Two pilots of a Northwest Airlines flight Wednesday were apparently so distracted that they missed their airport and kept flying for 150 miles before landing the plane and its 147 passengers safely.
For one hour and 18 minutes, the pilots -- flying at 37,000 feet above sea level -- were radio silent as air traffic controllers at times tried to reach the cockpit, according to a news release from the National Transportation Safety Board.
As the event unfolded, concern was high among air traffic controllers, who repeatedly attempted to establish contact during the incident, using multiple methods, the air traffic controllers union told ABC News. Eventually, controllers asked other planes in the air to attempt to contact the Northwest plane, a method that the union said ultimately proved successful.
The pilots of the Airbus A320 told the FBI and airport police that they were in a heated discussion over airline policy and they lost awareness of the situation, the Federal Aviation Administration said.
The NTSB plans to interview the crew and is reviewing the cockpit voice recorder and flight data recorder of the flight, Northwest 188 from San Diego to Minneapolis. The NTSB will be investigating whether the pilots fell asleep, along with all other possibilities.
"There wasn't any problem on board -- nothing," Andrea Allmon of San Diego told ABC affiliate KSTP. "We landed, everyone got ready to get off the plane and suddenly police were getting on the plane and telling us to sit down. They went into the cockpit, looked around and then told everyone to get off the plane."
Early in 2008, the two pilots of a go! Airlines flight from Honolulu to Hilo, Hawaii fell asleep for at least 18 minutes while in the air. The plane flew past the airport and out to sea before air traffic controllers finally were able to reach the pilots, who turned the plane around. The captain later was diagnosed with sleep apnea.
Delta Airlines, which now owns Northwest, said in a statement that 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," Delta said in the statement. "The pilots have been relieved from active flying pending the completion of these investigations."
Asked how many years of service the pilots have and how many hours they were into their shift, a Delta spokesman said, "We are not sharing as that is all part of the investigation."
This is the second instance in just days of a Delta flight crew having an apparent safety lapse. Monday at 6:05 a.m., Delta flight 60 from Rio de Janeiro to Atlanta landed on a taxiway instead of the parallel runway where it was supposed to touch down. There were no injuries to any of the 182 passengers or 11 crew members on the flight.
ABC News' Matt Hosford and Lisa Stark contributed to this report.