Air traffic controllers working at Denver International Airport knew a small Mitsubishi cargo plane was flying too low a little more than a minute before it crashed near Centennial Airport last August.
But the DIA facility didn’t have the ability to sound a warning in Centennial’s tower to alert the pilot until it was too late, air safety officials said.
The MU-2B-60 turboprop was flying an instrument approach to Centennial in rainy weather a little after 2 a.m. on Aug. 4 when it hit a ridgeline about 4 miles south of the airport. The sole pilot was killed.
On Tuesday, the National Transportation Safety Board issued a safety bulletin highlighting 11 aircraft accidents around the country – including the Centennial crash – that it linked to problems with the minimum safe-altitude warning (MSAW) and conflict-alert systems.
The Federal Aviation Administration’s computerized systems are used to alert controllers when planes are in danger of striking the ground, obstructions such as radio towers or other aircraft.
The NTSB said FAA controllers at the radar center near DIA got a warning sound and an on-screen alert that the Mitsubishi was flying too low.
Yet because of the FAA software problem, the DIA facility could not transfer audible warnings to Centennial tower controllers until planes were within 5 miles of the Arapahoe County airport, the NTSB said.
On Aug. 4, the alarm sounded at Centennial when the Mitsubishi reached the 5-mile mark; within five seconds, the controller warned the pilot: “… Check altitude. … You appear to be well below the glide slope.”
There was no answer from the pilot, and the plane hit the hill, at an elevation of 6,350 feet, about two seconds later, the NTSB said.
“Aural alarms are particularly important in tower facilities because controller attention must mainly be focused on aircraft visible through the windows, rather than on the radar display,” the agency said in its report.
The NTSB urged the FAA to fix the software problems and redesign altitude-warning and conflict-alert systems so “they reliably capture and direct controller attention to potentially hazardous situations.”
FAA officials had not had time to evaluate the recommendations and could not comment on them Tuesday, FAA spokesman Allen Kenitzer said.
Centennial executive director Robert Olislagers said Tuesday that he had not been briefed about any changes in control procedures that might correct the gap in notification.
But Sharon Wilkins, the FAA tower supervisor at Jefferson County Airport, said the agency recently altered its rules to require controllers at the DIA radar center who get low-altitude alerts on Jeffco flights to call her tower as a backup.
“It’s an extra layer of safety,” Wilkins said, noting that Jeffco controllers get frequent low-altitude alerts because of the rising terrain so close to the airport.
“Every time that alert goes off” at the DIA radar center, controllers “are required to call us,” she said. “We look out and see it, and say, ‘Roger, it’s still airborne.”‘
Staff writer Jeffrey Leib can be reached at 303-820-1645 or jleib@denverpost.com.
