The Federal Aviation Administration (FAA) this week relaxed its rule on the required separation distances for aircraft flying behind the massive Airbus A380.

However, the giant double-decker jet still requires greater distances than Boeing's largest airplane, the new 747-8 jumbo.

Planes must keep a certain distance behind other jets to avoid turbulent air from the wake of the airplane ahead. The bigger the airplane. the greater the potential turbulence. And the impact of turbulence on smaller airplanes will be greater than on larger planes.

The FAA classifies the A380, which has a maximum takeoff weight of 600 tons, as "super heavy." The Boeing 747-8, at 493 tons, is classified as "heavy."

On Monday, the FAA ruled that airplanes must fly at least 5 miles behind the A380 while cruising.

On approach to an airport, the required separation distances behind the A380 are 8, 7 and 6 miles, respectively, for "small" airplanes (such as business jets); "large" planes (such as a 737); and for "heavy" planes (such as the 767 or 747).

Previously, the required separation for small, large and heavy aircraft behind an A380 were 10, 8 and 6 miles.

Airbus spokeswoman Mary Anne Greczyn said the FAA's relaxation of the rule "finally brings the separation distances for the A380 in the U.S. in line with International Civil Aviation Organization (ICAO) recommended guidelines that have been in effect for several years."

The FAA has set the separation distances for small, large and heavy aircraft behind a 747-8 at 6, 5 and 4 miles.

Shorter separations speed up aircraft traffic flow at airports by allowing landings to be closer together.

Dominic Gates: 206-464-2963 or dgates@seattletimes.com