[Federal Register Volume 59, Number 235 (Thursday, December 8, 1994)]
[Unknown Section]
[Page 0]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 94-30142]


[[Page Unknown]]

[Federal Register: December 8, 1994]


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DEPARTMENT OF TRANSPORTATION
14 CFR Part 39

[Docket No. 94-NM-158-AD]

 

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

AGENCY: Federal Aviation Administration, DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: This document proposes the adoption of a new airworthiness 
directive (AD) that is applicable to certain Boeing Model 737-300, -
400, and -500 series airplanes. This proposal would require the 
application of an improved topcoat material to the insulation of the 
inner wall of the fan duct cowl (the firewall) of the thrust reversers. 
This proposal 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 the proposed AD 
are intended to prevent failure of the fireproof insulation topcoat 
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: Comments must be received by February 6, 1995.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-103, 
Attention: Rules Docket No. 94-NM-158-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: 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:

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-158-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-158-AD, 1601 Lind Avenue, SW., Renton, Washington 
98055-4056.

Discussion

    The topcoat material used on the firewall insulation of the thrust 
reverser fan duct cowls installed on Boeing Model 737 series airplanes 
equipped with CFM 56-3 series engines was changed in 1991 to decrease 
weight. (This change was considered to be a product improvement.) At 
that time, Dow Corning DC92-010 topcoat material was approved as an 
optional fireproof topcoat, that could be used in lieu of the 
previously used RTV60 topcoat material, for use on MA-25S and Crown-
Metro 64-C1-2 insulation located on the inner surface of the firewall 
panel. The qualification testing of Dow Corning DC92-010 topcoat 
material included fire tests of panels on which this material had been 
applied on insulation other than MA-25S and Crown-Metro 64-C1-2 
insulation materials.
    In November 1991, Boeing began using Dow Corning DC92-010 topcoat 
material on the insulation of the fan duct inner wall and upper 
bifurcation of the thrust reverser fan duct cowls installed on Model 
737-300, -400, and -500 series airplanes equipped with CFM 56-3 series 
engines. Subsequent burner rig development testing, however, indicated 
that this change to Dow Corning DC92-010 topcoat material had adversely 
affected the performance of the firewall panels that were insulated 
with MA-25S and Crown Metro 64-C1-2 insulation materials. The test 
panels that were insulated with MA-25S material and those insulated 
with Crown Metro 64-C1-2 successfully withstood a 2000 degrees 
Fahrenheit flame for 15 minutes with backside airflow, as is required 
by part 25 of the Federal Aviation Regulations (FAR) (14 CFR part 25). 
However, during static testing of the panels, which is also required by 
the part 25 of the FAR, flame penetrated the panels insulated with MA-
25S at approximately 5 minutes into the test, due to mud cracking and 
fissuring of the insulation. The panels insulated with Crown Metro 64-
C1-2 material passed this static fire test.
    Failure of the fireproof insulation topcoat installed on the 
firewalls for the thrust reverser fan cowls can result in degradation 
or loss of the firewall, which could lead to an uncontained engine 
fire.
    In light of the results of this testing, and in order to ensure the 
integrity of the engine cowl firewall on the affected Model 737 series 
airplanes, Boeing discontinued using Dow Corning DC92-010 topcoat 
material on airplanes in production as of February 1992. The RTV60 
topcoat material has been used on airplanes produced as of that date.
    Additionally, Boeing developed a repair configuration for those 
Model 737's that were delivered with the Dow Corning DC92-010 topcoat 
material. This repair consists of the application of a improved topcoat 
material on the existing surface.
    The FAA has reviewed and approved Boeing Alert Service Bulletin 
737-78A1056, dated August 11, 1994, which describes procedures for 
applying an improved fireproof topcoat on the fire wall of the thrust 
reverser fan duct cowls. The topcoat is comprised of a layer of Nextel 
fabric embedded in another layer of Dow Corning DC92-010, which is 
applied over the existing surface.
    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 require application of an improved fireproof topcoat 
on the fire wall of the thrust reverser fan duct cowls. The actions 
would be required to be accomplished in accordance with the service 
bulletin described previously.
    This proposed rule would be applicable only to airplanes having 
line numbers 2137 through 2271, inclusive. Beginning with line number 
2272, Dow Corning DC92-010 topcoat material was no longer used as a 
topcoat on the insulation of the subject firewalls.
    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 would be affected by this 
proposed AD, that it would take approximately 13 work hours per 
airplane to accomplish the proposed actions, and that the average labor 
rate is $60 per work hour. Required parts would be provided by the 
manufacturer at no charge to the operators. Based on these figures, the 
total cost impact of the proposed 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 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 adding the following new 
airworthiness directive:

Boeing: 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 24 months after the effective date of this AD, 
inspect the inner wall of the 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 a 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 
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 December 2, 1994.
James V. Devany,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 94-30142 Filed 12-7-94; 8:45 am]
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