View Full Version : B737 speedtrim fail / start switch

29th Mar 2015, 22:06

We had this question on our recurrent test. Can anyone comment or direct me to source of such information?

de facto
30th Mar 2015, 10:56
Answer is A

31st Mar 2015, 09:01
I believe so, but can we get some sauce of this information?

de facto
31st Mar 2015, 09:13
Whats your preference?ketchup or mayo?

31st Mar 2015, 09:26
If you're not sure of option A then look at the others; Options B and C are nonsense in the first 6 words. :)

Only the action of setting the start switch to Continuous will keep the EEC powered.

31st Mar 2015, 11:14
Well, I cannot find any sauce or source for this. Anyone?

31st Mar 2015, 14:03
Power Plant (http://www.b737.org.uk/powerplant.htm#Engine_Starting)

".....blank parameters which are controlled by the EEC and hence are only displayed when the EEC powers up when the associated start switch is selected to GND. During start-up the EEC's receive electrical power from the AC transfer busses, but their normal source of power are their own alternators which cut-in when N2 is above 15%."

31st Mar 2015, 17:32
"when the associated start switch is selected to GND."??

Nice sauce but not my kind of sauce.


31st Mar 2015, 18:14
Whenever the SW is used it powers the EEC and shows engine indications.

31st Mar 2015, 19:29
If we consider the SW to be true, still where is the link between the EEC and Speedtrim fail? I think thats about half of the answer. Mainly why?

in the meantime Urban Dictionary: Sauce (http://www.urbandictionary.com/define.php?term=Sauce)

de facto
31st Mar 2015, 20:43
Ok,just because you taught me some Essex slang which ill definitively use in the future,ill give a hint on the speed trim.:E
The speed trim needs the N1 info,otherwise how can it work? remember it is about speed stability,(low thrust-high speed--->stab trim gives nose up and high thrust-low speed--->speed trim sends info to the the stab trim to give nose down trim)
The EEC has that info,it uses it to control your engine thrust and provide that info toyour speed trim.

1st Apr 2015, 13:03
Don't happen to have a proper 'sauce' for the OQ, do you?

de facto
8th Apr 2015, 09:33
There is no direct answer in the FCOM,if that is the sauce you are looking for....
However,the Engine start switch powers the EEC via the engine start lever in Idle or if the engine start switch in GND or CONT.(AMM wiring schematic 73-22-11).
The second part of the question is the link between no N1 info and subsequent loss of speed trim...i believe i answered it above and one needs to find the interaction between the EEC and the speed trim function.
The EEC gets info of N1 directly from the sensors or via the DEU,if no input then speed trim has no info to work with..(AMM 22-11).