When a small plane entered a Denver International Airport runway as a Frontier Airlines jet was about to land last January, “it looked like the aircraft were going to hit,” according to an air traffic control manager monitoring radar in DIA’s tower.
To avoid a collision, one controller screamed to another to get the Frontier plane to pull up and go around.
On Wednesday, the National Transportation Safety Board released a detailed report on the Jan. 5 incident — one of 24 serious runway incursions at U.S. airports in the year that ended Sept. 30.
The NTSB’s account describes how the pilot of the Key Lime Air turboprop missed a planned turn onto taxiway M and instead turned left onto runway 35 Left at the next intersection.
It also recounts how two tower controllers handling traffic on DIA’s east airfield were uncertain of the whereabouts of the Key Lime plane as they scanned various radar and surface-detection screens in the tower.
Because of blowing snow, visibility was low and controllers were relying on the tower instruments.
As Frontier Flight 297 continued its final approach to 35 Left, the Key Lime pilot taxied north on the runway for one minute and 10 seconds before a safety system in the tower issued verbal and visual alerts, according to the NTSB’s report.
In the seconds before the alerts, a controller watching the Airport Movement Area Safety System (AMASS) surface-detection display in the tower sensed “something wasn’t sitting right” about the location of the Key Lime plane, according to the report.
As he pointed to the display, “the AMASS alert went off and he screamed to the local controller to send the Frontier around,” NTSB said.
“The aircraft missed colliding by approximately 50 feet,” the safety agency said.
DIA detection systems
In an interview with the NTSB, the tower manager who also was monitoring consoles at the time of the incursion said “it was unreasonable that the (Key Lime) aircraft was on the runway for approximately 60 seconds prior to the event and that he expected the ground controller to see it ‘pretty quickly,’ ” the report said.
NTSB said it asked the ground controller “if he had any discomfort” with the Key Lime plane being on the runway for about a minute and “he stated that he did and that he would have ‘loved to have caught it earlier.’ ”
DIA’s tower relies on two key technologies for collision avoidance — AMASS and an older radar system called ASDE-3.
ASDE stands for Airport Surface Detection Equipment, and at some U.S. airports the Federal Aviation Administration has installed an upgraded model, ASDE-X, that integrates data from radar and aircraft transponders to give controllers more precise information on the location of planes and airfield vehicles.
DIA is on the list to get ASDE-X, but it is not expected to be in operation in Denver until 2009, according to FAA officials.
Piled snow in sightline
Last month, DIA controllers told a visiting FAA runway safety team that the requirement for controllers “to share ASDE displays was a contributory factor” to the January incident, according to the team’s report.
Providing more displays would help controllers “detect problems more quickly,” said the runway safety team’s report.
On Wednesday, FAA spokesman Allen Kenitzer said the agency is “actively working” to get more ASDE-3 displays for DIA’s tower.
NTSB chairman Mark Rosenker has said even ASDE-X doesn’t solve the incursion problem because it still requires controllers to transmit verbal alerts of an impending collision to pilots.
The NTSB wants the aviation industry to develop a technology that will warn pilots directly without the alert first going to controllers.
The NTSB’s report on the Jan. 5 incident also faulted DIA for piling so much snow on a cargo-area taxiway in the weeks before that it blocked radar returns from the airport’s existing ASDE system.
After the incursion, DIA managers instructed employees to pile snow in areas that do not interfere with “line of sight” from the airport’s two ASDE antennas, the NTSB said.
FAA listed the Jan. 5 incident as one of the year’s most serious Category A incursions, defined as those in which “participants take extreme action to narrowly avoid collision.”
DIA was the only U.S. airport with two Category A incursions. The other occurred Feb. 2 when an airport snowplow operator drove across a runway in front of a United Airlines jet that had just landed.
United pilots used emergency braking to stop short of the crossing plow, NTSB said.
Jeffrey Leib: 303-954-1645 or jleib@denverpost.com
