Off course, out of touch: What were Northwest Airlines Flight 188 pilots doing?

Safety investigators are skilled at solving the mystery of plane crashes. But with Northwest Airlines Flight 188, which landed safely, they are tackling a different puzzle: What went on in the cockpit to cause the jetliner to fly for 88 minutes without radio contact and well beyond its destination?

Investigators sought Friday to explain why the pilots of the San Diego-to-Minneapolis flight did not begin a normal descent when they should have Wednesday night.

Capt. Timothy Cheney, 53, of Gig Harbor, and First Officer Richard Cole, 54, of Salem, Ore., told investigators they were having a heated discussion about airline policy and lost track of where they were.

Skepticism of that explanation resounded throughout airline and aviation-safety circles, and speculation centered on whether the pair had fallen asleep.

"I can assure you none of us was asleep," Cole told ABC News on Friday night. He declined to comment further but added, "I am not doing very good."

Cole elaborated in an interview Friday night with The Associated Press: "All I'm saying is we were not asleep; we were not having a fight; there was nothing serious going on in the cockpit that would threaten the people in the back at all."

He declined to discuss what exactly happened but did insist "it was not a serious event, from a safety issue."

"I can't go into it, but it was innocuous."

On to Wisconsin

Two aviation officials from separate agencies said Wednesday's flight was the first of the day for both pilots, who were coming off a layover of approximately 17 hours.

Instead of landing the Airbus A320, with 144 passengers and three flight attendants aboard, the pilots flew past Minneapolis to the skies above Eau Claire, Wis., despite repeated radio and cellphone calls from controllers and other pilots and e-mails from the airline's dispatchers.

When the plane was 110 miles past the airport, the pilots finally responded, after being alerted by a flight attendant who called on an intercom from the cabin, according to a report from Minneapolis-St. Paul airport police. The plane turned around and landed safely.

Two pilots flying in the vicinity were also finally able to raise the pilots using a Denver traffic-control radio frequency instead of the local Minneapolis frequency.

With worries about terrorists high, even after contact was re-established, air traffic controllers asked the crew to prove who they were by executing turns.

The pilots were suspended by Delta Air Lines, which merged with Northwest last year and operates its flights, pending the outcome of investigations.

Both passed breath-analysis tests to check for alcohol, according to the police report. When the plane landed, the report said, Cheney turned to waiting officers and gave a "two-thumbs-up" sign through the cockpit window.

Officials at the National Transportation Safety Board (NTSB) planned to listen to the plane's cockpit voice recorder, but it might not provide many answers. The recorder, which runs continuously throughout a flight, is an older model that has only 30 minutes of sound and records over itself. The officials said they would interview the pilots this weekend.

88 minutes of silence

Federal aviation officials said the radio communication with the plane ceased after 6:46 p.m., Central Time, and did not resume until 8:14 p.m., a gap of 88 minutes — a long time for a commercial jet over the continental United States that has not had a system failure or whose radio is not tuned to the wrong frequency.

Pilots normally wear headsets with microphones or transfer air traffic controllers' audio to a loudspeaker. Unless the radio was tuned to the incorrect frequency, "if you're awake, you're going to hear," said the former chief executive of a major airline, who spoke on condition of anonymity.

More than a dozen controllers, including those at three centers tracking the flight — one in Denver and two serving the Minneapolis airport — tried to contact the pilots, said Doug Church, a spokesman for the National Air Traffic Controllers Association.

"It was all hands on deck," Church said.

At least one of the Minneapolis-focused flight-control rooms made 13 attempts, an official said.

The plane was cruising at 37,000 feet when the crew stopped responding to air traffic controllers and airline dispatchers about 400 miles west of Minneapolis, and an hour and five minutes before its scheduled arrival of 8:01 p.m.

When the plane should have been descending, it was flying at a constant altitude, according to FlightAware, a company that provides real-time tracking of airplanes based on Federal Aviation Administration (FAA) radar data. It showed that the plane flew northeast at a constant altitude from 7:13 to 7:53 p.m., making one 19-degree turn in that period.

Daniel Baker, the company's chief executive, said the plane could easily have made that turn, and maintained its altitude and speed, with instructions that were programmed into the autopilot, and "without active human involvement."

Fighter jets readied

Once the repeated attempts to reach the plane were unsuccessful, federal agencies ramped up their efforts. The North American Aerospace Defense Command readied four fighter jets.

Meanwhile, the Transportation Security Administration (TSA) took part in conference calls with other federal agencies and checked for "possible screening anomalies" at the San Diego airport, said Sterling Payne, a TSA spokeswoman.

The plane, meanwhile, flew so smoothly above the thick layer of clouds that Brent Bjorlin, a passenger, said he never suspected a problem until the landing, when police officers boarded the plane.

"When they opened the doors, that's when we thought something was wrong; they told us to take our seats," said Bjorlin, 44, of St. Michael, Minn.

Some passengers said they were aware the plane was off course. "We weren't circling around the city, and that's why it wasn't adding up in my mind," said Anne Kroshus, a real-estate broker from Woodbury, Minn. "Why are we still way up in the air and nobody's saying anything?"

"A very responsible guy"

Cole's former wife, Barb Buttler, said Friday, "He was a very serious pilot. He was a very even-tempered person."

In Gig Harbor, Dorothy Wilson, a next-door neighbor to Cheney and his family for more than 10 years, said Friday that he is a "super guy."

"He's a very responsible guy, so this just floors me," she said. "I would sing his praises above almost anyone. He is the best neighbor we have ever had."

Wilson said she and her husband are in their 80s. Because of that, Cheney checks on them and invites them for boat rides, movies and other entertainment with his family. She said his yard is a "showplace" and he does all the work himself.

Cheney has a wife, Sandra, and two grown children, Wilson said. Son Joel Cheney is in the military, Wilson said.

"I am just stunned about what happened," she said. "We are very supportive of him and his family."

Another neighbor, Robert Crist, described Cheney as a "fastidious" person whom he presumed to be a distinguished pilot. "He strikes me as a guy who is disciplined," Crist said Friday, describing himself as a frequent customer of Northwest Airlines.

"I can see why people want to know" what happened, Crist said, adding that he would have no problem with Cheney piloting a plane on which he was flying.

After reading media accounts of the flight, Bjorlin, the passenger, said he was flooded with concerns about the pilots' inattention. "What if the fuel gauge was empty?" he said. "What else might have happened?"

Seattle Times staff reporter Steve Miletich contributed to this report. Material from the Minneapolis Star Tribune and The Associated Press is included in this report.