autopilot problems

[roarkv 0]

whats your weight and fuel?Roar

[downscc 1,327]

The problem is in between the last and next to last picture. In the next to last picture all looks well, airspeed in near Fr although it looks like quite a lot of pitch up but in the last picture you are already in trouble. Can't tell what is getting you in trouble. What should happen from next to last picture is you press the AUTOFLIGHT button and she will maintain about the same speed until climbing to acceleration altitude (set during TO INIT). Don't raise flaps until she starts accelerating, the PITCH AND TO CLAMP modes will stay magenta. Once she starts accelerating, then you raise flaps and finally raise slats above Sr.The white lettering for pitch and thrust indicate autopilot does not have control, confirmed by the 169 KIAS in the speed window.Are you raising flaps too soon, which puts you in speed protection mode? Are you setting stab trim to TO value?The transition to AUTOFLIGHT requires more attention than for the Boeings. Don't let the speed decay below Fr, keep flaps down until acceleration.I usually reset the climb thrust and acceleration altitudes to about 1200 AGL just to make things go smoother.Give her another try.

[Guest]

What happens when you do NOT arm PROF on the ground, take off, engage the AP after at 400 ft (not any sooner!) and PROF at 1500 ft? Just curious if that goes well.

[mfrantz 45]

What happens when you do NOT arm PROF on the ground, take off, engage the AP after at 400 ft (not any sooner!) and PROF at 1500 ft? Just curious if that goes well.

Arming PROF (and/or NAV) on the ground is not a requirement. Actually the ability to arm PROF on the ground is not available to all MD-11 aircraft, it is an airline option. It is absolutely acceptable to engage PROF mode manually after take-off. You don't have to wait until 1,500ft AGL, PROF can be engaged anytime above 400 ft AGL. With PROF engaged below 1,500 ft AGL (thrust reduction altitude), thrust will automatically change to CLB THRST when passing 1,500 AGL. Also, have a look at the manuals FCOM, page PT.20.2

[mfrantz 45]

ok here are some screenshots maybe youll find something wrongthis is befor takeoff autoflight- proff-nav are armedthis is befor V1 when thrust is engagedclimbing-still handflying the planeand here is the problem-when i hit autoflight again it just stalls

I see in the 4th picture that flaps are retracting. You shouldn't have retracted flaps that early. In the 3rd picture you are a bit too fast. Speed is at 180+, while it should be ~170 (=V2+10). The FR bug is green but this doesn't mean you should retract flaps because your speed should have been lower. Since you have retracted flaps the amber foot has come up to around 165 and once you hit AUTOFLIGHT the AP it tries to bring down your speed from 180+ to ~170 (magenta bug for V2+10), so you are close to the stall speed. It is therefore possible that if something goes wrong (AP overshooting the target a bit, some wind gust, etc.) you will end up stalling. Flaps should be retracted when your target speed (shown in magenta in FMS speed mode, or white with FCP speed) is above the FR bug and the speed starts moving away from the FR bug. If you are flying in FMS speed mode this will happen at acceleration altitude which is at 3,000 ft AGL. @Dan:In the 4th picture the white speed and altitude modes do not indicate that AP has no control. They indicate that PROF mode and FMS Speed mode have been disengaged. Actually in this picture the speed protection mode has been activated.

[Guest]

Arming PROF (and/or NAV) on the ground is not a requirement. Actually the ability to arm PROF on the ground is not available to all MD-11 aircraft, it is an airline option. It is absolutely acceptable to engage PROF mode manually after take-off. You don't have to wait until 1,500ft AGL, PROF can be engaged anytime above 400 ft AGL. With PROF engaged below 1,500 ft AGL (thrust reduction altitude), thrust will automatically change to CLB THRST when passing 1,500 AGL.

I know, that's why I wanted him to give it a try this way. I always engage PROF manually when in the air. Didn't know about the second part though (that you can already activate it at a lower alt). Still, I don't mind waiting until 1500: usually I am already passed that alt before I have the time to press the PROF button. :(

Flaps should be retracted when your target speed (shown in magenta in FMS speed mode, or white with FCP speed) is above the FR bug and the speed starts moving away from the FR bug. If you are flying in FMS speed mode this will happen at acceleration altitude which is at 3,000 ft AGL.

Interesting! I always simply look at the FR sign: when it becomes green (when the white line is above the FR sign) I raise flaps. I never ever had stall problems I have to say, but from now own I will watch the target speed and make sure I'll wait until that one is above and moving up from FR before I raise flaps.

[mfrantz 45]

Interesting! I always simply look at the FR sign: when it becomes green (when the white line is above the FR sign) I raise flaps. I never ever had stall problems I have to say, but from now own I will watch the target speed and make sure I'll wait until that one is above and moving up from FR before I raise flaps.

The point is that the whole take-off phase up to the acceleration altitude (3,000 AGL by default) is done at a V2+10 target speed. This is usually the same with the flaps retraction speed. So the FR bug will be at the same point as the magenta target speed. Regrardless of the mode you fly (AP engaged or not, FMS speed control engaged or not), you are supposed to stay at V2+10 until 3,000 AGL. Any variations in speed (hand-flying, wind gusts, etc) that make the actual speed raise above V2+10 will turn the FR bug green, but this doesn't mean you should retract flaps, if your target speed still remains at V2+10.Normal procedure is that you wait until acceleration altitude, then when speed starts increasing, FR remains green and you confirm that your actual speed is moving away from the FR bug, you retract the flaps.

Still, I don't mind waiting until 1500: usually I am already passed that alt before I have the time to press the PROF button

That's fine, but note that without PROF mode engaged thrust will not automatically be reduced from TAKE-OFF to CLB thrust at the thrust reduction altitude (1,500 ft AGL). So, if you don't engage PROF below 1,500 ft AGL TAKE-OFF thrust will remain (although not needed anymore above 1500 AGL) until you finally engage PROF mode. Thrust reduction can also be achieved by pulling the altitude mode (this engages a Level Change climb mode) at 1,500 AGL.

[Guest]

EDIT:Double post...

[Guest]

Thanks for the detailed additional information! Much appreciated!!! :(

[Guest shefer]

guys! thx for the detailed overview.i did everything you said: i didnt retract the flaos untill 3000 AGL kept the speed V2=10,after the magenta dot jumped up to the exceleration speed i hit autoflight again and there he goes! up and right into stall!

[Guest shefer]

any idea? any1??

[downscc 1,327]

Lets have a screen shot right after you press autoflight and then one right after you retract flaps.

[Leffe 4]

any idea? any1??

"Shefer"Still don

[Guest shefer]

uninstall??? do you think its a hardware problem??

Lets have a screen shot right after you press autoflight and then one right after you retract flaps.

the last pic is after hitting autoflightmaybe ill upload a video?? :(

[Paul_Smith 92]

Are you using F5 to retract everything? F5 will pull your slats at the same time which is not what you want. Use F6 to retract one notch at a time but only when you are 20 knots past the target speeds. If that works, pleasde let us know.Paul SMith.