The Air Force and the Navy have combined research into a perplexing problem that may have vexed both services in the skies. The U.S. Air Force School of Aerospace Medicine and the Naval Medical Research Unit, next door to each other at Wright-Patterson, have linked research for hypoxia — incidents that may have caused a lack of oxygen to reach pilots during some flights in the Air Force’s F-22 Raptor stealth fighter and the Navy’s F-18, military leaders said. “We had what we believe was a common issue,” said Capt. Rita Simmons, executive officer of the Naval Medical Research Unit....