It does not matter if you want to have sex on a plane, on a hot air balloon or during skydiving as long as you keep the security rules. First of all, you need to know that it is not suggested to have sex on a public airplane. If you enter the restroom with your partner and you stay there for too long, the flight attendant can break the door and even let the pilot know about what you are doing, and you might be banned from flying if you are caught, since you can mean a possible threat. This is why sex in the air can be expensive. You should do it in private. So, you can either rent a jet, or a balloon, or you can also do it right in the air as soon as you have jumped out of the plane.
Obviously, there are not much security measures on a private jet, except that you should not be doing it while you are taking off or landing, and you need to buckle up if you pass through turbulence and if your flight attendant suggests you so.
A hot air balloon is slightly different. You only need to know that you either need to learn how to operate one, or not be bothered by a person who can. And since it is pretty easy to fall out if you do not do everything as told, which can lead to an imbalance of the basket.
Skydiving is a great choice because you can have sex on the plane already, especially if you get on board naked except for the parachute. The best to do it during a jump is if the penis is already in the pussy, any way, since it would be quite a challenge to insert it at 120mph. The most basic step is obviously that you should not forget is not to open the parachute in time.
Go ahead and try it when you can.