When air traffic controllers realized the planes' flight paths intersected and the jets were about to collide, they ordered the Learjet to abort its landing and fly around the airport again. The American Eagle ERJ-145, a regional jet, was instructed to stay low on departure.
The board said the Learjet passed "325 feet above and slightly behind" the departing the American Eagle jet.
At the high rate of speed the two planes would have to have been traveling and the narrowness of the distance they came from each other, "There is no margin of error or safety there," said Ken Mead, a former Transportation Department inspector general. "It's almost random chance they don't hit each other when they get that distance."
The runway the Learjet tried to land on had been closed to landings moments before the incident, said Federal Aviation Administration spokeswoman Lynn Tierney. The smaller jet passed just above and behind the American Eagle plane as that plane was taking off, she said.
Takeoff and landing procedures at O'Hare have been changed as a result of the incident, she said.
"The changes have to do with intervals at which planes will be accepted onto those particular runways," Tierney said.
The NTSB is also investigating two similar near collisions at John F. Kennedy International Airport in New York.
On July 11, a Delta Air Lines Boeing 757 landing at JFK nearly collided with a Comair regional jet taking off on another runway when the pilot decided to abort the landing and execute a "go-around" - a routine procedure often used during heavy congestion - bringing the airliner into the flight path of the smaller jet.
A week earlier, on July 5, a Cayman Airways Boeing 737-300 and a LAN Chile Boeing 767-300 also nearly collided. In both instances, controllers were able to send the planes off on divergent headings. The JFK near collisions involved nearly simultaneous takeoffs and landings on perpendicular runways.
Over the last few months, federal authorities have investigated go-around procedures at airports in Newark, Memphis and Detroit, all of which use perpendicular runways similar to JFK's. Controllers claim these procedures can put a plane performing a go-around directly in the path of a plane taking off on a perpendicular runway.
