The opening credits show a Boeing 707 making a landing approach, then the shot cuts to the landing gear of a B-52 touching the runway.
When the Denver Fire Department truck pulls alongside he rear fuselage the vertical stabilizer appears to belong to a DC 6 or 7C v- a propeller driven airliner. Also, airport equipment should have been used instead of city, since they would be able to lay down foam or other aircraft related substances.