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1: Traffic Collision Avoidance System. A computerised system in a modern airliner which utilizes radar, transponder data and in-system logic with the aim of providing collision avoidance if Air Traffic Controll fails to.

2: The alarm itself in the cockpit
1: The Aircraft was fitted with a state of the art TCAS

2: The pilots were alerted to the situation by the onboard alarm, audibly sounding off "TCAS ALERT; TCAS ALERT", Their quick response warded off disaster.
by Trent Hopkinson June 04, 2005
No, not Teen's Choice Awards. TCA is a shortcut for "take care always".
I have to go now, bye! TCA!
by thoughtful9311 August 28, 2009