Pilots Apparently Tuned To An Incorrect Frequency

The NTSB has released about 400 pages of documents representing the investigation into Northwest Flight 188, which overshot its destination of Minneapolis by about 150 miles. The pilot told the NTSB they were out of communication with ATC because they had tuned to the wrong frequency when the handoff came from Denver, and then became distracted by a discussion of company route bid policy.

The report summary states that "Both pilots stated in interviews that during the flight, they both heard “chatter” on the radio frequencies, but did not recall hearing their call sign, and that the amount of ATC radio calls was “no more than usual”."

"(T)he captain said he began a conversation regarding the current Preferential Bidding System (PBS). The Delta PBS system being used by the Northwest crews had been recently implemented as part of the integration of Northwest Airlines and Delta Air Lines. While computer tutorials, crew services volunteers and a 150 page manual had been provided to the Northwest crews to learn the new PBS system, both pilots characterized the system as confusing. The captain had recently received his November bid results and downloaded the results on his laptop computer. He commented to the F/O that he did not receive the bid results he had anticipated, and it would require him to commute to MSP more often. The captain then pulled out his laptop computer to show the F/O his bid results. According to the captain, he placed his laptop on his lap, although the F/O stated the captain had placed his laptop out on the extendable tray table. The captain stated that with his laptop out, his view of the Primary Flight Display (PFD) was not blocked. After 4-5 minutes of conversation, the F/O pulled out his laptop computer and placed it on top of the extendable tray table in front of him. The captain stated that he then placed his laptop to his left and on top of his flight bag and it remained there until he retrieved the arrival charts for MSP, but he also later stated that both laptops were out at the same time. The F/O stated that both laptops were out and opened at the same time, and that the captain’s laptop was on his tray table. Both pilots acknowledged there was a continued discussion on the PBS system, with the F/O tutoring the captain in regards to the bidding system and process because of his familiarity and comfort with the bidding system."

Both pilots told the NTSB they were not sleeping and not arguing. Again, quoting the report "The pilots stated that their first indication of anything unusual with the flight occurred when they received a call from a F/A inquiring about their arrival. The captain said he looked down at his Multifunctional Control and Display Unit (MCDU) and saw there was no flight plan information depicted. They said they did not see the lights of Minneapolis due to the overcast sky conditions below. The captain then turned his NAV display from ARC mode to ROSE (compass) and saw Duluth, MN to his left and Eau Claire, WI at “the 2 o’clock” position with no estimated time of arrival (ETA) information shown for their destination. The F/O said he “immediately” contacted ATC, but neither pilot could remember what frequency they used, and said “someone” gave them a frequency to contact MSP Center. It was determined that the crew inadvertently contacted Winnipeg Center, which gave them a frequency to established contact with MSP Center. The F/O then noticed the ACARS message indication on the ECAM, and attempted to retrieve those messages. He stated that he noticed several “contact ATC” messages from dispatch, but “inadvertently” pushed the “delete all” button erasing all the dispatch messages."

The plane went on to land normally, about 30 minutes behind schedule. "After a brief conversation with officials, the crew was administered a field breathalyzer test. Neither pilot could remember what happened to the cockpit paperwork, but both stated they believed the Northwest Chief Pilot who met the aircraft may have taken possession of it."

An examination of the Cockpit Voice Recorder showed that the ambient cockpit microphone had malfunctioned, and meaning that while all communications with ATC and the aircraft PA system recorded normally, there was no recording of the conversation that went on in the cockpit. Much of the conversation would have been overwritten anyway, as the type of recorder installed in the aircraft records over the oldest audio data in a loop-type fashion. When the CVR is deactivated or removed from the airplane, it retains only the most recent 30 minutes of audio.

CVR Microphone NTSB Photo

As a result of the incident, both pilots' certificates were revoked by the FAA, and they were suspended by Northwest Airlines.

FMI: www.ntsb.gov