Lingering mystery why pilots flew 150 miles past destination

A co-pilot who “forgot” to land says he was not asleep and there was never any danger to passengers but why pilots flew 150 miles past their scheduled airport remains a mystery as investigators struggle for answers.
 

The first officer of Northwest Flight 188 also denied a strong disagreement with the captain may have caused the problem, as earlier reports suspected.
 

"We were not asleep; we were not having an argument; we were not having a fight," said pilot Richard Cole.
 

Flight 188, which was carrying 144 passengers and five crew members from San Diego to Minneapolis, lost touch with controllers east of Denver. It then traversed the Plains, flew across busy airways carrying flights to Chicago and crossed into Wisconsin before turning back to Minneapolis.
 

Pilots have given various evasions and explanations but in one recent story, they said they were distracted by their discussions of a new monthly flight-schedule system.
 

The pilots admitted they used their personal laptop computers during the discussion, which violates company policy, according to the National Transportation Safety Board.
 

The flight by Delta’s Northwest unit was coming from San Diego. The Northwest Airbus A320 flew over Wisconsin about 150 miles (241 kilometers) past the Minneapolis airport before turning around and heading back to its destination, according to Houston-based flight-tracking service FlightAware.com.
 

Air-traffic controllers and pilots tried for more than an hour to contact Cole and co-pilot Timothy Cheney using radio, mobile phone and data messages.
 

"It was not a serious event, from a safety (perspective)," Cole told the AP. "I would tell you more, but I’ve already told you way too much."
 

So what caused the problem?
 

The cockpit voice recorder may not tell the tale.
 

New recorders retain as much as two hours of cockpit conversation and other noise, but the older model aboard Flight 188 includes just the last 30 minutes – only the very end of the flight after the pilots realized their error over Wisconsin and were heading back to Minneapolis.
 

Wthout data from the plane’s cockpit-voice or flight-data recorders, it may be hard for investigators to conclusively back up pilot assertions or precisely determine what happened.
 

Cole would not discuss why it took so long for the pilots to respond to radio calls, "but I can tell you that airplanes lose contact with the ground people all the time. It happens,” he said.
 

Cheney and Cole have been suspended. They risk license suspension and a possible civil penalty.
 

A police report said the pilots passed breathalyser tests and were apologetic after the flight.

Fatigue was not an apparent issue since they had just started their work week and were coming off a 19-hour layover.
 

Aviation safety experts said it was more likely that the pilots simply fell asleep.
 

Pilots typically engage autopilots after take-off, rely on flight-management computers to navigate and adjust speeds while cruising, then program descent trajectories to approach runways. During a trip of more than three hours, pilots essentially monitor instruments in a darkened cockpit. Research has demonstrated that under those conditions, pilots can doze off without realizing it.
 

Research has shown that short naps mid-flight could help make pilots more alert during landings. While strictly forbidden in the US, such "controlled napping" is endorsed under certain conditions by some foreign carriers.
 

The investigation also is bound to revive the longstanding controversy over installing cockpit video recorders — something the safety board advocates and pilot groups continue to strenuously oppose.
 

By David Wilkening