Due my years of travel I am unfortunate enough to have had DVT twice, fortunately both times was in each calf muscle. And whilst it’s still a very dangerous condition if you have it below the knee there is less chance of it moving. It’s very painful, takes weeks of daily visits to the hospital to have your bloods checked, self-injecting warfarin for a couple of weeks, and then months of warfarin tablets.
Even now years later I get really bad cramp in the calf muscles which are solid as a brick due the damage to them and have to take aspirin daily and double dose on travel days.
Whatever you can do to avoid it do, it’s not just planes, just sitting at your office desk a long car or train journey are all factors. Be careful.