[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]
BILLING CODE 4910-13-U
