Two Northwest Airlines pilots flying from San Diego to Minneapolis on Wednesday night failed to respond to radio calls for more than an hour and overshot their destination by 150 miles. They didn’t realize what had happened until the flight attendants got their attention through the intercom somewhere over Wisconsin. The flight’s first officer says that he and the captain did not fall asleep at the controls, as some had speculated. Government investigators said on Monday that the pilots were using their laptops to check crew scheduling and lost track of time. If the pilots were napping or distracted, couldn’t air traffic control have gotten through by yelling into their headsets?
Not if the volume was turned down or if the flight crew was listening to a different radio. Most commercial pilots wear their headsets for the duration of a flight, although they can switch over to a cockpit speaker. Either way, there’s always a radio on in the cockpit. That doesn’t mean the crew is always listening for voice communications from the ground, however. Pilots can alternate between two different radios: one for talking to air-traffic controllers and another for receiving navigational information in Morse code from ground-based radio beacon s. (You can’t listen to both radios at the same time.) These days, most planes have more sophisticated positioning systems that make listening to dots and dashes optional, but many pilots still switch over to navigational radio from time to time. Under normal circumstances, the co-pilot would remain on the voice channel while the captain switched.
A pilot would never get confused about which radio he was hearing, so long as the volume was turned up. It is possible to adjust the headset or cockpit speaker levels with a knob on the console such that they’re nearly silent. But there isn’t much reason for a pilot to silence his communications radio during a flight.
A cruising jet usually makes contact with the ground every 10 minutes or so as it is handed off from one controller to the next. When the plane is about to leave a given controller’s jurisdiction, that controller instructs the pilot to change radio frequencies. The pilot confirms receipt of the information by repeating it back, then makes the switch and contacts the new controller. (Based on the location and speed of the Northwest flight, the pilots should have communicated with the ground at least five times in the course of an hour—and probably more, since they were approaching their destination.) When conditions are good, these are often the only communications between the plane and the ground in mid-flight. Even during the intervals between handoffs, the pilot should hear communications between air traffic control and other flights.
If controllers on the ground get no response during a handoff, they’ll send text messages to a data unit on the aircraft’s console in addition to their repeated radio calls. If they think there is a problem with reception, they might ask other pilots in the vicinity to radio the taciturn aviator. If the plane’s radio has stopped working entirely, the pilot is supposed to let controllers know by sending them a message through the aircraft’s transponder. In any event, air traffic controllers do not yell into the radio. Keeping your cool during an emergency is an important part of aviation culture.
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Explainer thanks Chris Dancy of the Aircraft Owners and Pilots Association, Steve Jones of Western Michigan University, and Paul Takemoto of the FAA.