Northwest Flight 188: A Heated Discussion or Pilot Fatigue?
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Everyone has heard about the Northwest Airlines flight that departed San Diego bound for Minneapolis-St. Paul (MSP), and flew 150 miles past its destination before turning back and landing. According to the NTSB, after landing the pilots told the FBI and airport police that they had been in a heated discussion over airline policy and lost situational awareness. The FAA tracking data on the flight shows that the aircraft began its decent for landing more than 48 minutes before it eventually touched down at MSP. The cockpit voice recorder (CVR) is being analyzed by the NTSB, but it will only reveal the last 30 minutes of cockpit conversation before the aircraft was powered down at the arrival gate. So unless the pilots actually discussed what had happened during the last 30 minutes of the flight, it is unlikely the CVR will provide any clues. The flight data recorder (FDR), which records aircraft systems data and pilot flight control inputs, is also being analyzed by the NTSB. Pursuant to normal operating procedure, the autopilot would have been flying the aircraft while the pilots monitored the aircraft systems and communicated with air traffic controllers (ATC). Since the autopilot flies the aircraft with precision, and since the systems on an A320 are highly automated, as long as all the aircraft systems are operating normally there is nothing for the pilots to do in cruise flight. It is therefore unlikely the FDR will provide any clues as to what may have happened.
The flight departed San Diego at 3:00 PM PDT, and the NTSB says that ATC "lost radio communications" with the flight at 5:56 PM MDT. What the NTSB means by "lost radio communications" is not clear. Does the NTSB mean that the last ATC communication with the flight took place at 5:56 PM MDT, 1 hour and 56 minutes into the flight, or does the NTSB mean that at 5:56 PM MDT ATC unsuccessfully tried to communicate with the flight? FAA flight tracking data shows that at 5:17 PM MDT the flight began a climb from its initial cruise altitude of 35,000 feet to its final cruise altitude of 37,000 feet. If the last successful ATC communication with the flight was the instruction to climb to 37,000 feet, and 39 minutes later at 5:56 PM MDT ATC unsuccessfully tried to reach the flight, is it possible that a heated discussion about airline policy would prevent both the Captain and First Officer from responding to ATC radio calls? According to the NTSB, controllers "reestablished communications" at 8:14 PM CDT. This means that, according to the Captain, he and the First Officer were in a heated discussion for something between 1 hour 18 minutes and 1 hour 57 minutes, and it was so heated that they lost track of where they were. FAA flight tracking data shows a groundspeed of about 600 knots when MSP was overflown, and according to the NTSB the flight went another 150 miles, which would have taken about 15 minutes. This means the discussion was so heated that neither pilot realized they had arrived at their destination until about 15 minutes after they passed it, and and it was so heated they could not hear the frantic ATC calls that most certainly occurred. Or is it more likely that with nothing to do but monitor systems, and with no ATC communication for 39 minutes, the pilots were fatigued and fell asleep? Without knowing details of their working hours, it is impossible to say at this time whether fatigue played a roll. But pilot fatigue has resulted in known past incidents where crews fell asleep, and crew fatigue should not be ruled out here.
