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Guest wlwjr66

Uncommanded dive only in PMDG 737-800

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Guest wlwjr66

Hello,I have been 'operating' the PMDG 737-800 on my computer for over a year, however, within the past 3 days, whenever I engage autopilot CMD A/B or CWS A/B, the PMDG 737-800 (ONLY) goes into an uncommanded decent and dive. Again, this started 3 days ago and does with both the the keyboard as controls and yoke (but that should not make a difference). All other autopilot equipped aircraft work fine.Any suggestions? A removal and reload of the aircraft?Thanks,Walter

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You didn't mention which stage of flight this is occurring (right after takeoff, climb, cruise?).. Try using load manager to reset weights and cg, this is one difference between variants. I don't know of many others as far as the simulation is concerned.


Dan Downs KCRP

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Guest wlwjr66

It was all phases of flight, from just after takeoff, to cruise, to descent. The flight could have been trimmed for level flight or a certain profile of climb or descent, then when the autopilot engaged, the trim starts cranking nose down and off it goes. If anyone has had a runaway trim in a real airplane that is what it was like. I problem is now fixed. Whether the method I used remedied the problem for sure is unconfirmed, but it's not diving anymore as soon as the autopilot is engagedWalter

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Guest Tommy Hansen

I am now experiencing the same problem after flying the 737 for a year.What solved your problem? Or have anyone else a solution to a runaway A/P that takes the plane in a ucontrolably dive?I did try to reinstall,same thing! Going crazy here,737 is my number 1 plane to roam the sky with.Tommy

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Guest wlwjr66

Tried to send mail but only got back error messagesaying it was blocked by server and so on.Anyway,I havn't been able to fix the problem. Tried reinstalling and playing with the aircraft cfg file but to no help.I'll possibly just reinsatll FS9 itself I guess.TommyHey Tommy,It figures; sorry about that. My previous primary internet provider is being notorious for blocking legitamate emails with various excuses. The associated newsgroup is filled with very mad subscribers. Because of the email problems, I am in the process of changing my emails over to my new ISP and I've updated my information in this forum.You can reinstall FS9 if you prefer. That might work. I just duplicated what my experience was. Somehow, the trim got beyond the parameters of the simulator. I put in tons of nose up trim while holding level flight with the yoke; then engaged the autopilot. As soon as the autopilot was engaged the aircraft nosed over. I immediately disconnected the autopilot leveled off with pitch and trim, and re-engaged the autopilot...same thing..uncommanded nose down. I re-engaged it again...same thing.So to fix the problem, I ran the trim gradually back into the green arc adjusting pressure on the yoke. When I engaged the autopilot after less drastic subsequent uncommanded nose down pitches, I disconnect and systematically bring the trim and pitch further back to "equalibrium"...for back of a better term without the autopilot.Now my trim is squarely back in the green arc with no pressure on the yoke and the autopilot engaged, and the aircraft is flying straight and level.Please keep me advised. Walter

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Guest sgemp

I have been having the autopilot dive problem, hpoe someone can help me solve this problem?

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Guest wlwjr66

Hello,What seems to have happened is even though you can fly the aircraft without control wheel pressure with the trim adjusted autopilot off, the aircraft on autopilot has not adjusted for some reason. The first time I experienced this, it seemed to have happened over time. In my previous post you see that I recently recreated (duplicated) what I experienced during that situation with the nose down, diving pitch when the autopilot is engaged.So to fix it...while sitting on the ground crank in plenty of nose-up trim...beyond the limits of the trim position indicator for a few more seconds.Take off.......level off at a couple thousand feet using control wheel pressure and engage the autopilot. If it still pitches down when the autopilot is engaged....disengage the autopilot...then either adjust more nose up trim while holding the yoke for level flight or land and do the same. Keep doing this until, when engaging the autopilot, the aircraft no longer pitches over into a dive. You won't have to do this each time. Even upon subsequent PMDG 737-800 start-ups, it should fly level on autopilot.I guess to minimize this occurance from affects of trim adjustments over time is to make sure the trim is in the take-off arc before each takeoff....:).Like I said, the method above of adjusting the trim more nose-up beyond the limits of the indicator a couple times worked for me. Please let me know if this works for you. Walter

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>You won't have to do this each time. Even upon subsequent>PMDG 737-800 start-ups, it should fly level on autopilot.>>I guess to minimize this occurance from affects of trim>adjustments over time is to make sure the trim is in the>take-off arc before each takeoff....:).>>Like I said, the method above of adjusting the trim more>nose-up beyond the limits of the indicator a couple times>worked for me. Please let me know if this works for you. >>Walter>Hi Walter,Is there some sort of "memory" going on with the trim that causes this? Why does your "fix" solve the issue for that flight, and subsequent others?Thanks,John


Boeing777_Banner_Pilot.jpg

 

- John Drago

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Guest wlwjr66

Hi John,As a matter of fact, I had something typed kind of mentioning about there seems to be some sort of memory being stored at least as far as the aircraft trim is concerned. Since I am by no means an expert of how MSFS or the installed aircraft work on the inside beyond the basics, I deleted those lines. Other aircraft will fly fine on autopilot with this trim problem still occuring with the PMDG 737-800, so evidently there is "memory" of the previous trim settings stored just for this aircraft. Over time with trim adjustments, I guess it exceeds the limit of what the autopilot recognizes as tolerable for level flight. The strange issue, while all this is going on is that the aircraft can be trimmed for handflying and fly straight and level, but the autopilot does not recognize this. To answer your question, I have no idea why I was able to fix the the problem for not just the current flight, but for subsequent other flights. I just happened to try this it and it worked. When it was first posted that it happened again, I decided to see if I could recreate the autopilot uncontrolled dive which was successful even to where I shut down MSFS and started again. The PMDG 737-800 autopilot dive problems continued even after restarting MSFS. I concentrated on the trim, and I recognized after the first try at tweaking the trim nose-up past the trim indicator range lessoned the nose-down dive of the subsequent autopilot engagement. Then repeating once or twice more, the aircraft was no longer diving with autopilot engagement during later MSFS of PMDG 737-800 start-ups.Walter

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