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 Visual Meteorological Conditions (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.
The investigation was carried out by the National Transportation Safety Board (USA) (NTSB) who established that the flight crew had become engrossed in conversation about rostering and had each been using their personal laptop computers, contrary to Company policy. Following an acknowledgement of a frequency change to the next en route centre during the cruise at FL 370 about two hours after departure in the vicinity of sunset, the flight crew were found to have flown through six successive ATC sectors before contact was re-established. The Investigation concluded that the incident had highlighted the effect of a lack of national requirements for recording ATC instructions when using automated flight tracking systems, such as directing an aircraft to switch frequencies or indicating that an aircraft has checked in on an assigned frequency. In addition, it was considered that because radio communication failure events of short duration are not uncommon, controllers and ATC managers may have become complacent in their response.
The Investigation found that ATC procedures for both flight handover between sectors and for response to loss of radio contact with an aircraft - described as NORDO status in the USA - were inadequate. Upon request from the NTSB during the course of the investigation, the FAA advised their corrective action in respect of improving awareness of the communication status of aircraft at ATC Units, but this was not considered sufficient.
The results of the NTSB Investigation were published on 18 March 2010 and two Safety Recommendations arising from it were made to the Federal Aviation Administration (FAA) on the same day by letter (See: Further Reading). See the Full Report which includes the Probable Cause Statement and Recommendations.
The two Recommendations made were as follows:
- Establish and implement standard procedures to document and share control information, such as frequency changes, contact with pilots, and the confirmation of the receipt of weather information, at air traffic control facilities that do not currently have such a procedure. These procedures should provide visual communication of at least the control information that would be communicated by the marking and posting of paper flight-progress strips described in Federal Aviation Administration Order 7110.65, “Air Traffic Control.” (Recommendation A-10-42)
- Require air traffic controllers to use standard phraseology, such as “on guard,” to verbally identify transmissions over emergency frequencies as emergencies. (Recommendation A-10-43)
It should be noted that in respect of the reference to R/T phraseology in Recommendation A-10-43, the phrase ‘on guard’ is not an internationally designated or accepted standard expression. The NTSB say (in respect of the US) that “although not required to, pilots and controllers have historically used the phrase ‘on guard’ when beginning transmissions on designated emergency frequencies.”