AD 95-09-01

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AD Number:
95-09-01
Document Type:
AD Final Rules
Docket Number:
94-NM-158-AD
Subject Heading:
Airworthiness Directives; Boeing Model 737-300, -400, and -500 Series Airplanes
Subject:
Fan Duct Cowl
Status:
Current
Citation:
(Federal Register: April 26, 1995 (Volume 60, Number 80))
Citation Publish Date:
04/26/1995
Effective Date:
05/26/1995
Make:
The Boeing Company
Model:
737-300 Series | 737-400 Series | 737-500 Series
Product Type:
Aircraft
Product Subtype:
Large Airplane
Affected AD:
Superseded AD:
Affected By:
Superseded By:
Service/Office:
Office of Primary Responsibility:
CFR Part Reference:
Part 39 (60 FR 20394 NO. 80 4/26/95)
Comments:
AIRWORTHINESS DIRECTIVES FINAL RULES: 95-09-01
CITATION:   [Federal Register: April 26, 1995 (Volume 60, Number 80)]

PAGE NUMBER:   [Page 20394]

DOCKET NUMBER:   94-NM-158-AD

AMENDMENT:   39-9205

AD NUMBER:   95-09-01

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

ACTION:   Final rule

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) 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. § 39.13 - [Amended]

2. Section 39.13 is amended by adding the following new airworthiness directive:

REGULATORY TEXT:  
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 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.

(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.

FOOTER: