AD 99-23-22

This amendment adopts a new airworthiness directive (AD) that is applicable to various transport category airplanes equipped with certain Mode "C" transponder(s) with single Gillham code altitude input. This action requires repetitive tests to detect discrepancies of the Mode "C" transponder(s), air data computer, and certain wiring connections; and corrective actions, if necessary. This amendment is prompted by reports that, during level flight, the Traffic Alert Collision Avoidance System (TCAS II) issued false advisories that directed the flightcrew to change course and either climb or descend. The actions specified in this AD are intended to prevent such false 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.

Final rule; request for comments.

99-23-22 TRANSPORT CATEGORY AIRPLANES: Amendment 39-11418. Docket 99-NM-328-AD. Issued November 4, 1999.

Applicability: Transport category airplanes, 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. A Mode "C" transponder with single Gillham code altitude input is defined as any Mode "C" transponder meeting Aeronautical Radio, Inc. (ARINC) 572 specification.

Mode "C" Transponder Part Numbers:

Rockwell Collins
Bendix
Wilcox
IFF
622-2224-001
066-1056-00
97637-201
APX-100
622-2224-003
066-1056-01
97637-301
APX-101
522-2703-001
066-1123-00

522-2703-011
204-1599-6508

787-6211-001

787-6211-002

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 thisAD. 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:

Repetitive Tests
(a) Within 45 days after the effective date of this AD: Perform the test procedures specifiedin 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 45 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.

Corrective Actions
(b) 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, prior to further flight, repair in accordance with a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate.

Reporting Requirement
(c) Within 10 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.

Alternative Methods of Compliance
(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, Seattle ACO. 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, Seattle ACO.

NOTE 3: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Seattle ACO.

Special Flight Permits
(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) This amendment becomes effective on November 29, 1999.

The FAA has received reports of eleven incidents involving certain transport category airplanes equipped with Mode "C" transponder(s) with single Gillham code altitude input. These reports indicate that, during level flight, the TCAS II issued false advisories that directed the flightcrew to change course and either climb or descend. These instances all involved communication between airplanes with the TCAS II and airplanes having the Mode "C" transponder(s). The airplanes having the Mode "C" transponders are predominantly older, out-of-production transport category airplanes. In at least one instance, the Gillham wiring connection was determined to have failed, resulting in inaccurate altitude reporting by the Mode "C" transponder. There are three primary sources of failure that could lead to inaccurate airplane altitude reporting: the Mode "C" transponder(s), air data computer, and Gillham wiring connections. The exact cause of the failures is unknown at this time. Such inaccurate altitude reporting and consequent false TCAS II advisories, if not prevented, could result in the flightcrew deviating the airplane from its assigned flight path and a possible mid-air collision.

Additional Considerations
The FAA also has received information regarding inaccurate altitude reporting on airplanes equipped with TCAS II and Mode "S" transponders. Following one incident involving reduction of separation between two airplanes equipped with TCAS II and Mode "S" transponders, the Civil Aviation Authority (CAA), which is the airworthiness authority for the United Kingdom, issued British airworthiness directive 001-08-99. The British airworthiness directive applies to airplanes equipped with any Mode "S" transponder connected to a TCAS II system with Gillham altitude format, and requires repetitive tests of certain Mode "S" transponder systems to detect discrepancies, and corrective action, if necessary.

FAA's Determinations
Based on the numerous incidents involving airplanes equipped with TCAS II and Mode "C" transponders, the FAA considers that immediate action is required to address the unsafe condition identified previously. Since the exact cause of the failures leading to inaccurate altitude reporting is unknown, the FAA finds it necessary to obtain and evaluate additional information, and to require corrective actions in the interim until final action can be identified. In addition, the CAA has kept the FAA informed of its actions regarding the Mode "S" transponders. The FAA is in the process of reviewing the information from the CAA, and is considering separate rulemaking action to address those airplanes having Mode "S" transponders.

Explanation of Requirements of the Rule
Since an unsafe condition has been identified that is likely to exist or develop on other products of the same type design, this AD is being issued to prevent inaccurate airplane altitude reporting and false TCAS II advisories, which could result in the flightcrew deviating the airplane from its assigned flight path and a possible mid-air collision. This AD requires repetitive tests to detect discrepancies of the Mode "C" transponder(s), air data computer, and certain wiring connections; and corrective actions, if necessary. The actions are required to be accomplished in accordance with the procedures specified in the applicable component maintenance manuals and wiring diagrams contained in the airplane maintenance manuals.

This AD also requires that operators report all inspection results (positive or negative) to the FAA. Interim Action

This is considered to be interim action until final action is identified, at which time the FAA may consider further rulemaking.

Determination of Rule's Effective Date
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 AD action 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 99-NM-328-AD." The postcard will be date stamped and returned to the commenter.

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.

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, 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: