Autopilot Capturing The Vertical Profile

[Guest Mike_2011]

I've tried the ATL - MCO run and everything is a ok system wise, but when I ask the autopilot/autoflight to fly the profile, the FMA indicate correctly, but the aircraft pitches up to much then the airspeed gets into the alpha range then the plane pitches down and goes into MCT thrust to get out then pitches up and the falls back into the alpha range or the autopilot overshoots an alt restriction or ceiling as set on the MCP.

[Tabs 2,790]

Michael,Gonna need more information here - what phase of flight is this happening in? What exactly does the FMA on the PFD say? Can you post some screenshots of it happening?

[Guest JaredA]

Maybe I can help here :) for me it is occurring on takeoff, after following the tutorials instructions, FMA will have the commanded speed in magenta, thrust indications are CLB THRUST in magenta and first cleared alt on the MCP in white, I engage the autopilot, it flies fine after I retract the flaps and slats by following the indications on the speed tape thats when it seems to lose it and will not recover from the alpha range, while its trying to get itself out the autopilot will not capture any kind of alt, though it tries the pitching up and down always seems to under or overshoot.I'll try again and see if I can get some shots of it acting up.

[Guest JaredA]

As promised here are a few shots of the FMC setup and what the FMA looks like before and just after the takeoff attempt: Here are a few shots of what the flight plan page looks like after all data is entered. Here is what the FMA looks like with the ATS armed and on the runway.Shortly after climbing above 1000 RA here is what FMA looks like with the autopilot engaged with profile selected as the vertical mode:This is what it did after a min or so after clean up. This is in the turn after the first point on the Braves DP out of ATL. MD-11 slipping back into the alpha range. Last two are examples of the autopilot over or undershooting the MCP alt while still trying to recover from the alpha range, with the autopilot coming out of the FMC commanded speed.

[downscc 1,327]

I suspect FS9 wx variations. What are you using to smooth the wind shifts?Also, the picture climbing through 2900 ft the IAS is decreasing. I do not activate the autopilot until the IAS is stable on or slightly above the Fr speed, then I turn on otto and if he accelerates I then raise the flaps. Coming back and looking at this, I notice the very high pitch so it is possible you allowed the speed to increase too high above V2 and otto is pitching up to slow things down and if this is the case then he will most certainly over pitch. The MD11 needs to be handled a lot more carefully on takeoff that the Boeings. Pull the pitch up after rotation to keep the speed bug in the neighborhood of the Fr mark and everything else that follows will work smoother.The picture climbing through 6000 the IAS is much above the setpoint. How did that happen? Between 2900 and 6000 you accelerated from 167 to 275 KIAS... was that due to wind shift? Once you have that kind of upset going it is time to put hands on and settle things down.

[Guest JaredA]

Active Sky is what I use for weather, I'd have to check and see what the settings are in it for wind smoothing. Hmm, ok would it change anything if you armed profile before takeoff as the Martinair crew does? It might have been the wind here in ATL the last days has been blowing pretty good, but after the first picture showing the FMA after selecting otto and profile as the vertical mode, is what otto did I didn't touch the yoke after that, as a demonstration of what has happened till now. I will try and stabilize it a bit more before turning on otto next time.

[emvaos 13]

The pictures suggest a pitch-down command calculated by the flight director system, yet actual pitch remains at 24 degrees or so. Are you sure you are not overriding the autopilot by yoke intervention ?PMDG Options / Options /General/ Joystick Control : Set elevators/ailerons to NEVER and press OKAnother idea : Are you sure you have not accidentally gone into accelerated sim-rate so close to the ground ?Vangelis

[Guest JaredA]

Yes the override was enabled, but I'll turn it off for test purposes and no I never use time acceleration, I don't even know the keystroke for it, I don't need to know :)

[Guest JaredA]

Folks who might see this let these shots be a visual picture of what you do if you abuse the MD-11 LOL follow Dan's method and otto will love you. Thanks Dan.

[Guest Mike_2011]

Folks who might see this let these shots be a visual picture of what you do if you abuse the MD-11 LOL follow Dan's method and otto will love you. Thanks Dan.

Where is Dan post what is the solution?

[Guest JaredA]

Its the replay after my screen shots post, which is basically fly the plane enough to stabilize the speed.