He was one of twelve pilots who flew the North American X-15, an experimental spaceplane jointly operated by the United States Air Force and NASA.

During World War II he served as a Naval Aviator in the Pacific Theater, earning the Air Medal with two clusters, and a Presidential Unit Citation.

McKay worked for the National Advisory Committee for Aeronautics (NACA) and its successor, NASA, from February 8, 1951, until October 5, 1971, and specialized in high-speed flight research programs.

McKay wrote several technical papers, and was a member of the American Institute of Aeronautics and Astronautics, as well as the Society of Experimental Test Pilots.

Due to the excess speed and weight the aircraft experienced failures because of the increased dynamic loading which eventually led to its overturning.

While McKay appeared to suffer no permanent disabilities as a result of the crash, evidence was later found that he had sustained brain damage.

[3] Also, while he returned to piloting duties with NASA, recurring severe pain caused by the crash forced his early retirement.