AD 96-23-08

This amendment adopts a new airworthiness directive (AD), applicable to certain British Aerospace Model BAe 146 and Model Avro 146-RJ series airplanes, that requires repetitive tests of the integrity of the electrical circuit between the windshear computer and the flap position sensor, and repair of the electrical wiring, if necessary. This amendment also requires replacement of certain windshear computers with new computers, which, when accomplished, terminates the repetitive tests. This amendment is prompted by a report indicating that the existing windshear computer is not capable of detecting a signal indicating loss of flap position; this could result in the flightcrew following erroneous computer-generated guidance. The actions specified by this AD are intended to prevent the incapability of the windshear computer to detect the true flap position, which, if not corrected, could result in the inability of the flightcrew to avoid a windshear encounter, and consequent reduced controllability of the airplane.

Final rule

96-23-08 BRITISH AEROSPACE: Amendment 39-9813. Docket 96-NM-40-AD.
Applicability: Model BAe 146 and Model Avro 146-RJ series airplanes on which BAe Modification HCM40270A or HCM40270B (Safe Flight Windshear Computer) has been 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 request approval for an alternative method of compliance in accordance with paragraph (e) of this AD. The request should include an assessment of the effect of the modification, alteration, or repair on the unsafe condition addressed by this AD; and, if the unsafe condition has not been eliminated, the request should include specific proposedactions to address it.

Compliance: Required as indicated, unless accomplished previously.

To prevent the inability of the flightcrew to avoid a windshear encounter and consequent reduced controllability of the airplane due to the inability of the windshear computer to detect the true flap position, accomplish the following:

(a) Within 300 landings or 60 days after the effective date of this AD, whichever occurs first: Perform a test of the integrity of the electrical circuit between the windshear computer and the flap position sensor, in accordance with Avro International Aerospace Alert Inspection Service Bulletin S.B. 34-A155, Revision 2, dated August 9, 1995. Repeat the test thereafter at intervals not to exceed 300 landings until the actions required by paragraph (c) of this AD are accomplished.

(b) If any test required by paragraph (a) of this AD fails, prior to further flight, repair the electrical wiring in accordance with Avro International Aerospace Alert Inspection Service Bulletin S.B. 34-A155, Revision 2, dated August 9, 1995. Thereafter, repeat the test required by paragraph (a) of this AD at intervals not to exceed 300 landings until the actions required by paragraph (c) of this AD are accomplished.

(c) Within 6 months after the effective date of this AD: Replace any Safe Flight windshear computer having part number 6508-2 or 6508-4 with a new Safe Flight windshear computer having part number 6508-5; and change the polarity of the polarizing keys; in accordance with British Aerospace Modification Service Bulletin SB.34-160-70548A, dated November 21, 1994. Accomplishment of these actions constitutes terminating action for the repetitive tests required by paragraph (a) of this AD.

(d) As of the effective date of this AD, no person shall install a Safe Flight windshear computer having part number 6508-2 or 6508-4 on any airplane.

(e) 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 2: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Standardization Branch, ANM-113.

(f) 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.

(g) The actions shall be done in accordance with Avro International Aerospace Alert Inspection Service Bulletin S.B. 34-A155, Revision 2, dated August 9, 1995; or British Aerospace Modification Service Bulletin SB.34-160-70548A, dated November 21, 1994; as applicable. Avro International Aerospace Alert Inspection Service Bulletin S.B.34-A155, Revision 2, dated August 9, 1995, contains the following list of specified effective pages:

Page Number
Revision Level
Shown on Page
Date
Shown on Page
1, 2
2
August 9, 1995
3-5
1
September 10, 1993

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 Regional Aircraft Limited, Avro International Aerospace Division, Customer Support, Woodford Aerodrome, Woodford, Cheshire SK7 1QR, England. 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.

(h) This amendment becomes effective on December 19, 1996.

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 British Aerospace Model BAe 146 and Model Avro 146-RJ series airplanes was published in the Federal Register on August 26, 1996 (61 FR 43692). That action proposed to require repetitive tests of the integrity of the electrical circuit between the windshear computer and the flap position sensor, and repair of the electrical wiring, if necessary. That action also proposed to require replacement of existing windshear computers with new safe flight windshear computers.

Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the single comment received.

The commenter supports the proposed rule.

Conclusion
After careful review of the available data, including the comment noted above, the FAA has determined that air safety and the public interest require the adoption of the rule as proposed.

Cost Impact
The FAA estimates that 41 British Aerospace Model BAe 146 series airplanes and Model Avro 146-RJ series airplanes of U.S. registry will be affected by this AD, that it will take approximately 1 work hour per airplane to accomplish the required actions, and that the average labor rate is $60 per work hour. Based on these figures, the cost impact of the AD on U.S. operators is estimated to be $2,460, or $60 per airplane, per test cycle.

The FAA estimates that it will take approximately 4 work hours per airplane to accomplish the proposed replacement, at an average labor rate of $60 per work hour. Required parts will be supplied by the manufacturer at no cost to operators. Based on these figures, the cost impact of the replacement on U.S. operators is estimated to be $9,840, or $240 per airplane.

The cost impact figures discussed above are based on assumptions that no operator has yetaccomplished 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.

Regulatory Impact
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. 106(g), 40113, 44701.

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