From the above aaib report
Electronic conspicuity and collision prevention
Electronic conspicuity involves the carriage and operation of devices such as transponders and ‘FLARM’ (a device developed initially for gliders). These devices make aircraft ‘electronically conspicuous’ to other aircraft which are equipped with the means of detection of, or interaction with, the equipment on the subject aircraft. These systems require electric power and the fitting of wiring and antennae, which demand spare capacity from the aircraft’s power sources; they also add weight to the aircraft.
Aircraft owners may fit equipment such as TCAS, transponder proximity receivers, and FLARM, which assist their pilots in gaining awareness of other aircraft around them, and, in the case of TCAS, provide guidance to assist in avoiding collisions. Some lightweight devices are available, including some which carry their own battery power supplies.
TCAS is in very limited use in recreational aircraft, transponder proximity receivers are used by a small number of pilots, and FLARM, although gaining popularity amongst glider pilots, is finding less widespread acceptance outside gliding. It is widely accepted that the introduction of TCAS in commercial air transport aircraft has markedly reduced the probability of collision involving a TCAS-equipped aircraft and another transponding aircraft