Traffic Alert and Collision Avoidance System (TCAS) operates independently of ground-based equipment and issues Traffic (TA) or Resolution (RA) advisories while providing aural warnings and a traffic display. Installed in aircraft meeting 14 CFR part 135, TCAS I is mandated for 10-30 passengers and TCAS II for more than 30 passengers. AC 20-151B governs its airworthiness approval, while ARINC DO-160E defines its environmental specifications. The unit weighs 11.5 lbs, runs on 28 VDC or 115 Vac, and functions within -55°C to +70°C, yet is inhibited below 10,000 ft.
Jim GoodrichPilot, Airplane Broker and Founder of Tsunami Air
Expert behind this article
Jim Goodrich
Jim Goodrich is a pilot, aviation expert and founder of Tsunami Air.
What is TCAS in aviation for helicopters?
TCAS is an aircraft collision avoidance system that builds a three-dimensional map of aircraft in the airspace, incorporating range, altitude and bearing. It is an on-board radar surveillance system that interrogates ATC and Mode S transponders. Other aircraft reply via the 1090 MHz radio frequency, providing identification, altitude, range and bearing data. The system warns the pilot through auditory alarms and cockpit displays, computes and displays a recommended vertical avoidance maneuver, and provides separation assurance throughout a predefined column of airspace.
Do military aircraft use TCAS?
Yes, military aircraft use TCAS. The military traffic avoidance system provides aircrews with continuous TCAS and IFF simultaneously. These systems aid in monitoring other transponder-equipped aircraft that present a collision threat, and the system alerts pilots when two aircraft come dangerously close to each other. MASS utilizes active TCAS II and fulfills the unique military requirement for formation flight and rendezvous operations within civil airspace without nuisance TCAS alerts. It facilitates formation flight and refueling operations. TCAS 2000 will be part of GATM for the C-5, and GATM programs on C-17s will be achieved by incorporating Honeywell ETCAS. Army, Navy, and Air Force utilize the IDIQ program to procure TCAS and TAWS.
Although the civil mandate does not apply to military airplanes, CMIC agreed on a revised ACAS policy for military aircraft. Airborne Collision Avoidance System, known as ACAS, is the last defense against mid-air aircraft collisions and is designed to increase cockpit awareness of neighboring aircraft. ACAS Xa will be the replacement for TCAS II, and ACAS Xo will be the collision avoidance tuned to work in closely spaced parallel approaches.
Does TCAS detect military aircraft?
TCAS does not detect aircraft that are not transponder equipped, nor aircraft without operating transponder, so a military jet whose transponder has failed or has been switched off remains unseen by the collision-avoidance logic. Military aircraft operate with their transponders off based on mission requirements, and when they do, no reply reaches the TCAS receiver.
When the transponder is on, military aircraft operating in civil airspace are visible to civilian ATC, and their transponders can reply to TCAS interrogations and in that mode they will trigger alerts just like any civil flight. Because regulations only cover civil aviation, no mandate forces military operators to leave their transponders on, and civil ATC does not detect military aircraft that choose to remain electronically silent. EUROCONTROL CMIC agreed on a revised ACAS policy for military aircraft, but the fundamental limitation remains: if the transponder is silent, TCAS cannot know the fighter is there.
What aircraft are required to have TCAS?
In the United States, FAR part 135 requires turbine-powered aircraft with 10 to 30 passenger seats to carry at least TCAS I whereas those with more than 30 passenger seats must carry TCAS II. Commercial aircraft operating under Part 121 and any large turbine aircraft weighing more than 33,000 pounds (14,969 kilograms) or having more than 30 passenger seats are required to carry TCAS II. A 1989 rule mandated that all U.S. passenger-carrying aircraft with more than 30 seats be equipped with TCAS II by the end of 1991. After 31 March 2002, any TCAS II installed in RVSM airspace must meet TSO C-119b Version 7.0 or a later version, and all U.S.-registered civil aircraft with an installed TCAS II system must be capable of coordinating with TCAS units that meet TSO C-119.
Internationally, ICAO mandated TCAS II for all turbine-powered airplanes with a maximum take-off weight exceeding 15,000 kg (33,069 lbs) or authorized to carry more than 30 passengers. Effective 1 January 2000, all civil fixed-wing turbine-powered aircraft exceeding 15,000 kg (33,069 lbs) or with more than 30 passenger seats were required to be equipped with TCAS II Version 7.0. From 1 January 2005, the threshold was lowered: all such aircraft exceeding 5,700 kg (12,566 lbs) or with more than 19 passenger seats must carry TCAS II Version 7.0. EASA harmonized with this standard, requiring ACAS II (effectively TCAS II version 7.1) for all fixed-wing turbine-powered aircraft that have a maximum take-off weight greater than 5,700 kg (12,566 lbs) or more than 19 passenger seats.
Modern TCAS II systems require a Mode S transponder, and TCAS operation depends on both conflicting aircraft having operable transponders as an aircraft without a transponder will not trigger a TCAS alert. Many smaller personal business jets are not legally required to have TCAS installed, and TCAS I remains a lower-cost option for commuter aircraft with 10-30 seats.
Jim GoodrichPilot, Airplane Broker and Founder of Tsunami Air
How many aircraft can TCAS track?
TCAS II can track as many as 45 aircraft and display up to 30 of them. Within a nominal range of 14 NM for Mode A/C targets and 30 NM for Mode S targets, TCAS II can simultaneously track up to 30 aircraft.
What is TCAS in aviation for helicopters?
Because helicopters have large rotors, an irregular fuselage shape, low speeds, high turn rates, and frequently operate over water at low altitude, most are not equipped with TCAS. These characteristics degrade conventional TCAS performance, so current TCAS is not used on most rotorcraft. Instead, ACAS Xr - where the ‘r’ stands for rotorcraft - has been developed to provide collision avoidance designed specifically for helicopters.
For commercial helicopter operations, the TTR-4100 is the first TCAS II system certified by both the European Aviation Safety Agency and the Federal Aviation Administration. It is TCAS II Version 7.1 compliant, certified to DO-178B and FAA TSO C119C, offers a 30-40 NMI traffic surveillance range, and gives pilots better traffic-threat awareness. TCAS II is used on Airbus Helicopters H160 rotorcraft and by Bristow in partnership with Rockwell Collins. The Acron Aviation TCAS 3000SP, a proven world-class TCAS II product line, delivers Change 7.1 enhancement and Airborne Separation Assurance System upgrades, reduces weight and power dissipation, and provides operating-cost savings while meeting the latest mandates for traffic advisory and resolution systems.
What was the first plane with TCAS?
US Airways 737 was the first aircraft certified with the AlliedBendix (now Honeywell) TCAS II system. Piedmont Airlines conducted the initial operational evaluation of TCAS in 1982. TCAS II was introduced in 1989, and the first production version, Version 6.0, was implemented in 1990.
