New radar-like systems for safer skies
The United Kingdom’s main air traffic service provider NATS (formerly National Air Traffic Services Ltd) is now using wide area multilateration (WAM) in the North Sea off the Scottish coast for helicopter flight following. The system’s us is now also spreading in Australia.
In that busy airspace over 25,000 helicopter flights annually carry half a million passengers each year between Aberdeen Airport and the oil and gas operations in the North Sea. Low-level radar coverage only extends 80 miles off the shore, forcing controllers to rely on pilot’s positional radio updates provided every ten minutes. Also, established inbound and outbound flight paths are, in many cases, not the most efficient routes due to the lack of visibility to air traffic control.
To improve safety and efficiency, NATS Services required a solution that provided high accuracy radar-like surveillance that was also compatible with future technologies such as Automatic Dependent Surveillance – Broadcast (ADS-B). NATS selected Sensis Corporation’s wide area multilateration (WAM) to cover some 25,000 square miles of the North Sea with multilateration sensors placed on 16 oil platforms. One of the platforms is floating, making the development of the Sensis solution even more challenging.
Multilateration relies on signals from an aircraft’s transponder being detected at a number of receiving stations to locate the aircraft. It uses a technique known as “time difference of arrival” (TDOA) of individual transponder responses at a number of receivers. This establishes “surfaces” which represent constant differences in distance between the target and pairs of receiving stations, and determines the position of the aircraft by the intersection of these surfaces.
Sensis WAM uses multiple low-maintenance, non-rotating sensors to triangulate aircraft and helicopter locations based on transponder signals to provide air traffic controllers with precise aircraft position and identification information regardless of weather conditions. With a higher update rate and greater positional accuracy than traditional radar, Sensis multilateration provides effective surveillance for increased safety, capacity and efficiency of airspace. With its advanced processing techniques, a Sensis multilateration system uses the minimal number of sensors for a less complex, lower lifecycle cost solution. Additionally, each multilateration sensor deployed by Sensis supports ADS-B.
Although Multilateration is most often used to manage surface vehicle and aircraft traffic, it is now also acknowledged to be a viable alternative to automatic dependent surveillance (ADS-B) in many airspace environments, both for terminal area and enroute monitoring. To the aircraft operator it has the advantage that it can be used by any aircraft transponder, including Modes A and C, with which almost all general aviation aircraft are already fitted. This in notable contrast to the expected cost to aircraft owners of fitting ADS-B capable transponders if they become mandatory, which some owners complain would double the value of their light aircraft.
SENSIS WAM is now installed and operational at Sydney where it will replace the precision runway monitoring radar (PRM) used by air traffic controllers to monitor aircraft approaching the two parallel runways, and is also an element of Sydney’s terminal area monitoring. It has also undergone detailed trials in Tasmania as an enroute monitoring system, and that trial is expected to result in a permanent commissioning soon.
Airservices Australia is now considering a number of other possible Australian locations for installation of the system.
