I'm trying to do a 10 hour flight, created a flight plan in fsbuild, and imported it into the fms of the PMDG 747. after about 30 minutes the 747 started veering off the flight plan and making random s curves. I thought it might be because of sharp tight curves fsbuild had put in it, so I deleted the departure waypoints, and it soon had a nice long line and was following it fine. about 30 minutes later, it started making s curves again on either side of the acars map. What gives? I would presume that the 747 would be like every other aircraft, and simply follow a straight line. Am I doing something wrong here, or is this a known issue? 10 hours is a long time to sit here and baby a 747 with the heading indicator... Everything else is working just fine, so it's not an FSPasengers failure. Any ideas?

http://support.hifitechinc.com/Knowledgebase/Article/View/11/4/how-to-prevent-s-turn-issues-with-certain-aircraft-autopilots

 

http://forum.avsim.net/topic/410346-fsx-pmdg-747md-11-to-many-bugs-with-fmc-and-ils/

The first thing you want to do is look at the PFD to see if you lost HNAV lock. Also look at the RMI or EHSI nav display to check if the there are any deviations from VOR frequencies.

 

Next you need to check for engine performance and fuel planning to insure they are performing so thrust is matched from each.

 

Proof your flight plan in the fsbuild map pane. You may have to do two builds to allow for mouse zoom control if you lose it. Look for erratic headings especially due to navaid duplicate names. This is common in the airport area which uses non-exclusive waypoint labels which are local to the area, typically something like D020 and are included in the AIRAC files for the terminal procedures. There is a setting in FSBuild to limit the range of these.

 

Not very well documented in FSBuild is a setting that is not sticky between sessions. It is called build from route table. If you manually edit the table and build without this set it will ignore your table edits and rebuild from scratch.

 

Have a look at my hints for FSB which might help. I use the PMDG 737s.

 

fsb tips and update.pdf

 

Confirm no discontinuities on the LEGS pages and use the nav display plan mode to step through the nav display pages prior to take-off.

 

Any noisy control can act like the yoke was bumped and disconnect the AP functions.

 

It should be noted that while on the FMC it failing to receive raw data on navaids it should use the RNAV coordinates.

 

I don't know if the Queen by PMDG emulates the IRS (Inertial Reference System) but if so check that it was aligned prior to departure and check it. The B737 does not emulate this check.

 

Do you have any PMDG failures set? Don't forget to check hydraulics.

 

Keep an eye on airspeed and fuel tank balance.

 

Is rudder trim within range? Bank limiter set to allow tight turns?

 

I read the FS Passenger description and it looks like monitoring only, that is it can not control the aircraft.

 

At the moment that's all I can think of other than run without FS Passengers to confirm it can not cause a problem.

 

 

 

 

 

From http://support.hifitechinc.com/Knowledgebase/Article/View/11/4/how-to-prevent-s-turn-issues-with-certain-aircraft-autopilots (Most likely issue)

 

When using certain high-fidelity aircraft including PMDG 747, MD-11 or other high-sensitivity aircraft, turbulence effects can result in stability problems and potential s-turn autopilot hunting. Both FSUIPC turbulence effects and FSX internal turbulence effects (used by AS and FSX itself) can cause these problems. In order to minimize these harmful effects, it is recommended to minimize/disable turbulence effects in both FSUIPC (if in use) and FSX. 

 

 

FSX Turbulence does not act in the way real turbulence does (ActiveSky Next does it better, but still needs to be adjusted significantly down). In the real world, turbulence is a mix of convective (circling up & down) air and gusts (speeding up/slowing down) however there are eddies and currents in the gusts, with a 'core' of fast moving air mixing with adjacent and surrounding slower air.

 

In FSX the aircraft itself is moved "shaken" around a bit while the Indicated Airspeed is moved up and down at random.

 

PMDG's autopilot cannot decipher what to do with this, so it will react to being 'moved' to the left, by starting a shallow right turn to rejoin track. However as the shaking is random, and the autopilot only checks it's progress every few cycles, the autopilot can see itself 'moving' off for several seconds then only slowly react to this. It is not being 'blown' off course, but being shaken back and forth, but depending on the speed of the oscillation only sees the shakes in one given direction.

 

To fix this, either disable FSX turbulence, or use ActiveSky Next. (yes I was very specific. No, other products don't do it well enough, even ActiveSky 2012, Rex etc).

 

Another issue is when the FSX program registry becomes corrupted. Default and various other products don't have a true "IRS" system, so they just use the FSX GPS or similar type of thing to figure out where they are. The PMDG 747 and MD11 however use their own IRS system which checks the FSX magnetic heading, and a calculation of all movements since IRS alignment to check where they are (all movements, even the silly turbulence as above). The issue is nearly 100% reproducable by having a correct registry (MD11/747 flying perfect centrelines alligned) then installing an FS9 afcad file or airport bgl with runway or navaid data in it. MD11/747 will now fly offset heading which is equal and opposite to the largest Magnetic Variation that you fly over in a single sim session. If you fly the atlantic from East Coast USA to UK then you will have about 13° offset. If you fly down to Antarctica past S65° then you will be looking at near 80° offset.

 

Uninstalling the FS9 files won't restore the registry, only the Flight1 registry repair will.

Flight1 Registry repair tool can be downloaded from http://www.flight1.com/view.asp?page=library (4th one down)

From another thread, user did not have the flight director engaged. Can't hurt to check :)