When Mannix is flying the airplane during the search, they show the altimeter, which reads 14,500 feet. At the end of the scene with the airplane, the altimeter is shown again. This time it shows approximately 3,000 feet, and then nearly sea level. Since the Denver area is at an altitude of 5,000 feet above sea level, the altimeter was indicating between two and five thousand feet below ground level in the final airplane scene.