Controllers Disagreed on Fog, Probe Told

In the moments before two Northwest Airlines jetliners collided on a runway in heavy fog last December, air traffic controllers disagreed on whether visibility was adequate, but none of them said anything about it to the Northwest pilots, testimony and documents showed Thursday.

Controller Marianne Frances Becker said she checked the visibility before starting her shift and concluded it was no more than one-eighth of a mile--far less than the one-quarter mile required for takeoff on the runway where the crash occurred.

But she said that, when she asked Armando Gonzalez--the controller handling takeoffs on that runway--if he wanted to change his estimate of one-quarter of a mile, Gonzalez said his estimate was accurate.

Seconds later, a DC-9 strayed onto a fog-shrouded runway and was struck by a Boeing 727 that was taking off at more than 100 miles an hour.

The pilots of both planes have testified that they were unable to see each other until it was too late to avoid the collision.

The testimony and documents reviewed Thursday were presented at a National Transportation Safety Board hearing to determine the cause of the accident that killed eight and injured 21.

Although attention has focused on the DC-9 cockpit crew’s inability to find its way around the airport in the worsening fog, there has also been testimony that pilots often find the airport’s complex layout and directional signs confusing and that controllers may not have kept pilots properly advised before the accident.

Because of the fog, none of the controllers could see the planes they were directing, and they had to rely instead on position reports radioed by the cockpit crews.

Gonzalez, who was responsible for determining visibility at the time of the crash, told NTSB investigators that he used his experience in viewing familiar airport landmarks to conclude that the visibility was adequate.

Moments before the crash, Gonzalez said, he heard another controller, who was handling the DC-9, say that the plane apparently was lost in the fog and might have strayed onto the runway.

But, by that time, Gonzalez said, he had already cleared the Boeing 727 to take off, and he assumed it was already airborne.

He said his decision not to tell the 727 to abort the takeoff immediately was based on that assumption.

However, subsequent investigation has shown that the 727 was still on the runway, and approximately seven more seconds would elapse before it struck the DC-9.

Whether the 727 could have avoided the collision if an immediate abort warning had been issued is a matter of conjecture, but sources close to the investigation say the plane probably could have slowed enough to reduce the damage and injury on impact.

Representatives of the National Air Traffic Controllers Assn., which has been excluded from participation in the investigation, have complained that the NTSB “isn’t getting the controllers’ perspective.”

Jim Burnett, the NTSB member heading up the investigation, said that the controllers’ association was excluded at the request of the Airline Pilots Assn. after the association leaked then-confidential NTSB information to the news media.