Just what happened on Northwest flight 188? Why did the plane overfly its destination, the Minneapolis airport, by 150 miles? Voice recorders may hold the answers the National Transportation Safety Board (NTSB) investigators are searching for. Meanwhile there is speculation the pilots fell asleep in the cockpit.
"I think they fell asleep," said Barry Schiff, an aviation safety consultant. "Most likely they did."
Sources tell ABC News the last radio contact with the plane occurred at 6:46 p.m. Central Time. Ten minutes later, at 6:56, Denver controllers tried to hand off the pilot to controllers in Minneapolis but got no response from the cockpit. It wasn't until more than an hour later that controllers and pilots reconnected. So much time had passed that F-16 fighter jets were prepared to shoot if ordered to do so. But 144 passengers aboard were unaware of the problem.
"The captain had come on and they said after some back and forth and bickering, we should be landing in 15 to 20 minutes," said Amy Kieffer, a passenger on the plane.
The pilots told NTSB investigators that they were in a heated discussion over airline policy and they lost situational awareness.
Friday, ABC News asked one of them if they were asleep. "There's a board next week. I'll tell you this, neither of us was asleep."
"It's possible that yes, they were in a heated discussion, but they would have had to been so involved for 15 minutes to a half an hour, and that's not likely. To lose track of where you are for that long is almost unheard of," said Schiff.
Minneapolis airport police said the pilots passed a breathalyzer test when they landed and that they were cooperative and apologetic.
Friday afternoon, some experts say whatever happened, the outcome is inexcusable and the fallout will be significant
"I would say that whether the pilots fell asleep or were distracted in conversation, they are in for a long stretch on the beach," said Schiff. "Possibly a license suspension as well."
The cockpit voice recorder may not be able to tell the whole story. Apparently it was set on a 30-minute loop, so the most it recorded was the last half-hour in the cockpit before landing.