His behaviour is perfectly normal from a physiological point of view. Many patients after coming to the ER for something traumatic or stressful will toss their cookies once the treatment is over. Right down my leg if I'm not watching.
In the case of your student, he has anxiety during his flight, and then as he turns base, his subconscious tell his guts, "We're home safe soon boys, time to clean house!" and up it comes.
It sounds like torture, but encourage the kid to just keep flying over and over. Let it happen. Laugh about it. Like any other stimulus in life, soon we become accustomed to it and stop reacting as if it were the first time (no marriage jokes please).
Most important message to instill in this kid is that he is normal--his guts are hard-wired to clean house when he's stressed, and sooner or later, it will stop.
Yet another analogy is kids who throw up Christmas morning while waiting to open their presents... too much excitement!
Or my dog, who, no matter how long the car ride, throws up 10 seconds before arriving at any destination... right down my leg.
All the best.