B737 Takeoff Config Warning

[LEM]

Sometimes during taxi out, the LEADING EDGE FLAPS TRANSIT LIGHT remains illuminated, although actually they are all extended - confirmed by a visual inspection and the overhead annunciator panel.

Will the takeoff config warning be activated in this case?

Is it connected to the light on the center instrument panel, or to the ones on the aft overhead panel?

When that happened to me, the amber light went away after a few seconds, but other colleagues took off with the light on...

[Shaka Zulu]

Take Off Config warning doesn't go off.
It's not connected up to the lights in the front dash but to the unit that monitors and moves the LE Flaps.
Signal runs via 2 different lines to the 2 indication systems in the flight deck.Take-off permitted in case our overhead is correct and LE light on front dash is amber.

[avioniker]

It will depend on the build generation of the particular aircraft and what is being used as the configuration sensor.
In the NG the warning comes from the PSEU which is the same source as the transit light. You will get the warning.
Some older aircraft still have the switches in the slat actuators for the position sensing to light the extend light and different switches to activate the TO warning. In that case you won't get the warning.
There are five configurations that I've worked and they all have different configurations and mechanisms to provide the indications and warnings.
I have no idea how many TO warning configurations there may be when you consider that some aircraft may actually have a retrofit system installed because they were built for a customer who didn't want it and it wasn't mandatory yet.

[B73567AMT]

On our B737CL aircraft, if a flap sensor were to indicate an incorrect position that made the IN TRANSIT light illuminate, you will get a TO config warning as well when throttles advanced.

[80/20]

LEM said: Sometimes during taxi out, the LEADING EDGE FLAPS TRANSIT LIGHT remains illuminated, although actually they are all extended - confirmed by a visual inspection and the overhead annunciator panel

…..One of the most common snags on the 737, especially during winter with frequent de-icing fluid remains around the le-devices. Normally it is a position sensor transmitter problem while the le-device is in commanded position. It might be permissible to fly with this problem per MEL but only after several checks. One of them is the stall warning system test. Indication problems will normally not cause takeoff warning even though the simplified FCOM description might lead us to belive this. But if you study the MEL and maintenance manuals you will see how it could give a false stall warning during initial climb-out. I have dispatched with this many times, never had takeoff warning but have had false stall warning and stick shaker just after takeoff which was unpleasant.

Some operators have the following text, for maintenance, in their approved MEL: Press Stall Warning Test Switches No.1 and No.2 and check that the stick shakers operate normally. If both stick shakers fail to operate normally, then open and collar the Stall Warning Asymmetry Mode circuit breaker on the P18-2 Panel and then repeat test in step…....

[LEM]

On thi site Pat Boone says that the microswitches for T/O config wrng (737 classic) are located only on slats 1 and 4.


Anybody can confirm this?
This might explain why sometimes the warning is triggered and sometimes not.

[80/20]

goood info ASFKAP!

[LEM]

Thanks mate for your professional reply.

That happened sone time ago on one of our 30 airplanes, I don't remember which one...

I won't forget the lesson for the next time.

Cheers

[B737MRG]

Hi LEM and other colleagues,

If you find any errors in my B737 Guide, please forward them to me ASAP. I am convinced that the B737 MRG contains several errors, so I'm looking forward to all your comments in order to improve my notes.

I checked chapter 15 on Takeoff Config Warning and it seems I indeed wrote LED Flaps 1 and 4, not slats 1 and 4...? Correct ?

Regards and looking forward to your feedbacks,

Patrick

[LEM]

You're right, sorry Pat.