ATO Advanced Technology Development and Prototyping Group
Traffic Collision and Avoidance System (TCAS)
Description
TCAS I is a mandated system for aircraft with less than 31 and more than 10 passengers, with no resolution advisory.
TCAS II is a mandated system for all aircraft flying within the NAS and Europe with 30 or more passenger seats or maximum certified takeoff weight greater than 33,000 lbs. TCAS II includes resolution advisories (RA) to instruct the flight crews if a collision is imminent.
Purpose
In 1993 TCAS was mandated within the United States. This mandate came as a result of several notable midair collisions and near midair collisions that had occurred over the previous 19 years. Congress enacted two public laws during that time period which called for the development of an anti-collision system. TCAS was developed and mandated, thereby calling for Minimum Operational Performance Specification (MOPS) compliance DO 185 under Version 6.04A. Since that time, the MOPS had been modified to Version 7 in order to accommodate over 300 Change Requests and Problem Trouble Reports submitted against Version 6.04A. These problems were identified as a result of active TCAS monitoring in Europe and the United States, pilot reports, and applied research activities. Version 7 of the MOPS was implemented globally. US aircraft were not mandated to equip with Version 7, but Europe elected to mandate this version. Therefore, US aircraft flying into European airspace must have TCAS Version 7 avionics. Currently, two thirds of the US commercial fleet is TCAS Version 7 equipped.
Critical Safety Need: In 2004, RTCA reconstituted its TCAS Special Committee (SC-147), as the direct result of a TCAS-related crash in Europe and a near mid-air that occurred in Japan. The committee was tasked with examining these events to determine the cause and contributing factors. It was determined that TCAS suffers from a problem called Reversal Logic Problem (i.e., SA01). In certain encounters between two aircraft, TCAS does not issue a sense reversal (e.g. change a Climb command to a Descend) in a timely manner, if at all.
Based on limited monitoring in the U.S. and Europe, approximately 11 reversal logic episodes have been detected. The predicated rate of mid-air collisions associated with this problem is estimated to be once every four years, unless a fix is implemented immediately.
The Europeans have proposed a Critical Avoidance Safety (CAS) logic change known as Change Proposal 112E (CP112E) to improve the reliability of RAs. The FAA's TCAS Program should oversee the finalization and validation of a correction to this problem, update the TCAS II MOPS, and coordinate appropriate rulemaking with AVS for TCAS II equipage throughout the national fleet.
Most Recent Accomplishments
- Safety Risk Management Document (SRMD) signed by Safety Management System (SMS) panel October 18, 2007
- ATC Operational Survey Final Report October 31, 2007
