One of the two Northwest Airlines pilots who were out of contact with air traffic controllers for more than an hour Wednesday while they overshot their destination denies suggestions that they fell asleep.
"I can assure you none of us was asleep," First Officer Richard I. Cole told ABC News.
He declined to comment further but said, "I am not doing very good."
This evening, the Federal Aviation Administration released a brief statement suggesting the pilots on the San Diego-to-Minneapolis flight could face serious consequences as the agency investigates.
"The FAA has sent letters of investigation to the two pilots involved in the recent Northwest Airlines overflight of Minneapolis," the statement said. "Depending on the outcome of our investigation, this action could lead to emergency suspension or revocation" of their licenses.
Cole and fellow pilot Timothy B. Cheney told the FBI and airport police they lost track of time and got distracted because they were in a heated discussion over airline policy, the FAA has said. The pilots told police "they had become involved in conversation and had not heard radio communications."
The pilots of the Airbus A320 were out of contact with air traffic controllers who frantically tried to reach the plane for 1 hour and 18 minutes.
The pilots -- who stayed at 37,000 feet and overshot the airport by 150 miles -- were finally reached at 8:14 p.m., but the jet with 147 passengers did not land at Minneapolis-Saint Paul International Airport until 9:05 p.m.
The cockpit voice recorder on the flight is only a 30-minute recorder, resetting on a loop after that period, according to the National Transportation Safety Board. That means that unless the pilots stopped the recorder, the only sounds captured from the flight would be the last half hour, when the pilots were back in communications with air traffic controllers.
Newer flight recorders tape two hours of sounds before resetting.
"From the point of course reversal to touchdown was about 50 minutes," said Daniel Baker, founder and CEO of flight-tracking company FlightAware.com.
Since Delta and Northwest merged a year ago, many pilots have been angered over job seniority and the routes they fly, perhaps a factor in a cockpit discussion.
Airport police who met the plane at the plane at the gate asked the pilots to submit to a alcohol breath test. Cheney and Cole both voluntarily agreed and the tests showed no traces of alcohol, according to the police report.
It appears that there were no bells or whistles or any other audible sound to alert the pilots that they had passed their last flight marker, so-called "way points."
Instead, there would be a message on screens that sit on the pedestal between the two pilots. That message would have said "flight plan discontinuity."
Federal counterterrorism agencies treated the stray jetliner as a serious threat. Fighter jets were placed on alert, though not put in the sky.
Authorities began to immediately look at the flight manifest and crew and checked to see if there were air marshals onboard. The National Counterterrorism Center was notified and the Minneapolis Joint Terrorism Task Force was put on notice.
"As part of our procedures for events of this nature TSA protocol included checking possible screening anomalies from the departing airport, checking to see if Federal Air Marshals were onboard, notification to the airline, as well [Transportation Security Administration] and [Department of Homeland Security] leadership," Sterling Payne, TSA deputy assistant administrator said in a statement.
"This is an extraordinary, unusual case," William Voss of the Flight Safety Foundation told "Good Morning America." "I can think of very few times in recent history where we have seen this type of really extreme overflight."
One of the many possibilities that investigators will look at is whether one or both pilots were sleeping.
"This is unprecedented ... in terms of being so unaware of where you are and what you're doing," former pilot and ABC News aviation consultant John Nance said. "This is virtually off the charts. The far more likely explanation is they fell asleep."
Although Nance said it is common for pilots to fall asleep on long trips, the pilots' story may hold truth, former National Transportation Safety Board investigator Greg Feith told "Good Morning America."
It's possible the pilots did not hear instructions to update their frequency and never heard the air traffic controllers' repeated calls to them, he said.
"You have to tune your ear to the call sign," Feith said. "If you're in a heated discussion, if you're distracted, you can miss that call sign."
As the event unfolded, concern rose among air traffic controllers who repeatedly attempted to establish contact, using multiple methods, the air traffic controllers union told ABC News.
Eventually, controllers asked other planes in the air to attempt to contact the Northwest plane, which proved successful, the union said.
"Regardless of what happened in that cockpit, this incident highlights some of the policy gaps that must be filled to create an air travel industry that is fair to pilots and as safe as possible for consumers," said Anne Banas, executive editor of SmarterTravel.com. "Current pilot fatigue rules are outdated and have no real relevance to the modern aviation industry -- they place an unfair burden on pilots and crew, and put passengers at unnecessary risk. Plus, the simple fact that aircrafts are carrying older cockpit recorders is very surprising, and should be remedied."
NTSB Plans to Interview Pilots Who Were Allegedly Asleep at the Controls
The NTSB plans to interview the crew and is reviewing the cockpit voice recorder and flight data recorder of the flight, Northwest 188 from San Diego to Minneapolis. The NTSB will be investigating whether the pilots fell asleep, along with all other possibilities.
"There wasn't any problem on board -- nothing," Andrea Allmon of San Diego told ABC affiliate KSTP Thursday. "We landed, everyone got ready to get off the plane and suddenly police were getting on the plane and telling us to sit down. They went into the cockpit, looked around and then told everyone to get off the plane."
Early in 2008, the two pilots of a go! Airlines flight from Honolulu to Hilo, Hawaii fell asleep for at least 18 minutes while in the air. The plane flew past the airport and out to sea before air traffic controllers finally were able to reach the pilots, who turned the plane around. The captain later was diagnosed with sleep apnea.
Delta Airlines, which now owns Northwest, said in a statement that the "safety of our passengers and crew is our top priority."
"We are cooperating with the FAA and NTSB in their investigation, as well as conducting our own internal investigation," Delta said in the statement. "The pilots have been relieved from active flying pending the completion of these investigations."
Asked how many years of service the pilots have and how many hours they were into their shift, a Delta spokesman said, "We are not sharing as that is all part of the investigation."
This is the second instance in just days of a Delta flight crew having an apparent safety lapse.
Monday at 6:05 a.m., Delta flight 60 from Rio de Janeiro to Atlanta landed on a taxiway instead of the parallel runway where it was supposed to touch down. There were no injuries to any of the 182 passengers or 11 crew members on the flight.
ABC News' Matt Hosford, Lisa Stark and Pierre Thomas contributed to this report.