Hi!I've got a 737NG and there's a problem!When I engage the auto pilot, it moves the plane using elevators, not the stab, so the plane keep moving up and down, up and down, up and down...and then it stabilize. What is the problema? I use the A/P correctly. I have Windows 2000 with the update to pmdg works with, I use FS2004. Can you help me?Thank u very muchCaptain Renato

Wait, what? If the plane didn't use the stabs, you wouldn't move vertically, period. Do you mean that the AP has difficulty intercepting the climbrate, or are we talking once it reaches cruise altitude? Give us some more detail and I am sure someone here will be able to help (Spanish is my first language, so feel free to write it in Spanish if that makes it easier for you).Daniel P.http://www.precisionmanuals.com/images/forum/ng_driver.jpgThe official psychotic AA painter. :)

If you mean that the autopilot moves the airplane using the elevators instead of the trim (default MS planes use the trim) then you need to know that the MS autopilot is very wrong in this respect and that the real one as modeled on the NG does use the actual controls, not trim, to fly the plane. You should idealy have the airplane well trimmed before engaging the autopilot in the NG - I've never seen the kind of behavior you're describing though, so yeah provide more information on exactly what you're doing to make this happen...

Hi Ryan,Sorry but you are wrong about the 737 Auto Pilot pitch control. Initially the AP will move the flight control but the AP will also re-trim the horizontal stab to remove load from the elevator controls and maintain a neutral elevator/stabilizer trim angle. This is why you have a Stab Out Of Trim warning if the AP is not trimming the stab properly.Cheers,JohnBoeing 727/737 & Lockheed C-130/L-100 Mechanichttp://www.precisionmanuals.com/images/forum/ng_driver.jpg

Daniel,I appreciate your trying to help by suggesting the use of spanish, but that would prevent a lot of other people trying to help.

^ Well, my intention was to translate what he said to it was easier for you guys to understand...DPhttp://www.precisionmanuals.com/images/forum/ng_driver.jpgThe official psychotic AA painter. :)

Ryan... you are correct about MSFS not being realistic in this respect. The Stabilizer on a real 737NG (and on most aircraft) cannot move fast enough to control pitch in all circumstances.The Flight Control Computer(s) on the NG compute the elevator command (for a certain pitch manoeuvre) and compare it with elevator "authority" (how much elevator movement is available). If the elevator command is between 10 and 25% of the elevator authority for a certain time, the FCC supplies a nose up/nose down trim signal to the Stabilizer. It stops the signal when the elevator command is less than 2% of the elevator authority. The command may vary, depending on autopilot mode, how high off the ground the aircraft is, etc. There is no trim command when you are commanding CWS pitch (away from the neutral position), trim up/down commands are not issued if the aircraft is flaring (during autoland)... Trim down commands are not issued below 60', etc.So, as John says, the autopilot actually controls both the elevator and the trim when engaged.Cheers.Ian.

Well, the AP NEVER use elevators to pitch the nose up or down, because it causes an estrutural overstress, the AP moves the elevator at the maximum angle that they can move. The plane keep shaking up and down.Look, I take off normaly, climb about 20 degrees pitch up and stabilize at the filled altitude, when I engage the AP (the airplane is already trimmed).Thank you!

20 degrees pitch? Are you sure?

"When I engage the auto pilot, it moves the plane using elevators, not the stab, so the plane keep moving up and down, up and down, up and down...and then it stabilize. What is the problema?"Difficult to say, Capt. Renato...I used to have a similar stabilization problem until I added extra RAM to my computer. How much RAM do you have? (and what kind of processor do you have?)However, this doesn't explain why the trim isn't operating correctly. With the A/P disengaged, does manual trim operate normally?Cheers.Ian.

I think you guys misunderstood what I was saying - I was just trying to point out that the default MS autopilot using nothing but trim to fly the airplane, which isn't realistic. Obviously I'm not an NG pilot or maintenence engineer, but I wasn't suggesting that NG never uses trim while on autopilot, just that it's not using it as the only means of controlling the airplane...Ryan

I don't know if this is relevent or not but are you using real weather if so what is the generater. I personally had the problem of getting false weather at altitude I had a temperature of -117C OAT at FL370 over the Atlantic after just leaving Spain on a cross oceanic flight. I began to porpouse due to the engines being frozen I assumed. I cleared the weather and used just clear weather and all my problems went away. I was using FSMETAR with NOAA weather and registered FSUIPC. I guess it is worth a shot.

RenatoThis would occur if you select ALT HLD whilst climbing or descending. The FMC will try to hold the altitude at which you pressed it. If you are climbing or descending, the plane will then chase the altitude up and down until it eventually can hold the altitude.In this regard the autopilot is accurate but differs from the default (and incorrect) ALT HLD function in FS9 and most other add-ons. In those the aircraft will level out when this is selected.Maybe this helps.

So,My computer is:AMD athlon 1.1 Ghz Gforce 4more than 300 RAMI've adjusted the joystick trim, I think that I almost solve the problem, now, it's shake just a bit, but when I make some steepy turns, the problem comes back, the plane shake too much.Thanx

Hi,One thing comes to mind here. I had some troouble during beta testing with oscillations during flight. We tracked this down to trim settings and load configuration. Did you do any loading of this airplane using any external loading software?Could you check up your load configuration and also your center of gravity (CoG or CG)? If the CG is off limits the plane will of course become unstable. You can check both in the FS Aircraft menu.Hope it helps,