The incident raised fears of a possible hijacking
The two Northwest Airlines pilots whose plane overshot its destination by 150 miles on Wednesday say they were using their laptop computers.
The federal agency investigating the incident quoted the pilots as saying they had accessed their personal computers during the flight.
Contact with the Northwest Airlines jet was lost for more than an hour before it landed in Minneapolis.
The use of personal computers on the flight deck violates company policy.
The National Transportation Safety Board released a statement on Monday after interviewing the two pilots separately on Sunday for more than five hours.
The agency said both pilots denied speculation that they had been tired or fallen asleep during the flight.
They said they "had lost track of time" as they discussed a new crew flight scheduling system and accessed their personal computers at the same time.
They admitted that during their discussion, they did not monitor calls from air traffic controllers, nor did they notice messages sent by company dispatchers.
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They stated that they had been unaware of the plane's position until a flight attendant asked them about their estimated time of arrival five minutes prior to their scheduled landing.
It was only at this point, the captain said, that he became aware that his plane carrying 147 passengers from San Diego had overshot Minneapolis-St Paul International/Wold-Chamberlain Airport.
In total, the pilots were out of communication with air traffic controllers for more than an hour, sparking fears that their plane had been hijacked.
Fighter jets from the National Guard were put on alert to chase the airliner, although they did not take off.
Asked by air traffic control what was wrong, the pilots cited "cockpit distraction". They have been suspended.
The investigation by the National Transportation Safety Board continues, with the flight attendants scheduled to be interviewed later on Monday.