Synchronic feedback circuit

The synchronic feedback circuit, along with the multi-loop stabiliser, was an essential component for a smooth rematerialisation of a TARDIS according to Romana I. The Fourth Doctor, however, chose to use neither. (TV: The Pirate Planet)

He later listed the synchronic feedback circuit as part of a list of top 5 TARDIS components that were always breaking. (AUDIO: Babblesphere) Later, Adric activated it when he decided to pilot the TARDIS to Heathrow Airport. (AUDIO: Iterations of I)