The Northwest Pilots who overshot a Minnesota runway by 150 miles last week told investigators they were using their personal laptops in the cockpit, a violation of company policy, according to a National Transportation Safety Board advisory.

The two pilots, interviewed separately on Sunday, told investigators they lost track of time when they used their laptops while in a “concentrated period of discussion” about the new monthly crew flight scheduling system.

The system reportedly changed after the Northwest-Delta merger.

The pilots told NTSB officials that they had not been monitoring the airplane or calls from Air Traffic Control at that time, according to the report.

Both pilots said they heard conversation on the radio, but failed to notice messages that were sent by dispatchers. It wasn’t until a flight attendant called the pilots about five minutes before the flight was scheduled to land that they realized they had passed the airport, according to the report.

Fighters from two North American Aerospace Defense Command sites were put on alert for the plane when it was not responding to radio calls from the Federal Aviation Administration, NORAD reported.

The alert was called off once the FAA re-established communications with the pilots, according to NORAD.

Both pilots told investigators that they did not fall asleep nor have a heated argument, according to the advisory.

The Wall Street Journal reported that additional factors also may have contributed to protracted radio silence.

NTSB spokesman Keith Holloway said investigators interviewed the pilot and co-pilot in person in Minneapolis.

The agency also interviewed the three flight attendants on Monday, Fox News has learned.

Northwest Airlines is cooperating and conducting its own internal investigation, said 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 Airbus A320 Minneapolis-bound flight, which later turned around and landed safely. There were 144 passengers on the flight.

The NTSB said it will continue its investigation.

Click here to read more from The Wall Street Journal.

The Associated Press contributed to this report.