Question about the 737NG Engine start switch

[jjleo]

There is a question comes up in mind during a flight,
if I select the engine start switch as Ground instead of Continue, what will happen? will it broken the start motor or sth else?
And if we need to us e anti ice, is it ok use the FLT instead of the continue position?

[B737900er]

CONT = continuous use of the selected igniter ( left or Right)
FLT = continuous use of all igniters

The start switches are selected to prevent a flame out situation I believe so using FLT shouldn't be a problem.

Say you get yourself into severe turbulence you will put the start switches to FLT then you encounter icing so you put the TAI on.

[BOAC]

If I select the engine start switch as Ground instead of Continue, what will happen?

- it happened to me with an 'over-excited' Captain. Result?

Cry of 'NO!' from me
Cry of 'Oh S**T!' from him
Rapid return to CONT
Much tittering from RHS
Nothing else

Engineers told me the clutch would not engage

[de facto]

he got excited for a long time,cause you need to PUSH before you TWIST

Reedited from pull to push...got bit excited myself

[jjleo]

B737900er, thank you, it helps!

btw, will the switches automatically come to OFF like you start the engine on the ground when N2 above 56% if you do that in the air?

[EW73]

Well, almost....in the NGs I use, one needs to PUSH the start selector switch IN to select GRND.

[de facto]

The start switch solenoid will not energize therefore the start valve will not open and the clutch will not engage.
The DEU remove the electrical ground for the start switch solenoid as long as N2 is above 55 N2.

btw, will the switches automatically come to OFF like you start the engine on the ground when N2 above 56% if you do that in the air?

Yes

[BOAC]

Originally Posted by DF

he got excited for a long time,

- I'm not sure how to break this to you, but it takes most agile folk pretty much the same time both to Ground and Cont. If you find the action troubling, perhaps ask your co-pilot to do the start for you? Don't want you straining yourself. Wrist action can be vital.

[de facto]

perhaps ask your co-pilot to do the start for you? Don't want you straining yourself

They always do..

[BOAC]

Quite right to. I used to have them carry my flight bag and do all the walk-rounds, especially if it was windy or raining.

[de facto]

I make sure that if it rains they carry my flight bag around the aircraft and then B@@@ at them why its wet

[greg765]

Hey guys !

Reading this old topic, the following came to my mind:

- If I select CONT for the start switches and
- Select ignition on BOTH (not L or R).

Do we agree it would have the same effect as selecting FLT ?

In that case, why did they put a FLT position ? (as the same could be achieved with the CONT and BOTH combination).

There has to be a reason...

Thanks !
👍

[Check Airman]

Originally Posted by greg765

Hey guys !

Reading this old topic, the following came to my mind:

- If I select CONT for the start switches and
- Select ignition on BOTH (not L or R).

Do we agree it would have the same effect as selecting FLT ?

In that case, why did they put a FLT position ? (as the same could be achieved with the CONT and BOTH combination).

There has to be a reason...

Thanks !
👍

Now you're thinking like a Frenchman

[FlyingStone]

Originally Posted by greg765

In that case, why did they put a FLT position ? (as the same could be achieved with the CONT and BOTH combination).

There has to be a reason..

Good old American KISS at its best.

FLT is more or less only used when both engines have failed or when this could occur soon (severe turbulence). By providing pilots with FLT position Boeing has simplified the memory items by using one step instead of two.

[Capt Quentin McHale]

greg765,


Selecting CONT or FLT on the start system switches CONTinuously fires BOTH ignitors L and R irrespective of what ignition system selected for as long as you have CONT or FLT selected when engines are running.




Selecting BOTH on the ignition system switch enables BOTH ignitors (L and R) for the engine start sequence only. NB...EEC will operate BOTH ignitors (L and R) inflight automatically if it sees a possible flameout condition irrespective of which ignition system is selected L,R or BOTH. Hope this helps.


Rgds McHale.

[B737900er]

It may be also to do with dispatching with an INOP igniter and identifying the failed igniter.