I think my speeds were well within limits, but as I say, I will try slightly higher speeds. Odd, even if that were the cause, that the APs would shut off as a result though!Will try another flight when I can and report back.Thanks,Martin

The AP will definitely trip if speeds are outside tolerances. Not sure if you should be trying higher or lower speeds... you haven't provided much info.

Martin, Dan,Don't fly the 737 myself. Reading the discussion, I think the suggestion made by Mats, still remains unanswered.So , Martin, suggest trying this first (NO Active Sky AND Clear FS wheather) before moving to non-standard speeds or whatever other solutions....Regards,Harry

I will certainly try with all weather 'off', but it is not always possible to reproduce the error, as I noted above, (though it has happened several times at different locations), so may be some time before I can say what's happened.Thanks again for the support!Martin

It's very hard to troubleshoot this as when rerunning an ILS approach the panel state is not saved. I did try coming in too slow and sure enough, the plane stalls - with no sudden elevator shaking or APs switching themselves off. So it's not simply a question of airspeed.Will continue experimenting in different weather settings. Flew EGNX to EHAM yesterday with weather clear and no Active Sky - landed fine. But that proves nothing yet as the problem doesn't occur every time anyway. I'll double check my AS6 options too - perhaps something there. (Though if so, why are only the PMDG 737s affected?).M.

The only time I ever encountered your situation was with Wake T checked on by mistake in AS.The only other thing I can think of is make sure you have the latest FSUIPC. If you do then roll back to your previous version if that was working for you.Maybe that will work for ya.

I have always had Wake Turbulence unchecked in AS, but sure enough it has somehow become checked since I last checked, (er, looked!), so I've switched it off again. I must go through the AS options again - looks as if there have been some alterations (I suppose due to something I have done, but I can't think what! I haven't altered them purposely: ain't it always the case with PCs!).The last few times I had this problem it was at quiet airports with traffic at 0%, so I doubted that Wake T would be the cause, but who knows? (Even so, why would WT turn off the APs?).If I still get the problem after going through Active Sky options again, I'll post back!Thanks everyone for all the comments,Martin

(Yes, BTW, have latest FSUIPC file)