The L-3 Avionics TRC-791 Transmitter Receiver Computer is the primary unit of the TCAS-791 Traffic Alert and Collision Avoidance System. The TCAS-791 monitors the airspace around an aircraft and advises the flight crew of a nearby transponder-equipped aircraft that may pose a collision threat. The TCAS-791 system consists of a CD-605 Control Display Unit, TRC-791 Transmitter Receiver Computer, NY-156 L-band Directional Antenna and NY-152 an Omnidirectional Antenna. The TRC-791 can track up to 35 intruder aircraft simultaneously to a maximum closure rate of 1200 knots while displaying the 8 most threatening aircraft. The TRC-791 contains all the necessary circuitry to convert inputs into aural and visual advisories as well as Built-In Test Equipment (BITE) which can detect faults or failures verifying that the TCAS-791 is operational.

The TRC-791 is 6.39 inches wide, 15.08 inches deep, 7.62 inches high and weighs 18 pounds 13 ounces not including the mounting tray. The TRC-791 has a nominal surveillance range of 27 nautical mile and a maximum of 35 nautical mile and a display range of 5, 10, and 20 nautical mile when used with the CD-605. The TRC-791 operates at a maximum altitude of +55,000 feet and within a temperature range of -55°C to + 70°C.