Airspace Management

The pilots’ display on the Collins TCAS-II is combined with the vertical speed indicator (VSI) and comprises a simple representation of the aircraft in the centre surrounded by symbols representing target aircraft within the bubble. Coloured areas around the VSI show the pilot the climb or descent rate required to avoid a collision.

TCAS has become a controversial topic because it questions just who is controlling the airspace. Pilots are generally keen to support anything which may avoid a collision. Controllers, on the other hand, feel that pilots should advise potential conflicts to them and then let the controller sort it out. A survey carried out in the US showed pilots were advising ATC only after they had manoeuvred their aircraft to avoid the conflict.

In one case in the US, two TCAS equipped aircraft were converging at the same altitude and each pilot was given a Resolution Advisory warning. At exactly the same time, the air traffic controller was alerted to the situation and issued instructions to each aircraft. One pilot acted on the instructions, the other followed TCAS advice; both aircraft began to climb, still converging. Fortunately, one aircraft outclimbed the other and they passed safely.

Any aircraft within the Collins TCAS-II scan, but not a potential hazard, is displayed as a blue diamond outline. Also, its relative altitude is shown as a plus or minus symbol followed by two digits indicating hundreds of feet above or below. Should an aircraft come within 6nm laterally or 1200ft vertically, the diamond becomes solid. If TCAS decides the intruder will come too close in the next 35 to 45 seconds, the diamond changes to a yellow circle with an arrow showing climb or descent. At this stage, the pilot is also given an audible “traffic, traffic” warning.

When the system decides the offending aircraft will become dangerously close in the next 20 to 30 seconds, it enters the RA or resolution advisory stage. The symbol on the VSI becomes a red square and the pilot is given an audible instruction to avoid collision. This could be “climb, climb” or “reduce climb” etc.

As reported in Australian Aviation (July 1994), the US FAA was looking at using TCAS as a separation aid for air traffic controllers. In areas where there is no radar coverage, such as oceanic areas, controllers rely on reports from pilots to arrange separation and add a safety factor of several miles or time. If pilots report that they have definitely passed another aircraft, based on TCAS information, then instructions can be issued for descent or climb, saving many miles and/or minutes of en route manoeuvring. The jury is still out on exactly what manoeuvres are going to be approved and when.

In Australia, the CAA has no plans to make TCAS mandatory. However, some airlines and training organisations are taking the initiative and installing TCAS equipment. The Australian Aviation College at Parafield in South Australia has fitted a variant of TCAS to its fleet. Known as Traffic and Collision Alert Device (TCAD), the system has proved a valuable training aid as well as a safety device. Unlike TCAS, TCAD does not provide bearing information.

According to the College, the equipment encourages the trainee pilot to maintain a good lookout particularly in the busy training areas. When the TCAD alarm activates, the student is immediately reminded that he/she is not alone out there. The college also finds the device very useful when conducting navaid training and navex’s outside controlled airspace. Transiting aircraft or aircraft carrying out practice approaches over the same NDB, for example, can be detected and avoided. Rossair General Aviation installed 26 of the Ryan ATS 7000’s to the AAC fleet after extensive evaluation.

By the way, from our 2026 perspective, TCAS II is now globally mandated for almost all commercial transport aircraft. In Australia, the Civil Aviation Safety Authority (CASA) eventually mandated TCAS II for all turbine-powered commercial aircraft with a maximum takeoff weight exceeding 5,700kg or carrying more than 19 passengers. Furthermore, the industry is currently transitioning toward ACAS X, which utilizes satellite-based ADS-B data to provide even more precise collision avoidance.