737 Start Up

Hi,

Just been watching a couple of videos re 737 start up procedures and am curious to know how 737 users understand the actual start up. In the one video, the narrator sets the "ignition" to left to start the left engine and right to start the right engine. Now perhaps I'm completely off base but my understanding with the "ignition" is that in fact each engine has two ignitors, a left and a right and that this switch is not for selecting which engine to start but which ignitor to use. And of course there's a position to have both ignitors on for start or hazardous flying conditions. Please correct me if I'm wrong as I would like to have the correct idea.

Many Thanks

Rob

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Originally Posted by mounty

Just been watching a couple of videos re 737 start up procedures and am curious to know how 737 users understand the actual start up. In the one video, the narrator sets the "ignition" to left to start the left engine and right to start the right engine.

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No. You don't need to do that. I suppose it might not do any harm (?), but it certainly isn't the recommended practice in any of the manuals I've read.

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Now perhaps I'm completely off base but my understanding with the "ignition" is that in fact each engine has two ignitors, a left and a right and that this switch is not for selecting which engine to start but which ignitor to use. And of course there's a position to have both ignitors on for start or hazardous flying conditions. Please correct me if I'm wrong as I would like to have the correct idea.

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You are right. The normal recommended practice as I've read it is to use Left and Right alternately on each startup. I flip it over after shutdown at the end of each flight so the other circuit gets used next time. This is to ensure that both are working -- you'd soon determine when there was a fault. As you say, you would only use the "both" position in hazardous restart conditions where you really needed to be sure -- if you used it regularly you'd never detect a failure in one of them.

Regards

Pete

Thanks Pete, I thought for a moment I had it wrong!!

Rob

There's also a thumb rule amongs most pilots:
On even calendar days you use the right ignitors switch position and on odd days the left. So the both ignitors are used in a balanced way, even if different crews are flying the plane.
But, this is not an official procedure!

There are two independent AC ignition systems, L & R. Starting with R selected on the first flight of the day provides a check of the AC standby bus, which would be your only electrical source with the loss of thrust on both engines and no APU.

Reference:

http://www.b737.org.uk/powerplant.htm#Ignition

Regards

Ruediger