PMDG 777F Frankfurt to Dubai - I had some additional contrails under my wings accompany my flight the entire route as per pic below:

 

 

Any ideas what may be causing this?

I had this problem occasionally with the 747 and it had something to do with if ur departure airport was raining. Can't remember what it was exactly but could never solve the issue

 

Hope someone else can chime in and help u

Same issue with me on the 747-400 with rainy weather departure.

I don't think this has anything to do with PMDG aircraft, if I remember correctly - its another one of those bugs in FSX. It happens when its raining. 

I have this same issue with the:

JS41, NGX, 747, MD11, 777, LDS 767, Realair Beechcraft Duke BE60, Carenado Beechcraft King Air BE90, yadda yoo etc etc.

 

It happens if it was raining at your departure airport.

 

I'm told there's some effects file you can remove and it will stop showing. however it will stop that effect when you are on wet ground too. and it will stop for every aircraft.

 

Again, PMDG can't fix Microsoft's mistakes. I sometimes think I'll find out how to remove that effect but never get the time ... one day...

I too experienced it. FSX bug.

If I recall it was raining on my departure at EDDF. More than likely an FSX bug. Thanks fellas.

This is indeed FSX bug, not sure where I saw that but probably in the PMDG 777 Introduction PDF.