Hi supernova,
There must be some other factors than just the 747, because I don't see this when at KSEA, using the 747-400 as an AI aircraft.
It could be tied to a rendering setting, or it could be the airport. If it doesn't have hand drawn taxi routes, the AI aircraft may just be driving like an idiot, and making a lot of smoke from braking constantly or something along those lines.
ETA: Apologies, I just realized I was using a preview build of 11.10 with a lot of fixes in it, so it's also possible we've already fixed the issue too!