Airplane Overflies Its Destination: Will The Tapes Tell the Tale?

It's an understatement to say federal investigators are baffled by an incident last Wednesday in which Northwest Airlines Flight 188, from San Diego to Minneapolis-St. Paul, overshot its destination by roughly 150 miles. The incident, which ended safely when the plane turned around and landed at its intended destination, is under investigation by the National Transportation Safety Board. Privately, sources close to the investigation, who asked for anonymity when discussing an open inquiry, say that explanations available so far for what happened do not make much sense.

According to a statement issued by the NTSB, the highly automated Airbus 320 was cruising at 37,000 feet when, at 5:56 pm Mountain time, air-traffic controllers lost voice contact with the plane. According to the NTSB, controllers did not reestablish contact with Flight 188's crew until 8:14 pm Central time—meaning the flight was out of touch with air-traffic control for one hour and 18 minutes. Throughout the period during which the crew was out of contact, an official said, the plane was being fully tracked by radar and air-traffic controllers were trying repeatedly, but unsuccessfully, to reach the crew. An official of the air-traffic controllers' union told The Wall Street Journal that by the time the aircraft, still incommunicado, had overflown Minneapolis-St. Paul airport, ground control had become concerned about the possibility of terrorism. The Federal Aviation Administration contacted military authorities and fighter planes were readied for possible attempts to intercept the wayward flight.

According to the NTSB, when controllers finally did reestablish contact with the flight crew as the plane was somewhere over Wisconsin, the controller reported that the crew had become distracted and asked to return to their scheduled destination. Controllers did direct the plane in a series of maneuvers back to Minneapolis-St. Paul. According to the NTSB, the FAA, which licenses pilots and runs the air-traffic-control system, said that the crew told the FBI and airport police upon landing that they had been in a "heated discussion over airline policy and they lost situational awareness." The NTSB said it was scheduling its own interview with the crew, and had also ordered that the plane's "black box" flight recorders be sent to the NTSB's laboratory in Washington for examination; the devices are expected to arrive there by Friday afternoon.

Officials close to the case say that at best they find the crew's initial explanation for why they were out of touch—because they were engaged in an argument—puzzling, if not unbelievable, since it's hard to imagine such an argument being so intense and so lengthy that they would ignore increasingly frantic calls from controllers for more than an hour. Also hard to credit is one of the principal alternative explanations that have surfaced in the media—that the pilots dozed off—since it stretches credulity that two experienced pilots would both fall asleep at the controls for more than an hour while controllers were squawking frantic appeals into their headsets. On the other hand, the FAA and NTSB have periodically expressed concern that the stressful schedules that commercial pilots must follow can cause dangerous levels of fatigue that can lead to serious or fatal accidents.

Flight 188's black boxes may contain evidence to resolve the mystery conclusively, but they may not. One key issue will be the recording capacity of the cockpit voice recorder, which records sound through several cockpit microphones. Some voice-recorder models can only record 30 minutes worth of data; if that is the case with the recorder on Flight 188, then it is possible the recorder will not tell the full story of what the pilots were up to during the 78 minutes they were out of touch with the ground. One theory already being discussed among experts is that perhaps the pilots fell asleep, and, upon awakening, and knowing that the voice recorder only had a 30 minute capacity, decided to fly around for a while so that the recorder would erase evidence of what went on. But more modern recorders can record up to two hours of sound, and if Flight 188 had such a recorder—which is not yet known—then this theory probably is invalid.

The Associated Press reported that airline had suspended the two pilots of Flight 188, who have not been identified. In a written statement, Delta Airlines, which owns Northwest, said: "The safety of our passengers and crew is our top priority. We are cooperating with the FAA and NTSB in their investigation as well as conducting our own internal investigation. The pilots have been relieved from active flying pending the completion of these investigations."

Update: Investigators have now said the cockpit voice recorder on the flight was the older version, which records for 30 minutes at a time, rather than 150 minutes.