Analysis of Real Airborne Collision Avoidance System Surveillance Parameters

Airborne Collision Avoidance System (ACAS) has become an essential part of civil aircraft’s avionics. The surveillance function of this system provides each aircraft with the position information of other aircraft in vicinity. In order to acquire the position data, the system sends standardized messages on 1030 MHz radio frequency and receives replies on 1090 MHz. Since this frequency band is shared among all surveillance systems used in aviation, it is becoming saturated with the constantly rising air traffic volume. As a result of this saturation the air traffic controllers may not receive all messages transmitted by an aircraft which would lead to inaccurate indication on the radar screens. In order to determine how much ACAS contributes to the overall frequency saturation, it is necessary to observe its behaviour in real environment. This paper should analyze a few selected parameters, such as ACAS surveillance range, nominal surveillance rate or ADS-B version and find out their real values. For this purpose real messages received at 1090 MHz receivers were used and evaluated. The results showed the real value of ACAS surveillance range is much higher than the value stated in technical standards. Other results helped to define the nominal surveillance rate and show that the version of ADS-B which is mostly used in real environment is ADS-B ICAO version 0. These findings can be used as inputs to the tool for RF channels 1030/1090 MHz loading analysis.