In 1970, he was reassigned to the 27th Tactical Fighter Wing at Cannon Air Force Base to fly F-100 and F-111 aircraft. He participated in the operational test and evaluation of the weapons system of the F-111D aircraft. Grabe attended the USAF Test Pilot School in 1974 and, upon graduating in 1975, was assigned to the Air Force Flight Test Center as a test pilot for the A-7 and F-111. He was the program manager and chief project pilot for the Air Force's digital flight control system for tactical fighters (DIGITAC) evaluation. He later served as an exchange test pilot with the Royal Air Force at Boscombe Down, United Kingdom, from 1976 to 1979. During this tour of duty, he served as the chief project pilot for the Royal Air Force Harrier and the Royal Navy Sea Harrier. He was an instructor at the USAF Test Pilot School at Edwards Air Force Base, California, when advised of his selection by NASA.