The Airbus A340 had been parked in a remote parking lot at the airport after landing Wednesday after a flight from Johannesburg. The plane, which had been Flight SA 207, had made one stop in Dakar, Senegal.
Authorities had yet to identify the man, whose body was found by a ground crew about 1:30 p.m. EST, WRC-TV, Washington, reported.
South African Airways representative Tlali Tlali said the airline regrets "any loss of human life and are deeply concerned about the suspicious circumstances surrounding this incident."
The body was turned over to the Fairfax County Medical Examiner.