A small cargo plane was improperly taxiing on an active runway for more than a minute at Denver International Airport a week ago before air traffic controllers were warned of a potential collision with an arriving Frontier Airlines jet, safety investigators said Thursday.
The pilot of the Key Lime Air turboprop was directed by controllers to taxi from DIA's cargo area to the airport's west side for takeoff, according to the National Transportation Safety Board.
The small plane's pilot said blowing snow reduced his visibility and "as he attempted to find the centerline lighting" on the taxiway, "he saw blue taxi lights, followed them and turned onto runway 35L," the NTSB said in a preliminary report.
The Key Lime plane entered that runway only seconds after another commercial jet had landed on it, according to officials familiar with the investigation.
"We take full responsibility for what happened," said Todd Schleibaum, chief pilot at Key Lime Air, "but there were an awful lot of mitigating circumstances," including weather, which might have obscured signs.
The incident occurred at 7:28 a.m. in light snow and mist with half-mile visibility.
"The airport has numerous visual cues at every runway entrance, mandated by the Federal Aviation Administration, to ensure the highest degree of safety," DIA spokesman Steve Snyder said Thursday. "We know for a fact that the large runway signs and runway guard lights for the area in question were visible during the storm."
As the Key Lime pilot was trying to find the proper north-south taxiway, he passed another taxiway that was being used as a temporary snow dump.
The NTSB report indicates that controllers lost track of the taxiing Key Lime plane for a time, but Snyder said the snow pile met federal aviation regulations and should not have impeded ground radar signals that allow controllers to monitor the planes on the airfield.
A controller in DIA's tower asked the Key Lime pilot to identify his location about a minute after the small plane entered the runway, the report said. At that moment, the pilot "noticed that he was on a runway."
Seven seconds later, alerts in the tower warned controllers that the Frontier plane was within seconds of landing on an occupied runway. The tower controller alerted the Frontier crew to abort the landing.
In a separate bulletin that highlights NTSB's "Most Wanted" safety improvements, the agency said the current warning system "is not adequate to prevent serious runway collisions because too much time is lost routing valuable information through air traffic control."
It added: "Alerts may occur as little as 8 to 11 seconds before a potential collision."
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