CHICAGO - The Federal Aviation Administration on Tuesday eased up on imminent plans to revise airport procedures aimed at reducing the risk of an arriving airplane flying over or landing on top of another plane waiting on a runway to depart.
The changes, which the National Transportation Safety Board had recommended to the FAA over the past six years, were announced last week and had been set to begin March 20, during the peak of the spring-break travel period.
The proposed tightening of rules governing how planes line up at airports for takeoff would appear to help prevent a rare type of accident that could cause hundreds of deaths in a single collision.
The FAA notice to airport air-traffic control towers last week said mistakes are continuing to occur involving planes taxiing onto an active runway when an approaching plane is about to land on the same runway or an intersecting runway.
On Feb. 17, a controller at Los Angeles International Airport directed three aircraft to use the same runway, the FAA said. A departing SkyWest turboprop was cleared to use a runway on which a Southwest Airlines Boeing 737 was about to land. The controller also cleared an Air Canada jet to cross the other end of the same runway.
Other incidents have occurred in recent years in Salt Lake City, Fort Lauderdale, Fla., and at Midway Airport in Chicago, officials said.
But the FAA, reacting to related safety issues and concerns about flight delays ballooning, on Tuesday told the airlines and air-traffic controllers' and pilots' unions that it would grant at least temporary waivers from the new rules, starting with the nation's 35 busiest airports.
The FAA won't force airports to change their takeoff procedures, "but by March 20 airport towers will have to explain to us why they want to continue using it," said Russell Chew, the FAA's chief operating officer.
As a result, no immediate changes are expected to occur at O'Hare International Airport, Midway Airport or Mitchell International Airport in Milwaukee, officials said. But several hundred medium-sized and smaller airports could lose an air-traffic tool they have used to keep flights bound for the larger airports on schedule.
The controllers union said the FAA's planned change would add to congestion at already crowded airports, reducing arrival and departure rates by as much as 20 percent.
Under existing rules, a plane that is No. 2 in line for departure is permitted to taxi onto the runway and stop as soon as the plane in front starts its takeoff roll. Once the first plane is airborne and at least 6,000 feet down the runway, the second plane begins its takeoff roll and the next plane in line on the taxiway moves into takeoff position on the runway.
Air-traffic controllers call the procedure "locked and loaded," because it facilitates launching planes at tight intervals and keeps airports running efficiently.
Under the revisions the FAA was set to impose, planes in the No. 2 departure position would not be permitted to begin taxiing onto the runway until after the plane taking off in front is airborne.
The controllers' union, the National Air Traffic Controllers Association, contends the FAA over-reacted to a small number of high-profile cases in which human error caused arriving and departing planes to get perilously close to each other.
Controllers said the FAA's fix could unintentionally intensify risks on runways that are used for landings and takeoffs. Such a scenario would involve a controller directing a plane waiting on a taxiway to proceed to the runway for takeoff while an approaching plane is still five miles from touching down. A miscommunication between controller and pilot, or a delay in the plane entering the runway, could lead to a close call between the arriving and departing planes, potentially even a fly-over incident that could lead to a crash.
"You almost must already have the pilot on the runway in position so he is ready to roll when you tell him to," said Doug Fralick, director of safety and technology at the controllers union. "If the plane is still sitting on the taxiway, you lose your predictability because it takes time for the engines to spool up power and the plane to get into position."
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