The rate of close calls on airport runways in the United States is up over last year and the risk of a collision is high, a U.S. government investigator said Thursday.

Gerald Dillingham, the General Accountability Office's top expert on aviation safety, told a House of Representatives panel that there were 24 of the most serious kinds of runway incursions — defined as an event in which any aircraft, vehicle or person intrudes in space reserved for takeoff or landing — in fiscal 2008.

That's the same number of serious incursions as last year. But since air travel and airport operations have declined this year, the rate of serious incidents — measured by number of incidents per one million takeoffs and landings — has increased about 10 per cent, Dillingham said.

Both the number and rate of all types of runway incursions, ranging from near collisions to minor incidents in which there was no threat to safety, also are up, he said.

"We all agree … that [the Federal Aviation Administration] has given a higher priority to runway safety," including following several GAO recommendations, Dillingham said. "Despite these actions the risk of runway collisions is still high."

Serious incidents down from high of 53 in 2001

FAA Chief Operating Officer Hank Krakowski said the agency has made "solid progress" this year. He noted that the 24 serious incidents in 2007 were down from a high of 53 incidents in 2001.

Runway incursions are a top safety concern internationally and among U.S. air safety officials. The deadliest disaster in commercial aviation history was a runway incursion in 1977, when 582 were killed in the ground collision of two Boeing 747s at the Tenerife airport in the Canary Islands.

Since 1990, 112 people have died in seven U.S. runway incursions, according to the National Transportation Safety Board.

In December, the GAO warned that air travellers face a high risk of a catastrophic collision on U.S. airport runways because of faltering federal leadership, malfunctioning technology and overworked air traffic controllers.

Dillingham and Krakowski agreed that mistakes by pilots and controllers rather than technology problems were key factors in many incursions.

The most recent serious runway incursion occurred last week at Lehigh Valley International Airport in Allentown, Pa. A United Express flight with 60 passengers had to brake and swerve, avoiding by about three metres a small plane that had landed ahead of it on the same runway.

The National Air Traffic Controllers Union said a trainee in the airport's control tower mistakenly thought the Cessna had left the runway and cleared the United Express flight for takeoff.

With files from the Associated Press