Is there a doctor on board? Surprisingly often, there is, in half of in-flight medical emergencies , and sick airline passengers almost always survive, a new study finds. The research is the largest look yet at what happens to people who develop a medical problem on a commercial flight , about 44,000 of the 2.75 billion passengers worldwide each year, researchers estimate. Most cases don't require diverting a plane as the study's leader, Dr. Christian Martin-Gill, advised a pilot to do two years. He works for MD-STAT, a service at the University of Pittsburgh Medical Center that advises about 20 major airlines on how to handle in-flight emergencies. Another large service is based in Phoenix.