A kill switch was a feature the Galactic Empire installed on some of their TIE fighters as an anti-theft measure. When activated, it would cause a fighter's wings to detach, making the cockpit crash if the fighter was flying in atmosphere.
In 2 BBY, during an undercover mission to extract several defecting cadets from the elite Skystrike Academy, Sabine Wren's first escape attempt, during a simulated dogfight in space, was thwarted by kill switches that Governor Arihnda Pryce had secretly had installed on all of the TIE fighters being used in the exercise. One year later, Sabine and her fellow rebel Ezra Bridger stole a prototype TIE/D Defender Elite on Lothal, which was equipped with a kill switch. Sabine discovered it when she was deactivating the fighter's homing beacon, and immediately told Ezra to land the fighter. As a result, when the switch was activated, the fighter's subsequent crash was not as bad as it would have been, allowing Ezra and Sabine to escape with the flight data recorder and hyperdrive.
- TIE Fighter Owners' Workshop Manual