Abstract: An airport safety system is disclosed, comprising surface movement radar for monitoring the movement of aircraft and land vehicles on an airport, said surface movement radar providing a signal input to a computer arranged to identify from the relative motions of aircraft and vehicles detected by the radar in accordance with a pre-programmed set of rules an aircraft at risk of collision. The computer is also programmed to cause transmission by radio of an audible alert signal when a risk is predicted, said radio transmission being at a standard aircraft communication frequency, such as the standard ground communication VHF radio channel. The alert signal can alternatively be transmitted by one of a plurality of message transmitting devices arranged at different locations adjacent to airport runways and taxiways, each message transmitting device comprising a radio transmitter connected to antenna means arranged to radiate a signal within a predetermined area at the location.

Abstract: An airport safety system is disclosed, comprising surface movement radar for monitoring the movement of aircraft and land vehicles on an airport, said surface movement radar providing a signal input to a computer arranged to identify from the relative motions of aircraft and vehicles detected by the radar in accordance with a pre-programmed set of rules an aircraft at risk of collision. The computer is also programmed to cause transmission by radio of an audible alert signal when a risk is predicted, said radio transmission being at a standard aircraft communication frequency, such as the standard ground communication VHF radio channel. The alert signal can alternatively be transmitted by one of a plurality of message transmitting devices arranged at different locations adjacent to airport runways and taxiways, each message transmitting device comprising a radio transmitter connected to antenna means arranged to radiate a signal within a predetermined area at the location.

Abstract: A system for providing ground location messages to an aircraft equipped with a Marker receiver, comprising a plurality of message transmitting devices arranged at different locations, each message transmitting device comprising: a radio transmitter (81, 82) operating at standard Marker Beacon frequency and connected to antenna means arranged to radiate a signal within a predetermined area at the location; message storage means (76, 77) connected to the transmitter for storing a voice message to be transmitted thereby; and detector means (72) for detecting the presence of an aircraft within said predetermined area and for actuating the transmitter to transmit the voice message in response to detection of an aircraft.

Abstract: Simultaneous transmitter operation in a radio network is prevented by monitoring the signal received at the control position from the transmitter of the apparatus, this signal being delayed by the passage down land lines connecting the control position to its transmission antenna and the receiver to its control position. If a signal is received within a known time period from the time of commencement of a transmit action then it is assumed to be a signal from a remote transmitter and the operation of the local transmitter is aborted to prevent interference. The system is particularly useful where land lines and consequent time delays are present between the control position and the transmitter and the receiver and the control position.