99-23-22 R1 TRANSPORT CATEGORY AIRPLANES: Amendment 39-11473. Docket 99-NM-328-AD. Revises AD 99-23-22, Amendment 39-11418. Issued December 10, 1999.

Applicability: Transport category airplanes, as listed below, certificated in any category, equipped with any Mode "C" transponder with single Gillham code altitude input, including, but not limited to, the transponder part numbers listed below. Whether a Mode "C" transponder has a single Gillham code altitude input may be determined by reviewing the transponder installation instructions.

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 request approval for an alternative method of compliance in accordance with paragraph (d) 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 proposed actions to address it.

Compliance: Required as indicated, unless accomplished previously.

To prevent false Traffic Alert Collision Avoidance System (TCAS II) advisories due to inaccurate airplane altitude reporting, which could result in the flightcrew deviating the airplane from its assigned flight path and a possible mid-air collision, accomplish the following:

(a) Within 90 days after November 29, 1999 (the effective date of AD 99-23-22, amendment 39-11418) perform the test procedures specified in paragraphs (a)(1) through (a)(9) of this AD to detect any discrepancies of the Mode "C" transponder(s), air data computer (ADC), or Gillham wiring connections, in accordance with the applicable ADC and Mode "C" transponder component maintenance manuals and airplane maintenance manual. Repeat the test procedures thereafter at intervals not to exceed 90 days.

(1) Connect an air data test set to the Captain’s (No. 1) Pitot/Static system.

(2) In the airplane flight deck, select Mode "C" transponder (1), or left Mode "C" transponder, depending on airplane flight deck configuration, and select ADC source (1).

(3) Select the air data test set to the following altitude reporting values:

1,000 feet;

4,100 feet;

15,700 feet; and

31,000 feet.

(4) For each selected altitude, verify that the Mode "C" altitude reporting is within tolerance (+/-125 feet), and record the altitude output as follows:

1,000 feet (+/-125 feet);

4,100 feet (+/-125 feet);

15,700 (+/-125 feet); and

31,000 feet (+/-125 feet).

(5) In the airplane flight deck, select ADC source (2) and repeat paragraphs (a)(3) and (a)(4) of this AD.

(6) In the airplane flight deck, select Mode "C" transponder (2), or the right Mode "C" transponder, depending on airplane flight deck configuration, select ADC source (1), and repeat paragraphs (a)(3) and (a)(4) of this AD.

(7) In the airplane flight deck, select ADC source (2) and repeat paragraphs (a)(3) and (a)(4) of this AD.

(8) Connect an air data test set to the Captain’s (No. 2) Pitot/Static system.

(9) Repeat paragraphs (a)(2) through (a)(7) of this AD.

NOTE 2: The tests required by paragraph (a) of this AD examine the three primary sources of inaccurate airplane altitude reporting. These three sources are: ADC’s, Mode "C" transponders, and the Gillham wiring connections between the ADC and Mode "C" transponder.

(b) Except as permitted by the Master Minimum Equipment List (MMEL): If any discrepancy is detected during any test required by paragraph (a) of this AD: Prior to further flight, repair in accordance with the applicable ADC and Mode "C" transponder component maintenance manual and airplane maintenance manual. If the repair information is not available in the applicable manual, except as permitted by the MMEL, prior to further flight, repair in accordance with a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate.

NOTE 3: The airplane may be operated in accordance with the provisions and limitations specified in the FAA-approved MMEL, provided that only one Mode "C" transponder on the airplane is inoperative.

(c) Within 20 days after accomplishing the initial and repetitive tests required by paragraph (a) of this AD, submit a report of the inspection and test results (both positive and negative findings) to: Peter Skaves, Aerospace Engineer, Airplane and Flight Crew Interface Branch, ANM-111, FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; fax (425) 227-1320. The test results must include the Mode "C" transponder(s) and ADC part number(s), and must specify if any discrepancies of the Gillham wiring connections were detected, and if corrective action was required. Information collection requirements contained in this regulation have been approved by the Office of Management and Budget (OMB) under the provisions of the Paperwork Reduction Act of 1980 (44 U.S.C. 3501 et seq.) and have been assigned OMB Control Number 2120-0056.

(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, Airplane and Flight Crew Interface Branch, ANM-111, FAA, Transport Airplane Directorate. Operators shall submit their requests through an appropriate FAA Principal Maintenance or Avionics Inspector, who may add comments and then send it to the Manager, ANM-111.

NOTE 4: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Manager, ANM-111.

(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 effective date of this amendment remains November 29, 1999.

FOR FURTHER INFORMATION CONTACT:

Peter Skaves, Aerospace Engineer, Airplane and Flight Crew Interface Branch, ANM-111, FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 227-2795; fax (425) 227-1320.