Engle was selected as a NASA astronaut in 1966 and trained during the Apollo era. He was originally assigned as Lunar Module Pilot for Apollo 17, but NASA replaced him with geologist Harrison Schmitt so the final lunar landing would include a professional scientist. That decision kept Engle from walking on the Moon, but it also placed him among the most visible astronauts affected by Apollo's shrinking mission schedule.

Engle became a central pilot in the early Shuttle program. He commanded Space Shuttle Enterprise Approach and Landing Tests, then commanded STS-2, the second orbital Shuttle flight and the first reuse of a crewed orbital spacecraft. He later commanded STS-51I, a satellite repair and deployment mission. His career made him one of the rare people to manually fly both the X-15 and the Space Shuttle.

Engle's background fit the broader pattern of the early astronaut corps: technical training, operational discipline, and a career built around difficult work before spaceflight. His formal education included University of Kansas (B.S. Aeronautical Engineering, 1955). His service background is recorded as Major General, Air National Guard. His personal record also sits alongside a family life recorded as two marriages, two children and one stepchild, a reminder that these careers unfolded within ordinary lives as well as national history.