I suspect that on 24 hour patrol flights they are up and about, walking around reasonably often. I don't have any specific evidence, but it does seem reasonable that someone in a cramped corporate jet seat for 6 hours or more, without the opportunity to walk around because the small cabin is full of punters, might be at increased risk of DVT. Personally, I would consider taking aspirin, low dose, but it's a personal thing.
As you know, FD, if everything we did in general practice was evidence-based, we wouldn't be doing very much!
QDM