For one hour and 18 minutes Wednesday night the pilots -- flying at 37,000 feet above sea level between San Diego and Minneapolis -- were radio silent as air traffic controllers at times tried to reach the cockpit.
As the event unfolded, concern was high among air traffic controllers, who repeatedly attempted to establish contact during the incident, 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, a method that the union said ultimately proved successful.
Federal counterterrorism agencies treated the stray jetliner as a serious threat. Fighter jets were placed on alert, though not put in the sky.
In separate interviews with the NTSB, Cheney and Cole told investigators they were in a "concentrated period of discussion" over a new monthly crew flight scheduling system in place as a result of the merger of Delta and Northwest. Both accessed and used his personal laptop computer while they discussed the airline crew flight scheduling procedure. Cole, who was more familiar with the procedure, was providing instruction to Cheney, the NTSB said.
The pilots said they lost track of time and were using cockpit speakers to listen to radio communications, not their headsets.
Initially, there was speculation that the pilots had fallen asleep in the cockpit. Both pilots dismissed that, saying there were not fatigued. Each had commuted to the flight, but they had a 19-hour layover in San Diego before arriving at work. They both told investigators that they did not doze during the flight and there was no heated argument.
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.
Capt. Cheney, 53, was hired in 1985 and has about 20,000 hours of total flight time including about 10,000 hours in an Airbus A-320, the plane he was flying the night in question. About 7,000 of those hours were as pilot in command of the A-320.
First Officer Cole, 54, was hired in 1997. His total flight time is about 11,000 hours and he has about 5,000 hours on the A-320.
With reporting from ABC News' Lisa Stark, from National AeroSpace Training and Research Center, and Matt Hosford.