On 21 October 2009 an Airbus 320-200 being operated by Northwest Airlines on a scheduled passenger flight from San Diego to Minneapolis-St Paul with the Captain as PF overflew its destination at cruise level in VMC at night by more than 100 nm after the two pilots had become distracted in conversation and lost situational awareness. They failed to maintain radio communications with a series of successive ATC units for well over an hour. After a routine inquiry from the cabin crew as to the expected arrival time, the flight crew realised what had happened and re-established ATC contact after which the flight was completed without further incident.