Whats that standby ignition good for?

[Guest s_L_Y_F_a]

Manual says: "Standby bus will automatically providepower if main bus fails."Ok, this is quite understandable but which bus is the main bus?Furthermore, what are the meanings of these three different positions (1,NORM,2) you can select with the standby ignition selector?Thx in advance

[Qavion 19]

Hi, Paul...There are 2 ignition systems for each engine (Ignition Sys 1 and Ignition Sys 2). Normally, 115V AC Bus #1 feeds Ignition Sys #1 and 115V AC Bus #3 feeds Ignition Sys #2.With the Standby Ignition Switch in NORM...If AC Bus #1 fails, then Ignition Sys #1 (on all four engines) will be powered by the Standby Bus.If AC Bus #3 fails, then Ignition Sys #2 (on all four engines) will be powered by the Standby Bus.Note that losing a bus is very rare. All generators feed all busses on the 744, except during Autoland.When the Standby Ignition Switch is selected to 1 or 2, the Standby Bus will power the selected (1 or 2) Ignition system on all four engines.If you lose Main AC power (1 & 3), then, irrespective of Standby Ignition Switch position, Standby Power will provide power to both (#1 and #2) Ignition systems.Hope this makes sense.Cheers.Q>

[NJ_Flyer 3]

Just to follow on from that. Most operators will selcted 1 ignition system for engine start up on one flight, and then select ignition system 2 on the next.

[Qavion 19]

"Just to follow on from that. Most operators will selcted 1 ignition system for engine start up on one flight, and then select ignition system 2 on the next."What sort of an ignition system are we talking about here, Ryan... This sounds like a 767 procedure???The Standby Switch shouldn't normally be touched on the 744. The EEC's control ignition switching automatically (cycling between sys 1 and 2 on each leg... and controlling single/dual ignition as required).Cheers.Q>

[Guest s_L_Y_F_a]

thx for the very informative replygod bless PMDG forum