Crowded Frankfurt airspace trialling wide-area multilateration

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Frankfurt region air traffic controllers have embarked on the second phase of a trial of wide-area multilateration (WAM) technology that promises to improve aircraft tracking in even the most congested airspace.

The concept is simple. Around Frankfurt, a dozen or so ground stations receive transmissions from aircraft passing through a 128x80nm region around the airport and feed all the data to a central server. The ground stations' internal clocks are so accurately synchronized that the nanoseconds of difference between receipt of any given signal is enough to calculate an aircraft's position to within 50m, less than a wingspan of many modern jets and far more accurate than radar.

Every aircraft flying has a transponder, so the system demands no modification of the airborne infrastructure. And, as it updates every second - while radar systems can only update every 5s or so, the WAM system, which is compatible with ADS-B, could be used to control aircraft even on approach at close separation.

Alexander Kulikow, one of the engineers working on the concept, believes that radar will remain the "backbone" of tracking surveillance systems, but sees several advantages to adding WAM. Radar, he notes, can have blind spots in mountainous terrain and so a WAM system could fill in such gaps. And, the added assurance of such a highly-accurate tracking system should enhance controllers' confidence in the most crowded airspace regions.

The system passed its site acceptance phase at Frankfurt earlier this year and is now entering a more rigorous trial. Thales has also supplied a system to London ATC, where tests are ongoing, and will be supplying the Lyon and Nice regions.