Federal investigators were interviewing the crew of the Northwest Airlines flight that overshot the Minneapolis airport by 150 miles.
National Transportation Safety Board spokesman Keith Holloway said investigators will interview the pilot and co-pilot in person on Sunday in Minneapolis. He would not provide additional details, but did say the NTSB will not comment on the substance of the interviews until Monday at the earliest.
Northwest Airlines is cooperating and doing its own internal investigation, says Chris Kelly, a spokesman for Northwest Airlines' parent company, Delta Air Lines Inc.
Air traffic controllers tried for more than an hour Wednesday night to contact the Minneapolis-bound flight, which later turned around and landed safely. First officer Richard Cole has said he and the captain were not sleeping or arguing in the cockpit, but hasn't explained their lapse in response and the detour.
"It was not a serious event, from a safety issue," pilot Richard Cole said late Friday in front of his Salem, Ore., home. "I would tell you more, but I've already told you way too much."
Officials on the ground alerted National Guard jets to prepare to chase the airliner, though none of the military planes left the runway.
The jet with 144 passengers aboard was being closely monitored by senior White House officials, White House spokesman Nick Shapiro told The Associated Press on Saturday. He didn't say if President Barack Obama was informed.
Many aviation safety experts and pilots say the most likely explanation is that the pilots fell asleep along their route from San Diego. NTSB spokesman Keith Holloway said fatigue and cockpit distraction are factors that will be looked into.
"We were not asleep; we were not having an argument; we were not having a fight," Cole said.
He would not discuss why it took so long for the pilots to respond to radio calls, "but I can tell you that airplanes lose contact with the ground people all the time. It happens. Sometimes they get together right away; sometimes it takes awhile before one or the other notices that they are not in contact."
Passed alcohol breath tests
The Minneapolis Star Tribune, citing an internal Northwest document it said was described to the newspaper, reported that Cheney and Cole began what was to be a five-day flying stint Tuesday with a flight from Minneapolis to San Diego. The newspaper said the pair had a 19-hour layover before Wednesday's return flight.
A police report released Friday said the pilots passed breathalyzer tests and were apologetic after the flight. The report also said that the crew indicated they had been having a heated discussion about airline policy.
But aviation safety experts and other pilots were deeply skeptical they could have become so distracted by shop talk that they forgot to land an airplane carrying 144 passengers. The most likely possibility, they said, is that the pilots simply fell asleep somewhere along their route from San Diego.
"It certainly is a plausible explanation," said Bill Voss, president of the Flight Safety Foundation in Alexandria, Va.
Unfortunately, the cockpit voice recorder may not tell the tale.
New recorders retain as much as two hours of cockpit conversation and other noise, but the older model aboard Northwest's Flight 188 includes just the last 30 minutes — only the very end of Wednesday night's flight after the pilots realized their error over Wisconsin and were heading back to Minneapolis.
Suspended during inquiry
Cheney and Cole have been suspended and are to be interviewed by National Transportation Safety Board investigators next week. The airline, acquired last year by Delta Air Lines, is also investigating. Messages left at Cheney's home were not returned.
FAA spokesman Tony Molinaro said in general, an unsafe condition created by a pilot could lead to the suspension of the person's pilot license and possibly a civil penalty.
With worries about terrorists still high, even after contact was re-established, air traffic controllers asked the crew to prove who they were by executing turns.
"Controllers have a heightened sense of vigilance when we're not able to talk to an aircraft. That's the reality post-9/11," said Doug Church, a spokesman for the National Air Traffic Controllers Association.
NTSB spokesman Keith Holloway said fatigue and cockpit distraction will be looked into. The plane's flight recorders were brought to the board's Washington headquarters.
The pilots were finally alerted to their situation when a flight attendant called on an intercom from the cabin.
Voss said a special concern was that the many safety checks built into the aviation system to prevent incidents like this one — or to correct them quickly — apparently were ineffective until the very end. Not only couldn't air traffic controllers and other pilots raise the Northwest pilots for an hour, but the airline's dispatcher should have been trying to reach them as well. The three flight attendants onboard should have questioned why there were no preparations for landing being made. Brightly lit cockpit displays should have warned the pilots it was time to land.
"It's probably something you would say never would happen if this hadn't just happened," Voss said.