The US National Transportation Safety Board says pilot distraction was the major factor in a highly publicised Airbus A320 overflight of Minneapolis by Northwest pilots late last year, but the agency's investigation also showed ambiguity in certain air traffic control procedures.
On 21 October 2009 Flight 188 overflew Minneapolis by more than 180km (100nm), with the pilots failing to maintain radio communications for about 1h 17min.
"The investigation found that the pilots had become engaged in a conversation dealing with the process by which pilots request flight schedules, and during the conversation each was using his personal laptop computer, contrary to company policy," says the NTSB. Northwest and Delta Air Lines merged in 2008, and received a single operating certificate in December 2009.
A factor in the delay by controllers of performing necessary actions required under lost communications procedures is a lack of national requirements in the USA for recording air traffic control instructions when automated flight tracking systems are in use, says the NTSB. These are to ensure an aircraft has checked in on an assigned frequency or to direct a frequency switch.
The NTSB also says that since most episodes of non-radio communication are of short duration, it found that "controllers and managers may have become complacent in completing necessary NORDO [no radio communications] actions and required notifications in a timely manner".
The issues raised by the board are the lack of standard procedures for identifying flightcrew-ATC communications in ATC facilities that use automated flight tracking systems, and a lack of standard phraseology to identify the emergency nature of ATC radio transmissions.