Mandates: TCAS Change 7.1

March 5, 2015

There’s no question that Traffic Alert and Collision Avoidance Systems (TCAS) and Airborne Collision Avoidance Systems (ACAS) have had a significant beneficial impact on aviation safety since initial government-mandated implementations began in the mid-1990s.

TCAS is designed to reduce mid-air collisions between aircraft by monitoring the airspace around an aircraft for other aircraft equipped with compliant transponders, independent of air traffic control. The system can proactively warn pilots of the presence of the other transponder-equipped aircraft that may present a collision threat.

With Change 7.1, the European Aviation Safety Agency (EASA) estimates that mid-air collision risk decreases by factor of four.

Two primary safety-related issues are addressed in Change 7.1:

  • Based on a series of incidents between 2001 and 2002, including one collision, in France, Belgium, Japan and Germany, one change proposal (CP 112E) corrects an issue with TCAS-TCAS reversals. In prior versions, if an equipped aircraft was instructed by TCAS to descend and the “intruder” aircraft either was not equipped or was instructed by Air Traffic Control to descend, a collision could occur. The new version allows TCAS to reverse its instruction far sooner when it senses non-compliance from the other aircraft.
  • The other proposal (CP 115) changes the current TCAS II aural warning “Adjust Vertical Speed, Adjust” to “Level Off, Level Off.”

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