I just downloaded Tom Ruths AMAZINGLY well modeled Airbus A300, and I took it out for a nice long range flight From Heathrow, to Kennedy Intl. Because it was such a long flight, and the long flight was pushing the range limits of the A300, I was crusing at only mach .65, at fl 380, in order to conserve as much fuel as possible. Well anyway, it started crusing fine, for the first few hours everything was perfect. But then once the fuel started dipping below 40% or 40,000 lbs the plane started ossilating up and down between 37,700 feet, and 38,300 feet. I tried taking off the autopilot, and leveling out at fl 380, and then turn it back on, and within seconds it was back to the ossilations. It seems that the trim is over sensitive, and because its so sensitive, the autopilot was majorly overcorrecting. Is there any ways I can fix this? Its a reallly beautiful aircraft otherwise.. like realllly beautiful.. it gives Payware a run for the money. (no pun intended) This is a borrowed SS showing just how amazing the virtual cockpit is.. (its Tom ruths' 717, but the A300 is just as well modeled, if not better) http://www.simviatio.../1298256610.jpg

Autopilot design is a difficult subject and sometimes the implementation in an add-on aircraft is not as good as it could be. In your case I would just recommend flying faster until the oscillation stops, and if it doesn't, disconnect the AP momentaily and stabilize the aircraft yourself, then reconnect the AP. In any case flying at .65M at FL380 translates to 202 KIAS which is way too slow and in the RW likely below the range-maximizing speed. Cheers, - jahman.

Sounds like a problem I've had in the past when CG has been out, or nearly out of limits - the autopilot just cant handle it, especially at high FLs. Did you check weight & balance before and after loading full fuel?