TCAS traffic-detection or avoidance system

The Honeywell TCAS is a traffic alert and collision avoidance system for aircraft, offered by Honeywell Aerospace as the TCAS II Change 7.1 solution. It detects other transponder-equipped aircraft in the vicinity, evaluates the risk of a mid-air collision and gives the crew traffic advisories and, when needed, resolution advisories with a clear vertical manoeuvre to follow.

The computer is the heart of the system. The TPA-100B TCAS traffic computer, in a 6 MCU version, 940-0351-001, and a 4 MCU version, 940-0451-001, complies with TSO-C119c and ETSO-C119c, and it meets RTCA/DO-185B, the Change 7.1 standard, as well as RTCA/DO-300 for hybrid surveillance. The 6 MCU unit supersedes the TPA-100A 940-0300-001 and the 4 MCU unit supersedes 940-0400-001, so existing installations can be brought to the current standard by a service bulletin that is either a software update or a combined hardware and software update, depending on the modification state of the unit.

Change 7.1 addresses two safety issues. The aural annunciation "Adjust Vertical Speed, Adjust" is replaced by "Level Off, Level Off", a single resolution advisory that asks the pilot to bring the vertical speed to zero instead of choosing one of several rates. The reversal logic is also improved, so that a reversal resolution advisory is issued on time when an intruder or the pilot does not follow the original sense, for example when the crew follows an air traffic control instruction contrary to the advisory.

Hybrid surveillance reduces the number of active 1090 MHz interrogations by using position data received by ADS-B from equipped aircraft. A near threat in both altitude and range is interrogated at 1 Hz, a near threat in only one of them at 0.1 Hz, and an aircraft that is not a threat about once per minute. This lowers frequency congestion in dense airspace. Detection range is up to 100 nm with the TPA-100A traffic computer and up to 150 nm with the TPA-100B and a display capable of airborne traffic situational awareness.

Honeywell lists the TPA-100 family for air transport and business aviation, and it forms part of the SmartTraffic family of ADS-B In functions. Operators and integrators of unmanned aircraft and eVTOL programs use airborne collision avoidance functions of this kind, together with ADS-B In traffic data, when defining detect-and-avoid architectures for aircraft that share airspace with crewed traffic.