On descent a few days ago, I encountered this ;

The A/T was intentionally applying Asymmetrical Thrust.

This never happened to me before, and I don't think it is part of Normal Operations. I find it interesting, any ideas as to why this may happen under normal conditions? Thanks!

Learning day by day about his bird.

 

If I remember correctly, there was perpendicular wind flow to my direction of travel, but shouldn't yaw input occur before any changes in thrust symmetry?

I'm trying to use common sense if you notice lol.

 

I checked the Operating Manuals, and Training Manuals, and all portrayed information was about Non-Normal procedures.

I am on CMD A, with A/T Engaged, I din't have have direct control of the throttle column

How were the engines? I suppose if there was no difference in actual indications (N1, N2 or whatever AT will try to sync) then it might show to a fault elsewhere than in A/T,

Yea, I'd want to see the indications.

 

...but shouldn't yaw input occur before any changes in thrust symmetry?

 

 

No, neither should ever occur. Whatever the winds are doing, the plane should still fly straight through airstream it is in. The fact that the airstream itself may be moving will only mean the plane has to fly straight in a slightly different direction to maintain the required ground track.

fly straight in a slightly different direction to maintain the required ground track.

Wouldn't that be achieved with yaw input?

Otherwise how else will it maintain groundtrack?

 

 

Sorry guys, I don't have any pictures of engine data, only grabbed this.

Could it be that service based failures are kicking in?

Maybe your right engine is due or soon due for overhaul or just not producing enough thrust, so the assymetric thrust is kicking in to compensate.

 

I just recently explored the built-in service based failure system that runs in the background. Boy those guys at PMDG have done some great work on the base aircraft.

 

 

Frank Cooper

So A/T was on? The A/T should have disconnected when the thrust levers are positioned differently by >10 degrees.

Wouldn't that be achieved with yaw input?

Otherwise how else will it maintain groundtrack?

 

No. Think river current.

 

If you want to swim to the exact opposite point on the other side, you need to swim a bit diagonally. But you are still just swimming in the water, it is just water taking you with it.

So A/T was on? The A/T should have disconnected when the thrust levers are positioned differently by >10 degrees.

A/T still on in this shot,

 

No. Think river current.

 

If you want to swim to the exact opposite point on the other side, you need to swim a bit diagonally. But you are still just swimming in the water, it is just water taking you with it.

Ah, I see what you mean now.

Thanks much

That is a new one, usually only seen on the golden oldies from time to time.

 

I have to say I only regularly see a 1-2%N1 discrepancy at any one time.

Were you descending by any chance? If so, I assume your A/T was turned on but switched to ARM mode (after RETARD mode), in which you can manually move the levers (if set so in the FMC's PMDG settings - joystick throttle overriding NG throttle in ARM mode or in all modes). Do you have a single throttle on your joystick or one for each engine?

 

Just my assumption.

Were you descending by any chance? If so, I assume your A/T was turned on but switched to ARM mode (after RETARD mode), in which you can manually move the levers (if set so in the FMC's PMDG settings - joystick throttle overriding NG throttle in ARM mode or in all modes). Do you have a single throttle on your joystick or one for each engine?

 

Just my assumption.

Thanks for the input Aykut, I am using a CH Flight Yoke, with one throttle axis, the other two sliders I use for Spoilers and flaps.

 

I set the Override A/T to 'Never' in the FMC, I will try to recreate the scenario.