compliance: Required as indicated, unless accomplished 
previously.
    To prevent the failure of the fireproof insulation topcoat 
installed on the firewalls for the thrust reverser fan cowls, which 
can result in degradation or loss of the firewall and lead to an 
uncontained engine fire, accomplish the following:
    (a) Within 30 months after the effective date of this AD, 
inspect the inner wall of the [[Page 20396]] fan duct cowl (the 
firewall) of the thrust reversers to determine the type of topcoat 
material installed, in accordance with Boeing Alert Service Bulletin 
737-78A1056, dated August 11, 1994.
    (1) If the existing topcoat has silica fibers in it, no further 
action is required by this AD.
    (2) If the existing topcoat does not have silica fibers in it, 
prior to further flight, accomplish the application of the DC92-010 
topcoat to the firewall of the thrust reversers in accordance with 
the service bulletin.
    (b) 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.

    (c) 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.
    (d) The inspection and application shall be done in accordance 
with Boeing Alert Service Bulletin 737-78A1056, dated August 11, 
1994. 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.
    (e) This amendment becomes effective on May 26, 1995.

    Issued in Renton, Washington, on April 14, 1995.
John J. Hickey,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 95-9771 Filed 4-25-95; 8:45 am]
BILLING CODE 4910-13-U

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