ALPINE, Tex. — An airplane serving as an ambulance crashed shortly after taking off from a West Texas airport early Sunday, killing all five people on board, officials said. The crash occurred around 12:15 a.m. about a mile east of Alpine-Casparis Municipal Airport, which is 200 miles southeast of El Paso. The plane, a twin-engine Cessna 421, was en route to Midland when it crashed in a field, according to the Federal Aviation Administration. The aircraft was transporting a patient and his wife, the Texas Department of Public Safety said. It identified the couple as Guy Richard Folger, 78, and Mary Folger, 59, of Alpine. Also on board were two flight nurses, Sharon Falkener, 49, of Fort Davis, and Tracy Chambers, 42, of Alpine, and the pilot, Ted Caffarel, 59, of Beaumont. The F.A.A. listed the aircraft as registered to O’Hara Flying Service II LP of Amarillo. The National Transportation Safety Board will lead an investigation into the crash, an F.A.A. spokeswoman said.