On November 4, 1999, the Federal Aviation Administration (FAA) issued AD 99-23-22, amendment 39-11418 (64 FR 61493, November 12, 1999), as revised by AD 99-23-22 R1, amendment 39-11473 (64 FR 70181, December 16, 1999), applicable to various transport category airplanes equipped with Mode "C" transponder(s) with single Gillham code altitude input. That 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. That action was 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. Such false advisories, if not corrected, could result in the flightcrew deviating the airplane from its assigned flight path and a possible mid-air collision.\n\nActions Since Issuance of Previous AD\n\tThe compliance timefor the initial test of the Mode "C" transponder(s) with single Gillham altitude code input, as required by AD 99-23-22 R1, has passed. Therefore, the FAA assumes that the test has been conducted at least once, and all applicable corrective actions have been accomplished, on all transport category airplanes affected by that AD. The following is a summary of the airplane inspections and test results:\n\nAircraft Test Results (AD 99-23-22 R1)\n\tAircraft test results reviewed = 1,142 \n\tAircraft passing tests without corrective action required = 1,055 \n\tAircraft failing tests with corrective action required = 87\n\tPercent of aircraft that failed the AD test = 7.6%\n\nAircraft Wiring/Avionics Failures\n\tMode "C" transponder failures = 49\n\tAir Data Computer (ADC) failures = 14\n\tEncoding altimeter failures = 3\n\tGillham code wiring failures = 1 \n\tMiscellaneous wiring failures = 8\n\tFailures sources under review = 12\n\n\tThe results of the transponder tests required by AD 99-23-22 R1 revealed that numerous Mode "C" transponders failed the test, and many of the Mode "C" test failures have been determined to be caused by a particular transponder type. All other test failures reported by operators appear to be random and isolated.\n\n\tThe FAA concludes that continued repetitive tests on the applicable airplane models listed in AD 99-23-22 R1 are unnecessary since the corrective actions have been accomplished on all transport category airplanes identified in that AD.\n\n\tIn addition, the FAA has determined that the repetitive performance of the tests required by AD 99-23-22 R1 may result in increased or accelerated component wear, which could contribute to reports of incorrect airplane altitude.\n\nFuture Rulemaking\n\tOver 50 percent of the airplane test failures have been reported by operators to be caused by Mode "C" transponders. The FAA is conducting further reviews to determine whether a systematic root cause failure of that Mode "C" transponder exists. Based onthe results of these reviews, the FAA may consider further rulemaking to address potential problems concerning the Mode "C" transponder.\n\nFAA's Determination\n\n\tBecause the results of the tests required by AD 99-23-22 R1 have identified and corrected the causes of the identified unsafe condition, and because repetitive performance of the test may increase or accelerate component wear and contribute to reports of incorrect airplane altitude, the FAA has determined that it is necessary to rescind AD 99-23-22 R1 to prevent operators from performing unnecessary and potentially harmful repetitive tests.\n\n\tSince this action rescinds a requirement to perform unnecessary actions, it has no adverse economic impact and imposes no additional burden on any person. Therefore, notice and public procedures hereon are unnecessary, and the rescission may be made effective upon publication in the Federal Register.\n\nThe Rescission\n\tAccordingly, 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:\n\nPART 39 - AIRWORTHINESS DIRECTIVES\n\t1. The authority citation for part 39 continues to read as follows:\nAuthority: 49 U.S.C. 106(g), 40113, 44701.\n\n§ 39.13 (Amended)\n\t2. Section 39.13 is amended by removing amendment 39-11473.