A communication system designed to put air-traffic controllers in instant contact with the military in the event of a security threat had so many problems that it was "unusable," a report on the jet that flew past its destination revealed Dec. 16.

Hundreds of pages of documents released by the National Transportation Safety Board (NTSB) add new details to a string of errors, technical glitches and miscommunications that hindered efforts to reach Northwest Airlines Flight 188 in October and to alert the military about the suspicious jet. They also shed light on the frantic moments when the pilots first realized they had flown past their destination.

Due to apparent mix-ups, controllers never tried to radio the pilots on the last radio frequency they had spoken on, according to the preliminary NTSB report. At least initially, the controllers also did not attempt to reach the pilots on a radio frequency reserved for emergencies, the NTSB said.

Investigators also had difficulty reconstructing some of the event because telephones are not recorded at an air-traffic facility near Minneapolis, despite repeated requests by the facility to install recording equipment, according to the reports.

Northwest Airlines Flight 188, which was out of contact with controllers for one hour and 17 minutes, landed safely on Oct. 21 after flying about 150 miles past its destination in Minneapolis.

The pilots told investigators that they became distracted while working on their private laptops, a violation of airline rules. They insisted they had not fallen asleep and said they had no idea anything was amiss until one of the flight attendants tried to reach them on an intercom system, prompting a confusing rush to regain radio contact.

Flight attendant Barbara Logan told investigators she had called the pilots to ask when they would be landing. The pilot who answered told her he was "hosed" and hung up.

Capt. Timothy Cheney of Gig Harbor, Wash., told investigators that he looked up at the computer screens that display flight information on the Airbus A320 and saw that they were essentially blank because the jet had already flown its assigned route. After adjusting another display, he saw that Eau Claire, Wis., was ahead.

The startled captain later told investigators he was "in shock" as he instructed co-pilot Richard Cole of Salem, Ore., to contact controllers because "we need to get this thing on the ground."

"I've never, ever, been in this situation," he told investigators. He said he had put "passengers at risk."

"You don't know how sorry I am," he said.

Cheney and Cole were stripped of their pilot licenses by the Federal Aviation Administration (FAA). Both men have appealed the revocations, blaming controllers in part for the problems. Federal aviation law requires that pilots maintain contact with controllers.

The FAA last month, acknowledging that controllers had originally failed to raise an alarm about the jet, said that controllers should have notified the military within five to 10 minutes after realizing that the jet was out of contact. Instead, the Domestic Events Network (DEN), which coordinates aviation security concerns between civilian and military agencies, was not notified until minutes before the pilots resumed contact.

Part of the problem appears to have been the communication system between the FAA's Minneapolis Center and the DEN. The special phone line is located in a spot where the facility's manager never goes while handling an emergency.

FAA air-traffic managers said that the communication equipment "does not operate adequately in a consistent manner." Its volume rises and falls uncontrollably, and it suffers from loud feedback and clicking noises that render it "unusable."

The supervisor in Minneapolis said she did not notify the DEN earlier because she did not realize that it had not been contacted.

More than 30 minutes passed from the time that Flight 188 last spoke with a controller and another controller began raising concerns, according to NTSB and FAA documents. Because of the lengthy time, controllers had a difficult time piecing together what radio frequency the pilots had last used.

Pilots change radio frequencies dozens of times during a flight as they are handed off from one controller to another.

As a result, it appears likely that the pilots on Flight 188 may never have heard controllers frantically radioing them as they cruised overhead at 37,000 feet.

After flying into Wisconsin, one of the pilots attempted to radio controllers using the wrong frequency. He reached a controller across the border in Canada.

Once the controller realized the Northwest jet's location, he instructed the pilots to contact the correct frequency.

Alan Levin is a reporter for USA Today.