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## FLARM Collision Avoidance System 

Mid-air collisions are a long standing danger in aviation and glider pilots have additional mid-air threats due to thermalling, cloud-street flying, and ridge running. All of these can put the glider in close proximity to other gliders and other aircraft. No matter how vigilant pilots are, too many stories of "near misses” exist. There are mid-air collisions or near misses each year in both club flying and in competition and between gliders and towplanes. 

As a way to mitigate mid-air collisions, the FLARM collision avoidance system was developed for glider pilots by glider pilots. FLARM warns FLARM-equipped pilots of impending collisions and gives the location of non-threatening nearby FLARM-equipped gliders. Figure 4-32  shows the interior of an ASW 19 glider with a FLARM unit on top of the instrument panel. It only works if both gliders have FLARMs. FLARM knows about the unique flight characteristics of gliders and stays quiet unless there is a real hazard. 

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FLARM (the name being inspired from 'flight alarm') obtains its position from an internal global positioning system (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 kilometers 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, into a database. 

Unlike conventional transponders in aircraft, FLARM has a low-power consumption and is relatively inexpensive to buy 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 provide 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. 

## Outside Air Temperature Gauge 

The outside air temperature gauge (OAT) is a simple and effective self-contained device mounted so that the sensing element is exposed to the outside air. The sensing element consists of a bimetallic-type thermometer in which two dissimilar metals are welded together into a single strip and twisted into a helix. One end is anchored into a protective tube, and the other end is affixed to the pointer that reads against the calibration on a circular face. OAT gauges are calibrated in degrees Celsius, degrees Fahrenheit, or both. An accurate air temperature provides the glider pilot with useful information about temperature lapse rate with altitude change. A very fast reading OAT gauge can give glider pilots another indication of the hottest center portion of thermals for maximum loft and where the edge of the lifting currents are located. 

When flying a glider loaded with water ballast, knowledge of the height of the freezing level is important to safety of flight. Extended operation of a glider loaded with water ballast in below-freezing temperatures may result in frozen drain valves, ruptured ballast tanks, and structural damage to the glider. [Figure 4-33] 

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