Hi Remy.

Is this only happening with the Captain Sim 777, or is it happening with all the jet aircraft?

I had this strange effect with the contrails happen to me a long time ago (it was happening to all the jets). I can't remember how exactly I stopped it.

It looks like you are something like Orbx FTX scenery, so you could try disabling it, test the 777 to see if it's okay, then re-enable the scenery. I usually disable the scenery in the Settings > Scenery Library, and uncheck the boxes for the scenery. This is done from the Start Screen, so from within the FSX, you go Menu > World > Scenery Library, and uncheck the boxes for the scenery. Do not remove them, or change the order that they are used, otherwise you will need to reinstall/repair them.

Over the last year or so, I haven't been using any addon scenery, so I don't know if I would have this problem if I was using them. :-/