CIA test pilot Ken Collins didn't know exactly where he was when his A-12 spy plane suddenly "didn't feel right," only that he was somewhere west of Salt Lake City.

Collins, followed by an Air Force chase plane, had just turned south on May 24, 1963, during a test flight of the twin-engine jet. The top-secret A-12 was the most advanced aircraft of its time. In fact, new technologies for engines, composite materials, lubricants and metallurgy were racing to keep up with the plane's goal to evade radar while cruising at higher than 85,000 feet and more than triple the speed of sound.

"It was an amazing aircraft, but everything had to work perfectly," recalls Collins, a retired Air Force colonel and veteran of the Korean, Vietnam and Cold wars who lives in Woodland Hills, Calif. "It was a very complex plane, and we had very complex problems. And if something went wrong, it went wrong in a hurry."

But this test flight had been uneventful, Collins recalls. Just before noon, he turned south to return to the plane's base at the CIA's top-secret Area 51 north of Las Vegas. At 25,000 to 30,000 feet over the Utah-Nevada border, the A-12 entered clouds, and that's when the pilot lost sight of the chase plane, according to recently declassified documents.

Something had subtly changed in the A-12's handling.

"The airplane just didn't feel right," Collins says. The readings on the dozens of dials and readouts in the cockpit looked benign, but something seemed wrong.

The experienced test pilot's instincts were right. Investigators later would learn that the heating element on the pitot tube that feeds data to the instruments had failed, and the tube had iced up.

What happened in the next few minutes would lead to a cover-up that would ultimately ignite the imagination of an aviation historian before finally becoming the subject of new National Geographic Channel documentary on the mysteries of Area 51.

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