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Ken.Pascoe

Bug Report : ENG OUT Drift Down

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Hi - if anyone has any background on the following I would appreciate it.

 

Scenario

- FL290; PMDG B777-300ER/FSX; 340T; Distance to run to destination 900nm.

- ENG FAIL L (Severe damage through CDU->Aircraft/Failures/Engine/Programmed/ENG 1 SEVERE DAMAGE)

- Left engine runs down; right engine increases thrust to maintain speed until thrust reaches the CLB limit (as currently selected/displayed); speed decays slowly because there's not enough thrust on one engine - this is all expected and mostly correct behaviour.

- FMC VNAV ENG OUT prompt selected; Max alt 17996 displays; 170000 set in the MCP Altitude Selector; FMC modification Executed; THEN

- FMA SPD / ... / VNAV PTH engages; PFD selected speed is reduced by the FMC/VNAV to EO D/D speed (293 kts); aircraft continues speed reduction towards 293 Kt

- Thrust on Right Engine reduces; as speed approaches 293 kts; thrust on Right engine increases again to (what is now selected) the CON thrust limit;

- Drift down commences; speed decays slowly below 293 kts into the Maneouvre Margin. Screenshot below.

 

OE-DD-large.jpg

 

This is NOT the correct behaiviour for an engine out drift down.

 

After executing ENG OUT, the FMA should change to THR ... VNAV SPD. The rationale behind this is that the aircraft is entering a height minimisation loss mode. Obviously since you are above maximum single engine operating altitude descent is inevitable, but until such time as you choose otherwise (clear of terrain; fuel usage assessed) - you want the aircraft to descend as slowly as possible at the most efficient single engine operating speed.

 

- As such the FMA will engage in THR; the FMC sets CON thrust (max continuous); and the auto throttle drives the thrust to the CON thrust limit (it should already be there) and maintain that thrust; meanwhile

- FMA VNAV SPD engages and the elevators are used to maintain the selected speed, which the FMC will have selected as the OE D/D speed from the CDU (293 in the case above).

- The one time this regularly does not occur is when the aircraft is near the top of descent at the end of the route anyway and I've seen the aircraft descend in a pre-top of descent mode (1250 fpm) even though the correct steps for an OE D/D was actioned. Hence the distance to end of route mentioned above (well clear of the TOD point).

 

Has this been reported before? Is there a fix coming? Can anyone suggest the best way to bring this to the attention of PMDG - or is this it?

 

Regards Ken

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Is there a fix coming?

 

Can't have a fix if nobody reports it. See below.

 

 

 


Can anyone suggest the best way to bring this to the attention of PMDG - or is this it?

 

From the main website and from the intro manual:

support.precisionmanuals,com

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Interesting, I just tried this and the after activating the failure the FMA actually DID show THR and VNAV SPD. But about half to 3/4 of a second later it changed to the SPD VNAV PTH, then once reaching the E/O descent speed (211 knots in my case) the FMA showed R SPD and VNAV PTH, and was descending at about 300-400 FPM and engine N1 was at about 90% instead of 97%, (my CON thrust setting).

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Hi - if anyone has any background on the following I would appreciate it.

 

Scenario

- FL290; PMDG B777-300ER/FSX; 340T; Distance to run to destination 900nm.

- ENG FAIL L (Severe damage through CDU->Aircraft/Failures/Engine/Programmed/ENG 1 SEVERE DAMAGE)

- Left engine runs down; right engine increases thrust to maintain speed until thrust reaches the CLB limit (as currently selected/displayed); speed decays slowly because there's not enough thrust on one engine - this is all expected and mostly correct behaviour.

- FMC VNAV ENG OUT prompt selected; Max alt 17996 displays; 170000 set in the MCP Altitude Selector; FMC modification Executed; THEN

- FMA SPD / ... / VNAV PTH engages; PFD selected speed is reduced by the FMC/VNAV to EO D/D speed (293 kts); aircraft continues speed reduction towards 293 Kt

- Thrust on Right Engine reduces; as speed approaches 293 kts; thrust on Right engine increases again to (what is now selected) the CON thrust limit;

- Drift down commences; speed decays slowly below 293 kts into the Maneouvre Margin. Screenshot below.

 

OE-DD-large.jpg

 

This is NOT the correct behaiviour for an engine out drift down.

 

After executing ENG OUT, the FMA should change to THR ... VNAV SPD. The rationale behind this is that the aircraft is entering a height minimisation loss mode. Obviously since you are above maximum single engine operating altitude descent is inevitable, but until such time as you choose otherwise (clear of terrain; fuel usage assessed) - you want the aircraft to descend as slowly as possible at the most efficient single engine operating speed.

 

- As such the FMA will engage in THR; the FMC sets CON thrust (max continuous); and the auto throttle drives the thrust to the CON thrust limit (it should already be there) and maintain that thrust; meanwhile

- FMA VNAV SPD engages and the elevators are used to maintain the selected speed, which the FMC will have selected as the OE D/D speed from the CDU (293 in the case above).

- The one time this regularly does not occur is when the aircraft is near the top of descent at the end of the route anyway and I've seen the aircraft descend in a pre-top of descent mode (1250 fpm) even though the correct steps for an OE D/D was actioned. Hence the distance to end of route mentioned above (well clear of the TOD point).

 

Has this been reported before? Is there a fix coming? Can anyone suggest the best way to bring this to the attention of PMDG - or is this it?

 

Regards Ken

Are you a real world 777 pilot?

 

If not then you certainly seem to know a lot about how the 777 is supposed to work.

 

I think when you have questions this deep then it is better to contact PMDG directly.

Especially if you are already certain anyway that something is not as it should be.

And it does not matter if this problem has been reported before or not because the more reports PMDG get, the better......but as far as I know this has never been reported in the forums here.

 

If you are asking if some others can try your scenario to compare things before you submit a support ticket then that makes sence.

But for me, personally, to be tickled into trying things, the tone of your post needs to be less "I know this is wrong and I know I am right anyway".

 

 

To bring this to PMDGs attention open up your ops center.

Windows START/programms/PMDG/Operation Center.

From there you can submit a support ticket.

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I'm in contact with PMDG now. Unfortunately they are moving onto the 747-400 product and so a fix like this for the 777 release is unlikely, although we might see it in P3D.

 

Yes - I have 15 years or so on  the 777's (all of them) and about 9000 hours. I currently check/train in the simulator and the aircraft.

 

The PMDG product is so good - that it's things like this that for me really stick out.

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Yes - I have 15 years or so on  the 777's (all of them) and about 9000 hours. I currently check/train in the simulator and the aircraft.

 

That's what I thought.

 

Good thing that you are in contact with PMDG directly.

Like I said, when you KNOW something should be different then you might as well give them a heads up directly (I have done that with a few things and they were corrected in the next update).

 

cheers and welcome to the club.

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