Evaluation of TCAS II Version 7.1 using the FAA Fast-Time Encounter Generator model [volume 1]
April 29, 2009
This report documents the Lincoln Laboratory evaluation of the Traffic Alert and Collision Avoidance System II (TCAS II) logic version 7.1. TCAS II is an airborne collision avoidance system required since 30 December 1993 by the FAA on all air carrier aircraft with more than 30 passenger seats operating in the U.S. airspace. Version 7.1 was created to correct two potential safety problems in earlier versions. The first change focuses on the sense reversal logic. The second change focuses on avoiding "wrong way" responses to Vertical Speed Limit or "Adjust Vertical Speed, Adjust" RAs. Lincoln Laboratory evaluated the logic by examining more than eight million simulated pairwise encounters, derived from actual tracks recorded in U.S. airspace. The main goals of the evaluation were: (1) to study the performance of the revised sense reversal logic for encounters where one pilot ignores the TCAS advisory; (2) to determine if the revised sense reversal logic has an adverse impact on encounters where both pilots follow the TCAS advisories; (3) to determine if the change from "Adjust Vertical Speed, Adjust" advisories to "Level Off, Level Off" advisories provides a safety benefit for TCAS. Three sets of encounters were examined in order to fulfill these goals: encounters where both aircraft are TCAS-equipped and both pilots follow the advisories; encounters where both aircraft are TCAS-equipped and one pilot does not follow the advisory; and encounters where only one aircraft is TCAS-equipped. A detailed analysis followed by a summary is provided for each set of encounters. An overall summary is given at the end of the report.