Hi,

I'm currently training failures with the PMDG 737 NGXu. I'm programming an engine failure at Vr, which works fine. I'm getting a severe engine damage then.
However at the same time the failure is activated the A/T disengages automatically and when I re activate the switch it deactivates itself immediately from alone again.

In this video at 5:35 min it is not happening.

Thank you very much!

 

Best regards Andi

Edited November 17, 20205 yr by 737Andi

That movie (while being extremely detailed and thorough, after all author is a 737 commander) was recorded with the older PMDG NGX, released originally for FSX in 2011.

if I recall correctly, an engine fire during T/O, the AT will measure discrepancy between thrust lever position and actual thrust output. Since B737 autoflight mantra is always to have the pilot in control, the AT will disengage, rather than moving the working engine lever which could lead to un-anticipated yawing moment if the pilot is not ready to compensate with rudder.

 

 

It's an option on AT computer:

if thrust differenct is enough to:

a) thrust lever different more than 10 degree, OR

b) along with control wheel roll input more than 10 drgrees

there are some option on Flaps setting and approach mode, but mostly this 2 condition.

It's added to prevent crashes like Bucharest(A310) and Guilin(B733)

But I thought PMDG might not simulated it very well, if I do the cross bleed start on the ground, I'd likely get a A/T disarm as well with about 35% N1 on ENG1, but IRL it never happends even at 40% of N1. I've ticketd them almost a year ago, but still not fixed yet....

Thank you for your replies!

 

I'm a little bit confused :(
I also posted this question on PPruNe (https://www.pprune.org/questions/636846-737-engine-cut-vr-t-disengages-automatically-why.html) and the guys over there said an automatic disconnect of the A/T does not happen?!
Maybe I'm just misunderstanding something.

Is there a way to enable/disable this feature on the NGXu?


How would I behave correctly now in case of an engine failure at rotation since the video is not showing the real behaviour?
I suppose I just need to pull the thrust lever of the affected engine back to zero and adjust the desired thrust manually with the working engine? So if the engine fails on Vr I suppose it would make sense to fully forward the working thrust lever to gain maximum climb speed initially. I just need to pay attention with the side rudder that the plane is not deviating to strong from runway heading due to the big difference in thrust. 

 

I would also like to understand the following....

17 hours ago, C2615 said:

if thrust differenct is enough to:

a) thrust lever different more than 10 degree, OR

Do I understand this correctly? ....if thrust output between left and right engine becomes bigger than the thrust difference that would arise when I set 10 degree or more on the thrust levers with normal operating engines, then the A/T disconnects?

 

17 hours ago, C2615 said:

b) along with control wheel roll input more than 10 drgrees

Not sure if I understood that correctly. If the plane is flown with a certain speed and I pull the Yoke more than 10° back the A/T disconnects because the resulting speed change cannot be compensated by the autothrust system?

 

Thanks!

the members at PPRune are very knowledgable so perhaps go with their advice? 🙂

reassuring AT-disconnect is one step (memory item) in the whole procedure of taking off with one engine, and I think it should be left disconnected (do not try to activate it again).

But as a simmer trying to accomplish the actual goal of the training: focus rather on aviate and navigate instead of why is one switch acting weird. This is foremost a hands-on drill, not button pushing.

Good luck 🙂

 

8 hours ago, 737Andi said:

1.Do I understand this correctly? ....if thrust output between left and right engine becomes bigger than the thrust difference that would arise when I set 10 degree or more on the thrust levers with normal operating engines, then the A/T disconnects?

 

2.Not sure if I understood that correctly. If the plane is flown with a certain speed and I pull the Yoke more than 10° back the A/T disconnects because the resulting speed change cannot be compensated by the autothrust system?

1. It's mostly for throttle  lever jam, not engine failure, like in the Bucharest or Guilin Crash.

2.The main condition for both a) and b) is thrust been different enought.

 

It's better if PMDG fix it (along with the cross-bleed event). but IRL the 737's AT could disconnect out of no reason at all (like the electromagnet on that switch get too hot...) and as pilot, you just need to prepar to manually take over it (or try to reconnect it if possible) at any time....

Hi..thanks again for your answers. I'm not saying anyone is wrong. Just trying to understand this plane as good as possible.

20 hours ago, 737Andi said:

How would I behave correctly now in case of an engine failure at rotation since the video is not showing the real behaviour?
I suppose I just need to pull the thrust lever of the affected engine back to zero and adjust the desired thrust manually with the working engine? So if the engine fails on Vr I suppose it would make sense to fully forward the working thrust lever to gain maximum climb speed initially. I just need to pay attention with the side rudder that the plane is not deviating to strong from runway heading due to the big difference in thrust. 

Would this procedure be half-way correct? If not..can you guys maybe recommend me a video tutorial or something similar. I was not so lucky with that on youtube. Or is there some recommendable detailed documentation somewhere? 

 

11 hours ago, C2615 said:

2.The main condition for both a) and b) is thrust been different enought.

I fear I dont get this. How does the yoke roll input effect the engine thrust output difference?

 

Thanks!

11 hours ago, 737Andi said:

I fear I dont get this. How does the yoke roll input effect the engine thrust output difference?

I'm not the guy who design it, but image like this:

You are cruizing level with AP on, low alert (as you shouldn't) and suddenly  engine No.2 quit, the aircraft yaw and then bank to the right the AP on 737 could not use rudder, so it use yoke left to fight it., as speed would also drop, the AT, it not disengaged would add power to the remaining engine to get back to speed, if AT keeps going, you are more likelt to get into a spiral or even spin...