Auto pilot will not hold heading

[Cfoley 4]

I have been having problems with PMDG 747-400X and 747-400 8i with holding the heading. I will have the auto pilot set and the plane always shifts 5 degrees or more from the set heading, usually to the left. I do have A/T Arm and F/D engaged, plus the Yaw damper is on. I was flying from JFK to RJAA and after 4 hours out over Canada, I did a slow descent from 32,000 to 29,000 and that is when all hell broke lose. The airspeed kept jumping suddenly from around 270 to 400, down again to almost stall speed, up again and then shoots way up instantly and then FSX says overstressed the 747 and I crashed! This only happens when I use PMDG 747. This is not the first time this has happened. Does anyone know what might cause that? It never happens when I use QW757. I checked other posts but could not find anything similar to my problem.CF

Edited January 2, 2012 by Cfoley

[Ioan92 63]

A shot in the dark tells me you entered a badly represented turbulence zone, and since FSX is terrible at reproducing turbulence correctly, you got just that.For your own good I highly recommend you turn off crash detection, it's poorly represented, and you don't want to get a crash after 14 hrs of flight because you hit an invisible wall now do you? ;)As for the heading i'm betting my money on your aircraft trying to compensate for the crosswind, It's always like that on my flights.Hope I was of use! :)

[scandinavian13 5,192]

Search 'PMDG' and 'weather' and you'll find a host of information on the issue.FSX weather can cause issues because turbulence and wind are not properly simulated.Third party weather add-ons' solutions to those problems can also cause issues with the way PMDG has simulated the autopilot behavior.There are work arounds to get it all sorted.

[Cfoley 4]

Thanks for the information. I will turn off the crash mode if FSX. After spending almost 3 hours and only to have it crash was frustrating because of the airspeed. But like I said before, it was instant, 1 second it was at 250 and shot up past 400 the next second. Has to be an FSX issue, I guess. I do use that real weather option in FSX. I think I may have a solution to the auto pilot being off course. I did an experimental flight and set a heading. When it strayed off course 5 to 7 degrees again, I turned the Bank Limit Selector a few degrees until the 747 was on course as established on the heading indicator and it stayed on course. I will also search "weather" in AVSIM if I can find any possible answers for the altitude problem.

[Cfoley 4]

As for the heading i'm betting my money on your aircraft trying to compensate for the crosswind, It's always like that on my flights.

I did not even think about that the aircraft was trying to compensate for the crosswind. I did not realize PMDG or FSX would have that capability. Edited January 3, 2012 by Cfoley

[Ioan92 63]

I did not even think about that the aircraft was trying to compensate for the crosswind. I did not realize PMDG or FSX would have that capability.

A classic example would be this:Notice how much the actual heading deviates from the route's heading.

[Cfoley 4]

Unfortunately, I don't know how you set up the heading for this the way you have it. When FSX tells me to head a certain direction, I set the heading and select auto pilot. It looks different in your image and looks on course to me. I don't know how to use the FMC/CDU for that matter. I really don't know how to teach myself to use it since it is too complex and the PDMG instructions are too confusing to understand. I haven't even mastered the ILS yet. I fly the 747 like I would when I was a private pilot flying a Piper Warrior 25 years ago. Of course that is not the real way to fly a jet, but I still have some learning to do as time goes on. It is kind of fun landing a 747 by the seat of your pants and only using the VASI lights as a guide! Flap settings is not problem while on final.

[scandinavian13 5,192]

Rest assured, the way you land is the way it's done by the pros 99% of the time. This whole idea the plane flies itself the whole time is a complete sim-ism.Don't let self-defeat get in the way of your learning. It seems like you've given up on reading the technical stuff because it seems difficult and it's really not. There are tutorials, and if those don't suffice, there's always YouTube (I'd avoid it at all costs, though - half don't know what they're talking about and most are squeaky 12 year olds).It's not the complexity that's the issue most often. It's trying to master the beast all at once. If you can fly it, you at least have that down. Setting up the FMC is cake in comparison. Just break it down in smaller chunks.

[Ioan92 63]

Unfortunately, I don't know how you set up the heading for this the way you have it. When FSX tells me to head a certain direction, I set the heading and select auto pilot. It looks different in your image and looks on course to me. I don't know how to use the FMC/CDU for that matter. I really don't know how to teach myself to use it since it is too complex and the PDMG instructions are too confusing to understand. I haven't even mastered the ILS yet. I fly the 747 like I would when I was a private pilot flying a Piper Warrior 25 years ago. Of course that is not the real way to fly a jet, but I still have some learning to do as time goes on. It is kind of fun landing a 747 by the seat of your pants and only using the VASI lights as a guide! Flap settings is not problem while on final.

The aircraft was following the flight plan but the high crosswind made it fly sideways (sort of). ;)

[fstulm 4]

Cray,Which way would you point the boat when paddling accross a flowing river as to get exactly opposite the river bank from where you started?Ionut Micu

[Airbrakes 0]

The digital readout shows your tracked path, not the actual heading. The tracked path is your path over the ground. Your heading (the direction the aircraft's nose is pointed at) is shown via the upside-down triangle on the compass rose.

Edited March 5, 2012 by Airbrakes