FAA downgrades safety violation over D.C. area skies
Sunday, July 11, 2010
A business jet crossed into the potentially dangerous wake turbulence of a United Airlines flight bound for Europe on Tuesday in what the Federal Aviation Administration initially recorded as the 23rd operational error this year by the region's air traffic controllers.
The FAA acknowledged that a mistake caused the smaller plane to violate safe-distance requirements, but the agency said that after further review, the incident was downgraded from an "operational error" to a less serious "proximity error."
Turbulence left by a massive Boeing 777, which weighs up to 328 tons on takeoff, can be likened to waves created by a large ship moving through still water. It ripples through the air well after the plane has passed. And just as the wake of a ship can capsize surrounding boats, air turbulence can endanger nearby aircraft and, in the most-serious incidents, cause them to crash.
Wake turbulence from a Boeing 767 landing at Mexico City's airport was cited by investigators as the cause of a 2008 Learjet crash that killed Mexico's interior secretary and 15 other people.
"Wake turbulence encounters are a very real concern and one of the few separation standards we have that are based on science," said an FAA staff member familiar with Tuesday's incident. The staff member asked not to be named for fear of losing his job.
"For the layman, the controller's mistake put the [small plane] at risk of encountering dangerous wake turbulence left behind by a departing heavy jet," the staff member said. "The two aircraft were not in danger of colliding. The real issue is the controller forgetting to turn aircraft."
An internal FAA document, the Administrator's Daily Alert Bulletin, distributed to air traffic control supervisors Thursday said the small plane "crossed the course" of the United flight, violating the required separation between aircraft of 1,000 feet in altitude and three miles in distance.
The ripple effect from the Boeing 777 is so great that FAA regulations are even stricter to protect small aircraft from its "wake remnant." Minimum distances are five miles behind, 2,500 feet on either side and 1,000 feet below.
The Cessna Citation 550, with a maximum takeoff weight of about 15,000 pounds, came within 2.79 miles and 800 feet of the larger jet.
The second look
In response to an inquiry, the FAA on Friday underscored its belief that the air space violation did not involve a most-serious, "category A" operational error, as initially described in an agency internal document.
"After reviewing initial information, data and radar tracks, the FAA determined that no operational error occurred," the FAA said in a statement. "The two aircraft maintained nearly 100 percent of required separation standards. The review indicated the air traffic controller directed the smaller aircraft away from the wake turbulence of the Boeing 777 aircraft."
FAA supervisors who review errors are permitted to downgrade a controller's mistake to a "proximity error" if the no-fly separation zone is violated by less than 20 percent. But under FAA rules, they are prohibited from doing so if the encounter involves wake turbulence.