727 Standby Ignition

[JammedStab]

It is briefly mentioned in my manual but haven't seen when it would be used. Apparently battery powered off Standby AC Bus.

Any 727 experts out there?

[JammedStab]

I would have phrased that differently (i.e. 'still alive'). :}

Each JT8 engine had two ignitors, one capable of being battery powered for a ground battery start when the APU was on the 'fritz' (and no external electrical available). (assuming you had external air)

Kept an engine running at San Angelo, Texas once for this very reason (i.e. no external air or electrical available and a questionable APU).

Thanks, found it under Battery Start Checklist. No APU generator and no GPU available is when you do it as said. I think I used to know that.

It appears either igniter can be selected but only one at a time based on selector position. I suppose only the engine being started gets ignition as it is based on fuel lever position.

[Kuchan]

http://aircraft-support.********.co.uk/2010/03/jt8d-ignition-system.html
The are two types of system on the 727.
a) The standard 20-4 Joule system that has a single exciter box.
It's supplied by 115V AC and 28 V DC. The 20-4 joule exciter can operate in the intermittent or continuous mode. In the intermittent mode, it fires both igniters. In the continuous mode it only fires the igniter in combustion chamber 7.

b) The Dual 20 joule system has two exciter boxes bolted together (Sometimes called a Twin Pack).
Both are supplied by 115V AC. One fires the igniter in chamber 4 the other chamber 7. Two exciters can be operated individually or at the same time. Earlier models were for intermittent use only. Later models are continuous. Remember 10min on LH the 10min RH for the earlier systems.

[aviatorhi]

Just to add on a little,

You'll get (high energy) ignition on BAT only. You need STANDBY power so the engine gauges tell you something useful instead of staying put.