The US airline crew that overshot their destination by 100 miles had no idea anything was wrong until one of the cabin crew told them, investigation papers released today reveal.

They were unaware that they had flown their Airbus A320 with 144 passengers past the city of Minneapolis, that air traffic controllers and their airline's dispatchers had been struggling to reach them for more than an hour, or that the US military was at that moment readying fighter jets for an intercept mission.

Timothy Cheney, the captain of Northwest Airlines Flight 188, said he looked up from his laptop computer to discover there was no longer any flight information programmed into the plane's computer.

The plane had been out of radio contact for 77 minutes as it flew across a broad swathe of the US on October 21, raising national security concerns.

Capt. Cheney, 54, and First Officer Richard Cole, 54, told investigators they had taken out their laptops and were absorbed in working on a complicated crew scheduling programme that they were required to learn following Delta Air Lines' acquisition of Northwest a year earlier.

Flight attendant Barbara Logan told investigators from the National Transportation Safely Board she called the cockpit to find out when they would be landing but the flight crew hung up on her.