The requirements of the first engine controllers were primarily to satisfy the needs of the engine and, almost as an afterthought, to consider interface with the aircraft and the pilot.

The latter resulted in the overwhelming plethora of ‘essential’ ground test-sets and cockpit instruments that we see today. In a performance and integrity conscious world, beset with ever increasing costs and sometimes decreasing maintenance personnel skills, the engine controller can no longer be considered in isolation from the rest of the system that it serves. The obvious ability of a digital system to self-check and diagnose itself, its interface with the real world, and to make intelligent decisions based on those tests, has enhanced the case for digital engine control.