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Interior of an ASW 19 glider showing a FLARM unit on top of the instrument panel

FLARM is an electronic device to selectively alert pilots to potential collisions between aircraft. It is not formally an implementation of ADS-B, as it is optimised for the specific needs of small aircraft such as gliders, not for long-range communication or ATC interaction.

FLARM (the name being inspired from 'flight alarm') obtains its position from an internal GPS and a barometric sensor and then broadcasts this with forecast data about the future 3d flight track. Its receiver listens for other FLARM devices within typically 3-5 kilometres and processes the information received. Motion-prediction algorithms predict potential conflicts for up to 50 other signals and warn the pilot using sound and visual means. FLARM can also store information about static aerial obstacles, such as cables, in a database. The FLARM serial data protocol is public, while the prediction engine of the FLARM is patented by Onera (France), proprietary and licensed to manufacturers. On the contrary, its crypted radio protocol cannot be copyrighted and has been cracked in 2008.[1]

Unlike conventional transponders in aircraft, FLARM has a low power consumption and is relatively cheap to buy (620 euro plus tax) and to install. Furthermore, conventional Airborne Collision Avoidance Systems (ACAS) are of little use in preventing gliders from colliding with each other because gliders are frequently close to each other without being in danger of collision. ACAS would give out continuous and unnecessary warnings about all aircraft in the vicinity, whereas FLARM only gives selective alerts to aircraft posing a collision risk. Versions are sold for use in light aircraft and helicopters, as well as gliders. However the short range of the signal makes FLARM unsuitable for avoiding collisions with fast moving aircraft such as commercial and military jets.

The Swiss Office of Civil Aviation (FOCA) published in Dec 2010: "The rapid distribution of such systems only a few months after their introduction was not accomplished through regulatory measures, but rather on a voluntary basis and as a result of the wish on the part of the involved players to contribute towards the reduction of collision risk. The FOCA recommends that glider tow planes and helicopters that operate in lower airspace should also use collision warning systems."

FLARM was founded by Urs Rothacher and Andrea Schlapbach in 2003, joined by Urban Mäder in 2004. First sales were made in early 2004. Currently there are over 22,000 FLARM-compatible units (around half of them produced by FLARM Technology, the rest by licensed 3rd party manufacturers who have now overtaken FLARM in current sales) in use mainly in Switzerland, Germany, France, Austria, Italy, the Benelux, Scandinavia, Hungary, Israel, Australia, New Zealand and South Africa. In the UK the telecom authority and Civil Aviation Authority confirmed in 2007 that FLARM was acceptable and so it is also being adopted there.

Recent devices can also act as flight recorders by producing files in the (.igc) format defined by the FAI Gliding Commission. Through an interface, some FLARMs can be linked to other devices to produce a spoken warning of potential threats in addition to a display. Graphic displays with moving maps have also been produced by other manufacturers which use the data to plot the position of nearby aircraft including their rates of climb and call-signs.

FLARM's unique technology is also used in ground-based vehicles, e.g. for all sorts of vehicles in surface-mining such as trucks, dozers a.s.f. These products are designed and produced by the Swiss-company SAFEmine Ltd.

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