Two distracted United States pilots were using laptop computers against company rules when they overshot their destination by 240km, according to federal investigators.
The experienced pilots, aged 53 and 54, were questioned for five hours by National Transportation Safety Board officials seeking an explanation to the unusual mistake, AFP reports.
The Northwest Airline Airbus A320 was flying from San Diego, California, with 147 passengers and five crew when it grossly overflew its destination of Minneapolis on 21 October.
A flight attendant had to call the pilots on the intercom to alert them to the situation.
The pilots, with no record of accidents, incidents, violations or medical problems, told NTSB they lost track of time.
They ignored calls from their company - Delta Airline, which owns Northwest - and were using their laptops against company rules while discussing new work schedules under the company merger.
The pilots were oblivious to what was happening when, five minutes before their scheduled landing, a flight attendant asked them when the plane would land.
Only then did the pilots realise their mistake and contact air traffic control in Minneapolis to redirect their flight.
Normally, landing procedures in a commercial flight begin at least 200km before the destination, NTSB experts said.
The pilots' explanation of the incident has been confirmed by preliminary data from a half-hour recording from the plane's cockpit voice recorder.
Passengers on the flight were unaware of what was happening, although some witnesses later said they thought the flight was taking longer than usual.