737 Classic Autothrottle Self Test
 

We have one aircraft on our fleet that conducts an autothrottle self test when flap is selected for approach. The A/T light on the instrument panel will flash 2-3 times as part of this self test. Reference to this test used to be in our manuals however has for whatever reason been removed and I can find no reference to it any more.
Has anyone seen this in the FCOM and if so, could they cut/paste the text or PM me with it?
Cheers
Clack:ugh:

There is no autothrottle self-test, at least not one that manifests itself in the flightdeck.

What you are seeing is the usual A/T flashing amber meaning airspeed error. This is only active inflight when the flaps are not up and the actual speed is not within +10 or -5kts from commanded. You will see this every times you select flap 1 (from flap up) because you will also presumably select the speed associated with flap 1 which be about 20kts less than you present clean speed, hence more than 10kts over bug speed.

If you want to prove this, preferably in a sim, from clean speed select flap 1 it will not flash, now select the flap 1 speed and it will flash until your speed falls to within 10kts of it.

It is all in your FCOM.

S&L

Hi S & L,

Thanks for your response. There is only one aircraft on our fleet of 14 that does this. There used to be a reference in our FCOM for it, however it has been removed. It simply stated that this was "as installed" and was a self-test but did not explain what the self test was. Perhaps it is a self-test of the system you speak of.

Cheers

Clack

clack 100

This may be what you are looking for

"An automatic test of the A/T flashing amber function is performed if the A/T
is engaged and the following conditions exist:
-MCP SPD or FMC SPD is the A/T active mode
-More than 150 seconds after lift off
-Flaps extended

A/T amber light flashes for 2 seconds, remains extinguished for 2 seconds and then flashes for 2 seconds again"

That is straight from our ops manual, and the conditions are met when going from flap up to flap 1 as you describe.

That's the one!!!!

Since we only have one aeroplane that does it, our powers-that-be obviously decided we did not need to know about it :ugh:

Well done Excrab!!