Safety investigators are highly skilled at solving the mystery of plane crashes. But with Northwest Flight 118, which landed safely, they are tackling a different puzzle: What went on in the cockpit to cause it to fly for 500 miles without radio contact and well beyond its destination?
On Friday, investigators sought to explain why the two pilots of the Northwest flight, bound from San Diego to Minneapolis, did not begin a normal descent when they should have on Wednesday night.
The pilots, Capt. Timothy Cheney, 53, of Gig Harbor, Wash., and First Officer Richard Cole, 54, of Salem, Ore., said they had been involved in a heated discussion about airline policy and lost track of where they were.
Skepticism about the pilots' explanation resounded throughout airline and aviation safety circles, which wondered whether they had fallen asleep. The Federal Aviation Administration prohibits pilots from snoozing in the cockpit.
"What did they say? What went on? What was the subject of discussion — or weren't they talking?" asked James Oberstar, the veteran Minnesota Democratic congressman and chairman of the House Committee on Transportation and Infrastrucure.
Cole denied the two had been asleep. "I can assure you none of us was asleep," he told ABC News on Friday night. He declined to comment further but added, "I am not doing very good."
When the pilots did not respond to repeated radio calls, the FAA notified the military, which put Air National Guard fighter jets on alert at two locations, although none took to the air.
Two aviation officials from separate agencies said that Wednesday's flight was the first of the day for both pilots, who had had a layover of about 17 hours.
Instead of landing the Airbus A320, with 144 passengers and three flight attendants aboard, the pilots flew past Minneapolis to the skies above Eau Claire, Wis., despite repeated radio calls from controllers and other pilots in the area as well as e-mail messages from the airline's dispatchers. Finally, when the plane was 110 miles past the airport, they responded, according to a report from the Minneapolis St. Paul Airport Police Department.
The pilots were finally alerted to their situation when a flight attendant called on an intercom from the cabin. Most of the passengers didn't seem to realize anything was wrong.
The pilots have been suspended by Delta Air Lines, which merged with Northwest last year and operates its flights, pending the outcome of investigations.
The pilots passed breath analysis tests to check for alcohol, the police report said. When the plane landed, the report said, Cheney turned to waiting officers and gave a "two thumbs-up" sign through the cockpit window.
Officials at the National Transportation Safety Board said they planned to listen to the plane's cockpit voice recorder on Friday afternoon, but that might not provide any answers. The recorder, which runs continuously throughout a flight, has only 30 minutes of sound at any one time, and records over itself. The officials said they would interview the pilots over the weekend and would have something to report as early as Monday.
Aviation officials said that the radio communication with the plane ceased after 6:46 p.m., central time, and did not resume until 8:14 p.m., a gap of 88 minutes.
Several airline pilots told the Los Angeles Times that cockpit catnaps happen and that they are surprised napping mishaps haven't happened more often, considering longer pilot work schedules and aviation advances that make planes easier to fly.
"Pilots on occasion do take controlled naps," Barry Schiff, an aviation safety consultant and retired pilot, told the newspaper.
Information from the Los Angeles Times was used in this report.