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 with more than 30 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 through pilot reports, and applied research activities. Version 7 of the MOPS was implemented globally. Currently, two thirds of the US commercial fleet is TCAS Version 7 equipped.

Critical Safety Need: In certain encounters between two aircraft, TCAS does not issue a sense reversal (e.g. change a Climb command to a Descend command) in a timely manner, if at all. RTCA has reconstituted its TCAS Special Committee (SC-147) and tasked them with correcting the Reversal Logic Problem within the equipment.

Most Recent Accomplishments

Philadelphia (PHL) test site for TCAS Resolution Advisory (RA) monitoring installed (April 2008)