AD 95-23-06 ACTIVE

This amendment adopts a new airworthiness directive (AD) that is applicable to certain British Aerospace Model BAe 146-100A, -200A, and -300A airplanes and Model Avro 146-RJ70A, -RJ85A, and RJ-100A airplanes. This action requires inspections to detect cracking and evidence of exhaust leaks in the forward face of the central panel of the forward firewall of the auxiliary power unit (APU) bay, and replacement of the central panel with a new panel, if necessary. This amendment is prompted by a report indicating that cracking due to leakage of hot exhaust gases was found in the forward face of the forward firewall of the APU bay. The actions specified in this AD are intended to prevent such gas leakage and subsequent cracking, which could damage the wiring to the APU fire bottle; this condition could result in failure of the APU fire bottle to discharge in the event of an APU fire.

Final rule; request for comments

95-23-06 BRITISH AEROSPACE REGIONAL AIRCRAFT LIMITED, AVRO INTERNATIONAL AEROSPACE DIVISION (Formerly British Aerospace, plc; British Aerospace Commercial Aircraft Limited): Amendment 39-9426. Docket 95-NM-206-AD.
Applicability: Model BAe 146-100A, -200A, and -300A airplanes, and Model Avro 146-RJ70A, -RJ85A, and RJ-100A airplanes; on which British Aerospace Modification HCM36019A is installed; certificated in any category.

NOTE 1: This AD applies to each airplane identified in the preceding applicability provision, regardless of whether it has been otherwise 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 (d) of this AD to request approval from the FAA. This approval may address either no action, if the current configuration eliminates the unsafecondition; 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 leakage of hot exhaust gases and subsequent cracking of the forward face of the forward firewall of the auxiliary power unit (APU) bay, which could damage the wiring to the APU fire bottle and result in failure of the APU fire bottle to discharge in the event of an APU fire, accomplish the following:

(a) Within 7 days after the effective date of this AD: Perform a close detailed visual inspection to detect cracking and evidence of exhaust leaks in the forward face of the central panel of the forward firewall of the APU bay, in accordance with British Aerospace Service Bulletin S.B.26-35, Revision 1, dated August 30, 1995.

NOTE 2: Inspections accomplished prior to the effective date of this AD in accordance with British Aerospace Service Bulletin S.B.26-35, dated May 17, 1995, are considered acceptable for compliance with the applicable action specified in this amendment.

(1) If no crack or evidence of gas leakage is found, repeat the inspection required by paragraph (a) of this AD thereafter at intervals not to exceed 200 landings, except as provided by paragraph (b) of this AD.

(2) If any crack is found, but no evidence of gas leakage is detected, repeat the inspection required by paragraph (a) of this AD thereafter at daily intervals. Within 14 days after detecting any crack, accomplish the replacement specified in paragraph (c) of this AD.

(3) If any crack is found and evidence of gas leakage is detected, prior to further flight, accomplish the replacement specified in paragraph (c) of thisAD. Operation of the APU is prohibited (either when the aircraft is on the ground or in flight) until the replacement is accomplished.

(b) Installation of a protective aluminum alloy shield on the vertical stiffener (left-hand) next to the exhaust aperture of the forward firewall of the APU bay (Modification HCM36179B), in accordance with British Aerospace Service Bulletin SB.26-36-36179B, dated June 22, 1995, increases the interval for repetitive inspections required by paragraph (a)(1) of this AD from 200 landings to 400 landings.

(c) Replacement of the central panel of the forward firewall of the APU bay with a new panel (Modification HCM36179A), in accordance with British Aerospace Service Bulletin SB.26-35-36179A, dated August 4, 1995, constitutes terminating action for the requirements of this AD.

(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, Standardization Branch, ANM-113, 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, Standardization Branch, ANM-113.

NOTE 3: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Standardization Branch, ANM-113.

(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 actions shall be done in accordance with British Aerospace Service Bulletin S.B.26-35, Revision 1, dated August 30, 1995; British Aerospace Service Bulletin SB.26-35-36179A, dated August 4, 1995; and British Aerospace Service Bulletin SB.26-36-36179B, dated June 22, 1995. 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 British Aerospace Holding, Inc., Avro International Aerospace Division, P.O. Box 16039, Dulles International Airport, Washington DC 20041-6039. 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 November 29, 1995.

The Civil Aviation Authority (CAA), which is the airworthiness authority for the United Kingdom, recently notified the FAA that an unsafe condition may exist on certain British Aerospace Model BAe 146-100A, -200A, and -300A airplanes and Model Avro 146-RJ70A, -RJ85A, and RJ-100A airplanes. The CAA advises that it received a report indicating that cracking was found in the aluminum face plate on the forward side of the central panel of the forward firewall of the auxiliary power unit (APU) bay on a British Aerospace Model BAe 146 series airplane. Hot exhaust gases escaped through the sealing system used around the duct at the central panel of the forward firewall of the APU bay. Exposure to these hot gases resulted in cracking of the aluminum alloy portion of the central panel. Leakage of additional hot gases through the seal and resultant cracking could damage the wiring to the APU fire bottle. This condition, if not corrected, could result in failure of the APU fire bottle to discharge in the event of an APU fire.

British Aerospace has issued Service Bulletin S.B.26-35, Revision 1, dated August 30, 1995, which describes procedures for repetitive close detailed visual inspections to detect cracking and evidence of exhaust leaks in the forward face of the central panel of the forward firewall of the APU bay. For airplanes on which both cracking and evidence of gas leakage are found, the service bulletin specifies that operation of the APU must be prohibited either when the aircraft is on the ground or in flight until the central panel has been replaced with a new panel. The CAA classified this service bulletin as mandatory in order to assure the continued airworthiness of these airplanes in the United Kingdom.

British Aerospace also has issued Service Bulletin SB.26-35-36179A, dated August 4, 1995, which describes procedures for replacement of the central panel (constructed of aluminum alloy) of the forward firewall of the APU bay with a new panel constructed of titanium TA2 (Modification HCM36179A). The modification also involves replacing the associated stiffeners. The titanium central panel will provide better resistance to cracking at high temperatures. Accomplishment of this modification eliminates the need for repetitive inspections of the forward face of the central panel of the forward firewall of the APU bay.

For airplanes on which the previously described modification has not been accomplished, British Aerospace also has issued Service Bulletin SB.26-36-36179B, dated June 22, 1995, which describes procedures for installation of a protective aluminum alloy shield on the vertical stiffener (left-hand) next to the exhaust aperture of the forward firewall of the APU bay (Modification HCM36179B). Accomplishment of the installation provides protection of the wiring installation of the APU fire bottle. The service bulletin specifies that accomplishment of this installation increases the interval for repetitive inspections of the forward face of the central panel of the forward firewall of the APU bay to coincide with regularly scheduled maintenance of the affected airplanes.

These airplane models are manufactured in the United Kingdom and are type certificated for operation in the United States under the provisions of section 21.29 of the Federal Aviation Regulations (14 CFR 21.29) and the applicable bilateral airworthiness agreement. Pursuant to this bilateral airworthiness agreement, the CAA has kept the FAA informed of the situation described above. The FAA has examined the findings of the CAA, reviewed all available information, and determined that AD action is necessary for products of this type design that are certificated for operation in the United States.

Since an unsafe condition has been identified that is likely to exist or develop on other airplanes of the same type design registered in the United States, this AD is being issued to prevent leakage ofhot exhaust gases and subsequent cracking of the forward face of the forward firewall of the APU bay, which could damage the wiring to the APU fire bottle and result in failure of the APU fire bottle to discharge in the event of an APU fire. This AD requires repetitive close detailed visual inspections to detect cracking and evidence of exhaust leaks in the forward face of the central panel of the forward firewall of the APU bay, and replacement of the central panel with a new panel, if necessary. Such replacement, if accomplished, constitutes terminating action for the requirements of this AD. For airplanes on which cracking and evidence of gas leakage are found, this AD also prohibits operation of the APU (either when the aircraft is on the ground or in flight) until the central panel has been replaced with a new panel. This AD also provides for installation of a protective aluminum alloy shield on the vertical stiffener (left-hand) next to the exhaust aperture of the forward firewall of the APU bay, which, if accomplished, increases the interval for repetitive inspections of the forward face of the central panel of the forward firewall of the APU bay. The actions are required to be accomplished in accordance with the service bulletins described previously.

Operators should note that, for airplanes on which cracks are found, but no evidence of gas leakage is found, British Aerospace Service Bulletin S.B.26-35 recommends that daily inspections be accomplished and that corrective action be accomplished at the "next convenient downtime." This AD, however, requires daily inspections and accomplishment of the corrective action (replacement of the central panel) within 14 days after crack detection. The FAA finds that a 14-day compliance time will address the unsafe condition in a timely manner and will decrease reliance on daily inspections, which require approximately one work hour to perform.

Since a situation exists that requires the immediate adoption of this regulation, it is found that notice and opportunity for prior public comment hereon are impracticable, and that good cause exists for making this amendment effective in less than 30 days.

Comments Invited

Although this action is in the form of a final rule that involves requirements affecting flight safety and, thus, was not preceded by notice and an opportunity for public comment, comments are invited on this rule. Interested persons are invited to comment on this 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 under the caption "ADDRESSES." All communications received on or before the closing date for comments will be considered, and this rule may be amended in light of the comments received. Factual information that supports the commenter's ideas and suggestions is extremely helpful in evaluating the effectiveness of the ADaction and determining whether additional rulemaking action would be needed.

Comments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the rule that might suggest a need to modify the 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 that summarizes each FAA-public contact concerned with the substance of this AD will be filed in the Rules Docket.

Commenters wishing the FAA to acknowledge receipt of their comments submitted in response to this rule must submit a self-addressed, stamped postcard on which the following statement is made: "Comments to Docket Number 95-NM-206-AD." The postcard will be date stamped and returned to the commenter.

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.

The FAA has determined that this regulation is an emergency regulation that must be issued immediately to correct an unsafe condition in aircraft, and that it is not a "significant regulatory action" under Executive Order 12866. It has been determined further that this action involves an emergency regulation under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979). If it is determined that this emergency regulation otherwise would be significant under DOT Regulatory Policies and Procedures, a final regulatory evaluation will be prepared and placed in the Rules Docket. A copy of it, if filed, 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 USC 106(g), 40101, 40113, 44701.

39.13 - [Amended]
2. Section 39.13 is amended by adding the following new airworthiness directive:

Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-103, Attention: Rules Docket No. 95-NM-206-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056. The service information referenced in this AD may be obtained from British Aerospace Holding, Inc., Avro International Aerospace Division, P.O. Box 16039, Dulles International Airport, Washington DC 20041-6039. This information may be examined 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.

Tim Backman, Aerospace Engineer, Standardization Branch, ANM-113, FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (206) 227-2797; fax (206) 227-1149.