Air traffic controllers have made more mistakes at Minneapolis-St. Paul International Airport than at many of the nation's largest airports, including some that are busier, federal records show.

A third of the Minneapolis-St. Paul errors came in the two most serious categories, including a near-collision last year between a US Airways flight with 90 passengers and a cargo plane.

The errors from 2007 through 2010 exceeded those at airports in Los Angeles, Detroit, Denver and Phoenix -- each of which logged more arrivals and departures.

The Minneapolis-St. Paul airport also had more errors than some airports where air traffic is considered harder to manage, including New York's LaGuardia, Boston's Logan and Reagan National near Washington, D.C.

The 21 errors at Minneapolis-St. Paul were among thousands of air traffic control mistakes reported nationwide to the Federal Aviation Administration and obtained by the Star Tribune in a Freedom of Information Act request.

Without commenting specifically on the frequency of errors at Minneapolis-St. Paul, the FAA said it is "reviewing procedures and training throughout the air traffic control system." The FAA said it "takes all errors seriously."

Current and former controllers say there is no clear explanation for the higher number of errors, though some pointed out the positioning of the airport's runways.

"I'm trying to think of a reason why Minneapolis would be a more difficult airport," said Bill Voss, a former FAA official and air traffic controller and president of the Flight Safety Foundation, a nonprofit that promotes air travel safety worldwide. "What's up?"

'Sometimes just bad luck'

Rob Kelzenberg, a controller at the Minneapolis-St. Paul tower, said a requirement for staggering planes on their final approach to the parallel runways contributed to a few errors. But he said that alone doesn't explain why Minneapolis-St. Paul would have more errors than other airports.

"Sometimes just plain bad luck falls into it," Kelzenberg said.

Three-fourths of the Minneapolis errors involved airborne planes, and the rest occurred on the ground.

Besides the 2010 episode involving the US Airways flight, rated the most serious category "A," there were six category "B" errors at MSP. They are among four categories of errors that describe how close planes come to each other.

"Everybody ... needs to take it seriously and do everything they can to try to bring this number to zero," said airport spokesman Pat Hogan.

Reports released by the aviation agency describe misunderstandings by controllers juggling flight assignments.

• Shortly after a Pinnacle Airlines CRJ regional jet was instructed to take off and make a left turn, a controller "did not remember the coordination" and cleared a Northwest Airlines flight to take off on a similar route. The Northwest pilot "reported ... they were leveling off ... to stay below the CRJ."

• A controller "mistakenly instructed" a Northwest pilot to turn right after takeoff, instead of ordering a trailing regional jet flight to do so. Thirteen seconds elapsed before the controller gave the order to the airborne regional flight, but by then its pilot wasn't listening and "didn't appear to be turning as instructed."

• A controller "misidentified the location" of an aircraft crossing a runway before clearing a Northwest flight to take off on it. The tower employee was "alerted to the crossing traffic by another controller." The Northwest pilot "had just started his takeoff roll ... and stopped after approximately 300 feet."

• A Northwest plane came too close to a smaller craft near Flying Cloud Airport in Eden Prairie. "Factors that created a distraction were an emergency in progress and a go-around" -- a canceled landing on another runway.

• A control tower trainee was unaware of the departure of a Northwest flight when he instructed a SkyWest plane to make a similar departure off a parallel runway, and the two planes came too close together.

'Always scan other runway'

The National Transportation Safety Board's final report in May on the most serious error, the US Airways mishap, illustrates the intense pressure facing controllers and some lessons learned.

While earlier news accounts focused on a single error, the report said two separate errors caused the planes to twice get too close after takeoff.

It was shortly after dawn on Sept. 16, 2010, when the US Airways Airbus and Bemidji Aviation cargo plane were departing from parallel runways 30L and 30R, the busiest at MSP.

Two controllers -- one for each aircraft -- told them to turn left after takeoff. The Airbus turned, but the cargo turboprop continued flying straight. The jet's collision avoidance alarm went off.

"The first officer responded with a swift pull-up," said a report from an unidentified US Airways crew member. "Within just a few seconds, I heard the whine of turboprops go under our aircraft."

An estimated 50 feet separated the planes.

"Why didn't you start the turn once you were airborne?" one controller asked the cargo plane.

"Sorry about that," replied its pilot.

The NTSB said the cargo pilot contributed to the near-collision, but it also blamed one controller for ordering the Airbus to make the turn without establishing the position or direction of the cargo plane. The agency said the other controller wasn't paying enough attention to the cargo plane after a third aircraft landed on the same runway and its pilot asked for directions.

"The controller stated that he became distracted ... and was not watching [the cargo plane]," the NTSB reported.

The second error happened about two miles northwest of the airport when one of the controllers instructed the cargo plane to turn left once more. "This instruction again put the two aircraft into conflict," the report said.

Both controllers are longtime FAA employees. The controller in charge of the Airbus was asked how he would now handle the situation differently.

"He stated that when he trains other controllers, he tells them they should always scan the other runway for traffic," the NTSB report said.

While the US Airways episode made news, a more recent mistake involving the two runways didn't. On Nov. 11, 2010, a Delta Air Lines Airbus and a Mesaba Airlines turboprop were told to take off in the same direction and turn left "without ensuring adequate separation," the NTSB reported. The error was too recent to be included among the 21 reported by the FAA.

Closer runways?

The agency in recent years phased in a policy encouraging controllers to identify errors voluntarily, but it doesn't explain the higher number of reports at MSP than at some other major airports.

Kelzenberg said the parallel runways at Minneapolis-St. Paul are closer than runways at some other airports and require planes to maintain a 1.5-mile staggered distance when landing. Four of the 21 errors at MSP came when planes slipped within that distance.

"It may be a piece of it ... not quite enough to explain all of it," said Voss, who spent 23 years at the FAA specializing in air traffic management.

He said other factors made Minneapolis-St. Paul less challenging than LaGuardia, Boston Logan or Reagan National. He called National "a hideously complex operation." If those airports are seeing fewer errors than MSP, he said, "I'd have to wonder why."

Pat Doyle • 612-673-4504