FLARM Collision Avoidance System Outside Air Temperature Gauge 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. 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. 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] 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  Figure 4-32.  FLARM unit on top of the instrument panel. Figure 4-33.  Outside air temperature (OAT) gauge. 4-18 40 20 0 60 80 100 120 140 -20 -40 -60 -40 -20 0 20 40 60