When Should Cast Be Removed After Rhinoplasty?

I tend to leave the cast in place for 6 or 7 days post-op.
As for flying, remember that the cabin is a very dry place, so I recommend the frequent use of a saline (salt water) nasal spray throughout the flight (most bottles are way less than the 3 oz. limit imposed by the TSA). If the flight's longer than about two hours, I also recommend getting up and walking the aisle a few times to minimize the risk of deep vein thrombosis (clots in the deep veins of the legs). But flying after a week should be fine.
All the best,
--DCP

It’s not unusual for surgeons to use nasal splints following rhinoplasty surgery. These are used to hold the nasal bones in proper position. Nasal splints are typically left in place for about a week following this type of procedure. The majority of patients tolerate splint removal without difficulty
                Travel of any type following rhinoplasty can potentially complicate the post-operative course. In most cases, patients have recovered sufficiently to travel in about seven to ten days following surgery.

                Air travel often involves prolonged periods of immobilization and because of this, patients may be at risk for the development of blood clots in their extremities. These blood clots, known as DVT’s can potentially represent life threatening phenomenon when they occur.

                In addition, nasal congestion can be extremely uncomfortable when patients fly. For this reason, it’s appropriate to use nasal Afrin before taking off and landing. This maneuver will hopefully minimize nasal edema and relieve nasal congestion.

                To avoid complications, it’s important that these issues be discussed with your plastic surgeon. This will dramatically decrease the potential for complications. 

But yes, its there for the first week. Why? The usual answers are to protect your new nose and to reduce the post operative swelling. However if you look with a critical eye, a nasal cast doesn't really do either of these functions very well. Its too small to really protect and post operative swelling is more effectively treated by the taping beneath the cast. So the third reason is probably the best; its traditional. Surgeons are by and large conservatives. Surgeons do what they were trained to do, so if your surgeon's teather/mentor used a cast, then your surgeon will too. There's essentially no down-side, unless its a denver metalic cast and then because of its inflexability there's a fractional risk of ischemia and tissue loss. So lie back and relax. There more important issues to focus on.