CACHE, Okla. (AP) _ A twin-engine Army aircraft on a routine maintenance test flight crashed Wednesday in southwestern Oklahoma, killing all three people aboard, military officials said.

Rick Brink, Army spokesman at Fort Sill, said the T-42 aircraft crashed about 1:50 p.m. four miles south of Cache. The plane had taken off from Fort Sill's Henry Post Airfield about a half-hour earlier to begin the test flight, he said.

He described the T-42 as a small aircraft that normally carries two passengers and two pilots.

Brink identified the dead as William T. Lamb of Lawton, the pilot; and passengers Terry M. Miller and Farrell V. Walker, both of Apache. He said all three were employed by Doss Aviation Inc., a civilian contractor that does aircraft maintenance work at Fort Sill.

''You could hear it hitting, it was kind of like a thud, like a bucket of sand hitting the ground,'' said farmer Dennis Haxton, who was about 350 yards from the crash.

''Then there was an explosion and then black smoke broiled up to flames, and then two minutes later there was another explosion,'' Haxton said.

Authorities were notified when flight controllers lost radar contact with the plane, and military authorities immediately were dispatched to the scene, he said.

The military will investigate the cause of the crash. ''At this time we can't speculate,'' Brink said.