Aviation Safety Letter 2/2004

Transponder Operation in a Non-radar Environment

In a radar environment, transponders are very useful in providing your position, speed, and altitude to air traffic controllers. The transponder also has another important purpose in the operation of the traffic alert and collision avoidance system (TCAS). A TCAS-equipped aircraft has the capability of interrogating your aircraft transponder and by doing so determines if a conflict exists. Once TCAS has determined that action should be taken to avoid a collision, it will give the pilot of the TCAS-equipped aircraft directions to follow to avoid a collision. In addition, some aircraft are getting fitted with on-board traffic advisory systems, which are cheaper than TCAS, but which monitor intruding aircraft transponders within a few miles. Therefore do yourself a favour and ensure that your transponder is turned on at all times, in radar and non-radar environments. You may not have TCAS or an on-board traffic advisory system in your aircraft, but others who do will be able to avoid you in case of conflict.

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