Over New York City in 1953, Eastern Airlines Flight 8610, a commercial flight, had a near miss with Air Force Flight 8610, a Lockheed C-121 Constellation known as Columbine II, while the latter was carrying President Eisenhower. This prompted the adoption of the unique call sign Air Force One, to be used whenever the president is on board any US Air Force aircraft. Columbine II is the only presidential aircraft to have ever been sold to the public and is the only remaining presidential aircraft left unrestored and not on public display.