Start of descent to Sochi, URSS, went alright initially. But aircraft didn't observe speed constraints. At the first altitude constraint at 5000ft she was whizzing along at 330 knots!

 

I couldn't find a way of getting control of the speed. I tried AutoFlight off, with throttles at idle in the quadrant. Then I tried 250 knots on speed knob and pulled this. No use. Then I turned off the AP and got warnings as expected. None of these gave me control and I had to go to full manual to land the plane rather bumpily...

 

I couldn't find a way of controlling the plane using the autopilot to effect heading and speed changes.

Maybe I missed something obvious,

 

I be glad of advice. Thanks.

Start of descent to Sochi, URSS, went alright initially. But aircraft didn't observe speed constraints. At the first altitude constraint at 5000ft she was whizzing along at 330 knots!

 

Your don't say what mode you were using for your descent..  profile or level change?  How far was the TOD from the 5000 altitude restriction ?

 

 

 

I couldn't find a way of getting control of the speed. I tried AutoFlight off, with throttles at idle in the quadrant

 

In this configuration speed will be controlled by pitch. Pitch up and use spoilers to add drag.

 

 

 

Then I tried 250 knots on speed knob and pulled this.

 

Unless you change your pitch angle, this will do nothing. The speed hold will only adjust thrust to maintain 250. If you have a steep pitch angle and speed higher than 250, the thrust will stay at idle, but there is no magic that will automatically slow you down. If you had tried Level Change with 250 knots selected in the speed window, and pulled the speed knob you should noticed the aircraft pitch up to slow to 250 then descend at that speed

 

 

 

I couldn't find a way of controlling the plane using the autopilot to effect heading

 

Perhaps posting some screenshots of your MCP might help. If you had turned the A/P on again correctly and selected heading hold or heading select you should be able to fly by the A/P

Peter, many thanks for your detailed reply. 

 

I have not flown the PMDG MD-11 very much but I have completed half a dozen flights successfully without major problems. I am a real world GA pilot so I know the general principles. 

 

Mode was Profile to start with. I switched to Level Change when it was clear that the FMS speed constraints were being exceeded.

 

I was unable to level the aircraft to hold altitude, or to control airspeed with the speed knob pulled out. I could not get the thrust to go to idle no matter what I did.  Eventually it was possible but only after I disengaged the autopilot completely (warnings on/off), deleted all flight data from the FMS, and set spoilers, flaps and gear down.

 

TOD was around 60 nm from FL350 to 5000ft constraint.  Plenty of time to slow down I would have thought.  The plane selected the TOD itself on the hockey stick down symbol in Prof mode. 

 

I didn't have the presence of mind to take a screenshot but I will next time. 

 

Trying to unravel what I actually did is liable to lots of errors. You could help me best by explaining the difference between the AutoFlight mode and the autopilot mode. I have never been able to use the MD-11 autopilot to manage heading and altitude changes without the autothrottle remaining active. That bit of kit seems to have a mind of its own where airspeed is concerned! 

 

Put another way, is it possible to disengage the MD-11 FMS completely so that I can fly the plane using AP for heading, airspeed and altitude such as I might need to do to fly an NDB or VORDME approach under ATC in the zone?

 

Thanks for your interest. 

Arming autoflight also armes the autothrottle.

 

But disengaging the autopilot does NOT disengage the autothrottle.

 

So, disengage the A/T separately (default A/T toggle key combination, for example).

With a 3° slope, you need 100Nm to descend from 35000ft to 5000ft. Did you reset the MCP altitude well before the TOD, let's say 20-30 Nm before the TOD. What i'm suspecting here is that you didn't reset the altitude, and while the aircraft flies, the TOD is constantly recalculated ahead of the aircraft until you reset the altitude. But if you wait too long to reset the altitude then, it's too late, and the aircraft cannot meet the vertical profile and speed restrictions.

 

Stephane

 

 

Stephane LI-THIAO-TE

Envoyé de mon iPad à l'aide de Tapatalk

TOD was around 60 nm from FL350 to 5000ft constraint

 

Like the other poster said, that is too tight to both get down and slow down.

 

 

 

You could help me best by explaining the difference between the AutoFlight mode and the autopilot mode

 

There isn't really any Autoflight mode. Pressing the Autoflight button once on the ground arms the A/T. Pushing the throttles beyond about 70%  N1 engages A/T in TOGA. Pressing Autoflight again once in the air (above 400 feet i think) engages A/P. There are separate buttons to disengage A/P and A/T. You can fly manually with A/T engaged or not. 

 

 

 

Put another way, is it possible to disengage the MD-11 FMS completely so that I can fly the plane using AP for heading, airspeed and altitude such as I might need to do to fly an NDB or VORDME approach under ATC in the zone

 

Yes:

when you change altitude, dial the new alt and pull the Alt button for level change or use VS. You are now out of Profile (FMS) mode.

 

heading....dial the required heading and pull the hdg knob, you are now out of FMS nav mode.

 

speed ... dial your required speed and pull the speed knob. You are now out of FMS speed mode.

..........If you are in level change at the time the A/P will use pitch to maintain the climb/descent at that selected speed with either climb or idle thrust from the A/T.

..........If you are in level flight or VS descent when you pull the speed knob the A/T will use thrust to maintain that selected speed.

 

Good luck and post again if you have any questions.

 

ps... the MCP knobs for ALT SPEED HDG can be pushed as well as pulled. Make sure you are pulling them.

With a 3° slope, you need 100Nm to descend from 35000ft to 5000ft. Did you reset the MCP altitude well before the TOD, let's say 20-30 Nm before the TOD. What i'm suspecting here is that you didn't reset the altitude, and while the aircraft flies, the TOD is constantly recalculated ahead of the aircraft until you reset the altitude. But if you wait too long to reset the altitude then, it's too late, and the aircraft cannot meet the vertical profile and speed restrictions.

 

Stephane

Thanks, Stephane

 

Hm... I selected the 5000 ft constraint early and the plane flew down the vertical path accurately according to the magenta dot. The TOD hockey stick was a long way off and the plane could have started down a lot sooner. I thought it was too tight myself and wondered how I could start the descent early without messing up the FMS's background calculations.

Peter

 

The plane could have started down a lot sooner had it wanted to!  Maybe when I set up the STAR this changed the original altitude constraint and I missed this. It could be an explanation,

 

Thanks for explaining the autoflight/autopilot operation, and for spelling out clearly how to disconnect the FMS. I thought I had done all that, but I've been around long enough to know that mistakes are easily made.

 

Best wishes,

Don't know if this would have affected the TOD calculation but did you set a speed/altitude restriction in the FMS DES page....ie 240 KIAS at 10,000 feet ?  I find that the MD-11 does tend to calculate the TOD point rather late for my liking (using FS9). So I usually descend (20-30 nm) early using either VS or level change. I can recapture the profile later if I wish. This ensures i have time to slow down without having to use the spoilers too aggressively.

Don't know if this would have affected the TOD calculation but did you set a speed/altitude restriction in the FMS DES page....ie 240 KIAS at 10,000 feet ?  I find that the MD-11 does tend to calculate the TOD point rather late for my liking (using FS9). So I usually descend (20-30 nm) early using either VS or level change. I can recapture the profile later if I wish. This ensures i have time to slow down without having to use the spoilers too aggressively.

 

No, I didn't set speed/altitude in the FMS DES page. I will check this in future.  I'm running FSX but I think the TOD is too late - I find this with other planes too. 

 

Good idea to use the level change to initiate descent early - I didn't realise it was possible to recapture the profile later.  I guess just keep an eye on the magenta dot and click on PROF when it centres. Maybe it does it automatically.  It will be interesting to find out!

 

Thanks again for all help, Peter.

If you wish to recapture the profile you will have to press the PROF button when the magenta dot is aligned. Once in PROF you can press the FMS Speed button to give speed control back to the FMS or stay with MCP speed control using the speed window and pulling the speed knb when you want to slow.

Thanks again, Peter.