737NG Autothrottle Disconnect After Engine Failure

[Ziggy]

Losing an engine after V1 the autothrottle on the 737NG trips off at a certain point during climb out. I've seen it happen in the sim every time and never gave it another thought. Just recently went through my systems manual again and, after going up and down through chapter 4 several times, I couldn't find any reference to this feature. Can somebody help me out on this? What exactly trips the A/T and at what point? It's not in my book (I think).
Would it be right to assume that the autothrottle trips off solely so you don't forget to change rudder pressure when you manually reduce thrust for level off instead off the autothrottle reducing thrust and you going sideways.

Greetings, Z.

[The Greaser]

Ziggy. there is no automatic trip off of the autothrottle, it has to be done manually as the first step in the QRH drill for engine failure.

[Ziggy]

Greaser,

that's true, but in my SOP's, since there's no recall items/memory drills for a 'normal' engine failure (with no fire or severe damage off course) the QRH drills are not performed untill after cleanup.......so climbout to 1000 AGL first and then acceleration to bug up, this will take a couple of minutes.....by that time the autothrottle on my plane has disconnected already automatically.

Z.

[alexban]

The a/t will disconect if a/t fault is sensed by the a/t computer. If what you said about autodisconect during engine failure (i didn't notice,sorry) ,one possible cause that I think of will be electrical failure,maybe due to gen off bus. It's just a guess,though.
And this is for the classic.I will check the ng fcom for diferences.

ps. edited. yes ,as techman says ,the ng has also:"
significant thrust difference along with control wheel roll input of 10 degrees or more,flap up to 10" ,as a cause for at disengagement. So this is your case.

Brgds Alex

[Techman]

From a 737NG manual

Any of the following conditions or actions disengages the A/T

Moving the A/T arm switch to OFF
Pushing either A/T disengage switch
An A/T system fault is detected
Two seconds have elapsed since landing touchdown
Thrust levers have become seperated more than 10 degrees during a dual channel approach after flare armed in annunciated
Significant thrust difference along with control wheel roll input of 10 degrees or more, and flap position up through 10.

It sounds like the last case is what you are looking for.

[Ziggy]

It doesn't look like a failure to me. It doesn't happen immediately when the engine fails or when power gets transferred, but everytime more or less at the same point, my guess is at 800' RA, when THR HOLD normally changes in ARM. Maybe it's an optional feature my company elected to put in the plane that most others didn't, like we have the speed and altitude intervention buttons on the MCP. It's either that or I'm going crazy.
Thinking about it, it does make sense that the A/T disconnects itself. If the autothrottle was still in it would reduce to the climb N1 at 1500' AGL which is not helping off course. When the flaps are up normally max continuous thrust is selected in the FMC and then set manually, so you would disconnect the A/T there otherwise, but I'm sure it already disconnected itself before you reach that point.
Or is my company's SOP the only one not performing QRH steps untill after flaps up after an engine failure.
Unless somebody gives the answer here, I will post my findings after my sim next week.

Ziggy.

Just missed that reply from Techman.

My manual says the same thing, and on the newer ones the flap 10 or less restriction is even removed. But, I have a hard time believing this is the cause because I don't think I fly with 10 degrees roll input, maybe only the first second before rudder is applied.
The A/T disconnects well into the flight, as I said at about 800 AGL, when I'm fully trimmed and definitely don't have 10 degrees of roll input on the controls.

Ziggy