The Flight Termination System (FTS), or Remote Termination System (RTS), is a fail-safe safety system for remote control and flight termination of airborne vehicles. It incorporates an output relay which changes state when commanded; this relay is maintained actuated under normal operating conditions, namely when an encoded radio transmission is successfully received. When the radio transmission is interrupted or becomes invalid for any reason, the receiver switches off the relay.

The relay contacts may be used to actuate a solenoid valve or other device, triggering a switch-over and setting the vehicle control mode to command a safe condition, such as a slow descent or hover manoeuvre.