FAA requires extra distance behind Boeing's 787 and 747-8

The Federal Aviation Administration has issued an interim requirement that planes landing after either of Boeing's two new airplanes, the 787 Dreamliner and the 747-8 jumbo jet, stay at least 10 miles behind.

The current requirement for large airplanes, including the 747-400 now in service, is just 4 miles separation from other heavy jets and up to 6 miles from light aircraft.

The FAA said the requirement will ensure that other airplanes are not subject to "wake turbulence," which is a severely disruptive air flow that is generated at the wingtips of big airplanes and swirls backward in a spiraling vortex.

"Studies indicate that wake vortices generated by the B747-8 and possibly by the B787 (all variants) may be more substantial than those of aircraft in the 'heavy' wake turbulence category," the FAA ruling states.

If the rule were to become permanent, the lengthy separation from other planes would be a major problem for airlines operating the new Boeing jets.

It would reduce the number of airplanes that could fly into a congested airport and add to flight delays.

However, this is not the final standard.

The FAA termed the interim standard "conservative," and said final guidance will be issued after 787 and 747-8 flight tests are completed and evaluated.

Boeing expects to complete flight tests on the Dreamliner in time for an initial delivery to All Nippon Airways by mid-February.

The 747-8 won't be delivered until mid-2011.

The FAA said the interim standards are based in part on guidance received from the international regulatory organizations that studied the wake vortices of the Airbus 380-800 in 2006.

In general, the bigger and heavier the plane, the greater the wake turbulence.

In 2006 the International Civil Aviation Organization issued a 10-mile separation standard for the A380 superjumbo jet.

This was later relaxed, but a separation of 6 to 8 miles is still required for the A380, depending on the size of the aircraft behind it.

The 747-8, though heavier than the 747-400, is 21 percent lighter than the A380. And the 787 Dreamliner's maximum takeoff weight is just over half that of the 747-8.

Furthermore, the FAA ruling states that modeling suggests 747-8 wake vortices are similar to those created by the 747-400.

That suggests the final standards for the new Boeing airplanes may be closer to the current 747-400 standard 4-to-6-mile separation from other airliners.

In the meantime, the federal ruling, which was first reported Monday on the website of The Wall Street Journal, takes effect Nov. 1.

"The only thing we can say is that we are discussing it with the FAA," said Boeing spokeswoman Lori Gunter.

Sixth Dreamliner

makes first flight

The sixth and final Boeing 787 Dreamliner flight-test airplane had some maintenance trouble on its maiden flight from Paine Field on Monday, and diverted to Boeing Field instead of flying on to Moses Lake as scheduled.

The pilot decided to curtail the flight "as a precautionary note," said Boeing spokeswoman Yvonne Leach.

The crew received a "maintenance message" during the flight, meaning that some warning flag was raised in the cockpit.

Leach declined to provide details; she said the flight was "still considered a success."

This Dreamliner is one of two test planes with General Electric engines; the other four are powered by Rolls-Royce engines.

It will perform tests specific to certification of the GE-powered 787s, including flying for extended periods with one engine shut off and measuring the noise generated around airports on takeoff and landing.

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

This story was originally published Oct. 4, 2010, and corrected Oct. 5, 2010. The story was updated to correct erroneous information from the FAA concerning the weight of the Boeing planes.