The commercial need to standardise aircraft power supplies has resulted in virtually all modern aircraft (with the possible exception of certain light aircraft) being equipped with a 115/200 volt, three phase, 400 Hz ac primary power system. This is invariably supplemented by 28 volt dc and 26 volt single phase 400 Hz ac secondary systems. If this is the case why is there so much controversy concerning power supplies for avionics and why is there criticism of present day power systems whose performance is so superior to that achieved only two decades ago?

There are two basic reasons for the present situation.

Firstly, development of sophisticated avionic systems has resulted in increased susceptibility to certain aspects of the power supplies and this, coupled with the ever increasing application of avionics for the basic control and safety of the aircraft, has highlighted interface problems with power supplies.