A United Express flight from Denver to Casper — at the direction of an air-traffic controller — descended close enough to the ground Sunday night to set off a collision warning.
The pilots of the 36-seat commuter plane pulled the aircraft up to avoid hitting high terrain, according to air-safety officials.
The controller at the Denver Air Route Traffic Control Center in Longmont directed flight 7105 to descend to 8,000 feet in an area where the minimum altitude under instrument flight rules is 10,500 feet, said Lyle Burrington, president of the National Air Traffic Controllers Association unit at the radar center.
The minimum safe altitude is set 2,000 feet above an area’s highest terrain, Burrington said.
The National Transportation Safety Board is investigating the incident. The United Express plane, operated by Mesa Airlines, had 23 passengers aboard.
The commuter plane came within 600 to 900 feet of the ground before the alarm warned pilots, according to the Federal Aviation Administration.
The incident, which occurred about 10:45 p.m., was the second operational error by a controller at the air-traffic control center Sunday night, FAA officials said.
Earlier, another controller apparently was unaware that pilots of a plane flying from Grand Junction to Lincoln, Neb., had filed a flight plan with a turn once they reached a navigational fix in the skies over western Colorado.
3.1 miles from jetliner
When pilots made the turn, the plane came within 3.1 miles laterally and 700 feet vertically of a United Airlines jet flying at 38,000 feet from Denver International Airport to the Los Angeles area, Burrington said.
For high-altitude flights, an operational error is recorded if planes get closer than 5 miles to each other laterally or 1,000 feet vertically.
The controller involved in the Casper incident had worked from 6:30 a.m. to 2:30 p.m. on Sunday and then returned to the Longmont facility for a 10:30 p.m. to 6:30 a.m. shift, Burrington said.
“Due to staffing, we’ve been doing eight-hour turnarounds for awhile, but it’s not optimum. Controller fatigue is an issue we’ve been raising,” he said. “We don’t have enough controllers to fully staff the sectors.”
Senior managers at the Longmont center say the facility is “well within its staffing ranges,” FAA spokesman Mike Fergus said Tuesday.
More training ordered
The controller involved in the Casper incident will undergo “extensive skill enhancement training,” Fergus said.
The controller involved in the earlier incident also will undergo retraining, he added.
The Longmont center handles high-altitude traffic for a multistate area with Colorado in the middle. The center’s controllers also direct low-altitude traffic to smaller airports.
Burrington, a controller for nearly 19 years, said the Longmont facility currently has 248 fully certified controllers now, compared with 261 a year ago.
By the end of September, he said, another 54 certified controllers are eligible to retire.
Jeffrey Leib: 303-954-1645 or jleib@denverpost.com
