"If the battery fails the engines still rotate and the gene's are still producing power...all very well until the battery dies completely and the DC control circuits drop out and thats when you normally lose the AC and control!". .. .Not sure which big jets you're talking about" Rodders", but on the 747-400, the primary source of power for the DC control circuits (in the GCU's), is the permanent magnet generator on the Gen (The Main Hot Battery Bus only provides backup power to the GCU's: If the generators are on line, there should be a constant supply of power to this bus anyway).. .. .Cheers.. .Q.. . . . <small>[ 16 March 2002, 06:20: Message edited by: QAVION ]</small>