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  1. #1
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    737 NG Start Switches

    Hi,

    Looking for a bit of direction on when the various settings are used for the start switches. I have seen 2 different uses of the CONT setting - one after engine start and one just prior to take-off. Can you tell me which is correct. The other item is when would you use the FLT setting?

    Any help appreciated.

    Thanks

    Rob

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    500+ This must be a daytime job ian@737ng.co.uk's Avatar
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    Re: 737 NG Start Switches

    hi rob.....
    check your e-mail. i've sent you the amplified proceedures section from the POH in .pdf format which might help you out. just do a search on 'start switches'.
    rgds ... ian
    Mr. Ian. P. Sissons is hereby recognised as an Honorary Flight Sim Captain following his passing in February 2016. This is in recognition for his commitment to Flight Simulation.

    www.mycockpit.org Featured Builder August 2008 www.737ng.co.uk
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  3. #3
    500+ This must be a daytime job Sean Nixon's Avatar
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    Re: 737 NG Start Switches

    FLT is used for in-flight engine starts.

    I know that the engine start switches are placed in CONT for take-off and landing, but am unsure as to the normal position during flight. I cant see anywhere in the procedures that puts them in the OFF position after take-off.

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    Re: 737 NG Start Switches

    Quote Originally Posted by mounty View Post
    Looking for a bit of direction on when the various settings are used for the start switches. I have seen 2 different uses of the CONT setting - one after engine start and one just prior to take-off. Can you tell me which is correct. The other item is when would you use the FLT setting?
    CONT means "continuous ignition", and that position is normally used during takeoff, and on final approach and landing, merely as an extra safety precaution to reduce the chance of a flameout (fuel stops igniting spontaneously by normal compression effects). It is also switched on when passing through heavy rain or cloud conditions which might also induce the same condition.

    The FLT setting is only for in-flight engine restart, when the engine has in fact suffered from a flameout, or has been disabled after some emergency or suspected emergency, like a fire. It is basically a starter for use when the fans are already spinning.

    Regards

    Pete

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    Boeing Re: 737 NG Start Switches

    The normal position of the Start switches when the aircraft is in flight is the OFF position.

    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. Normally, in-flight, no igniters are in use as the combustion is self-sustaining. During engine start or take-off & landing, GND & CONT use the selected igniters. In conditions of moderate or severe precipitation, turbulence or icing, or for an in-flight relight, FLT should be selected to use both igniters. NG aircraft: for in-flight engine starts, GRD arms both igniters.

    The 737-NG's allow the EEC to switch the ignition ON or OFF under certain conditions:

    ON: For flameout protection. The EEC will automatically switch on both ignition systems if a flameout is detected.

    OFF: For ground start protection. The EEC will automatically switch off both ignition systems if a hot or wet start is detected.

    Note that older 737-200s have ignition switch positions named GRD, OFF, L IGN, R IGN and FLT while newer 737s use GRD, OFF, CONT and FLT. This is why QRH uses "ON" (eg in the One Engine Inop Landing checklist) to cover both LOW IGN & CONT for operators with mixed fleets consisting of old and new versions of the 737.

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