Investigation of Minneapolis Overflight Reveals Communication Shortcomings

Thu, Mar 25, 2010 — David Evans


In October 2009 Northwest flight 188 barreled through the night sky between San Diego and Minneapolis, its flight crew oblivious to repeated efforts to raise them on the radio. A call from air traffic controllers on an emergency frequency, and a text message from the airline’s operations center, failed to elicit a response.

The two pilots of the A320 twinjet were engaged in a vigorous discussion about crew scheduling, even to the point of opening their laptop computers to go over finer points of how pilots would bid for routes under the merger with Delta Air Lines. To be sure, at cruise altitude, 37,000 feet in this case, the crew was permitted to converse, but only on a “not to interfere” basis with flight duties. Nope, the pilots were oblivious to their primary duty, failing to make radio calls, failing to acknowledge radio calls, failing to notice the yellow blinking lights of an ACARS (Airborne Communications Addressing & Reporting System) text message from the airline. (See Aviation Safety Journal, ‘Pilots of Northwest Jet Facing Loss of Licenses’)

The airplane passed through five air traffic control sectors, out of radio contact for fully an hour and 17 minutes. The National Transportation Safety Board (NTSB) investigated the incident and recently released its report, which focused on the air traffic control lapses in the case.

The two pilots have since been fired and Delta indicated it will modify the ACARS system to include an aural alert for certain messages (presumably, an aural alert for the crew to respond to the radio will be among these select text messages).

The crew was broken out of its conversational distraction by a flight attendant, who inquired from the cabin via intercom when the airplane would be descending to the Minneapolis destination. The captain then looked at his multifunction control and display unit (MCDU) and saw there was no flight plan information depicted. Of course not; the airplane was scheduled to fly to Minneapolis and at this point was some 100 miles past the destination airport.


The realization in the cockpit was doubtless one of those “aww s—“ moments. The first officer noticed the ACARS message mutely illuminated, and immediately contacted air traffic control. The flight’s inordinately long NORDO (no radio communications) status was over. The airplane turned around, and landed uneventfully with its 147 passengers at Minneapolis.

The NTSB faulted the pilots for allowing themselves to become distracted to the point of incommunicado, but it found plenty to comment on regarding the air traffic control situation that abetted the out-of-hand situation:

“The NTSB also found that air traffic controllers did not follow procedures to ensure NWA 188 was on the correct frequency, which delayed the identification of NWA 188 as NORDO, and that no national standardized procedures exist when automated information transfers are used instead of the paper flight-progress strips to nonverbally document and confirm ATC information among controllers.”

In other words, the newer high technology system that replaces paper strips may be more vulnerable to a runaway NORDO. The Denver and Minneapolis ATC facilities, like many nationwide, now use automated systems to track and hand off flights between controllers. FAA Order 7110.65, “Air Traffic Control,” does not require any control coordination or instructions.

The NTSB noted:

“In the case of NWA 188, controllers did not document, and under FAA directives were not required to document, control information that the flight crew had been directed to contact subsequent sectors or that the flight crew had not yet made that contact ….”

“While NWA 188 was NORDO, ATC controllers would not have been able to quickly communicate with the flight crew in the event of a conflict with another aircraft or the occurrence of some other emergency. Thus, the NTSB is concerned that the lack of national standard procedures for documenting and sharing information about radio contact with flights may result in flights that are out of contact for longer periods (because their NORDO status is not detected), thereby degrading safety of flight.”

In December 2009 the NTSB asked the Federal Aviation Administration (FAA) to provide any ATC corrective action as a result of the NWA 188 incident. The FAA replied that it asked En Route and Oceanic Services to issue a memorandum requiring en route facilities to develop an acceptable procedural and visual cue to indicate the communication status of each aircraft.

The NTSB was not impressed:

“Although the implementation of these FAA actions will improve the documentation of aircraft communication status, the actions only apply to en route facilities [those that manage traffic at the highest levels over the U.S. and far out into the Atlantic and Pacific oceans], not all ATC facilities. Further, these actions do not address other types of control information that should be documented, such as the issuance of an instruction that would typically require the controller to confirm that the instruction has been completed.”

NTSB investigators also noted that the controller at Minneapolis tried, in frustration, to contact NWA 188 on the universal emergency frequency, 121.5 MHz. The controller was not required and did not announce during transmission that this was an emergency situation.

NWA 188 had one of its radios tuned to 121.5 MHz, but the pilots either had the volume turned down or were distracted by their conversation.

The NTSB notes that when an airplane has an emergency, a radio transmission on this frequency is preceded by the word “Mayday.” There is no comparable phrase for emergency transmissions from the ground to the air. The NTSB believes a phrase such as “on guard” would contribute to the “saliency” of the message:

“Such identification highlights the importance of the transmission and increases the likelihood that flight crews and air traffic controllers monitoring multiple frequencies would give attention to emergency transmissions.”

As a result of its findings, the NTSB had no recommendations for the airlines. But it did recommend that all air traffic controllers have a system for monitoring changes from one sector to another (to prevent NORDO from dropping into a black hole). It also recommended standard phraseology, such as “on guard,” to identify transmissions over emergency frequencies as emergencies.

A very basic question arises. Why does it take an NTSB investigation to raise such obvious issues? Surely, someone in the air traffic control system thought of these improvements. If not, why not? If they were raised, why weren’t they adopted?

The obtuse FAA answer that En Route controllers (but not terminal controllers) should track the communications status of each aircraft does not give confidence.

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