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 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,” a severely disruptive air flow generated at the wingtips of big airplanes that swirls backward.
“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.
The FAA termed the interim standard “conservative” and said final guidance will be issued after 787 and 747-8 flight tests are completed and flight test data have been 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 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 super-jumbo 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 following aircraft.
The 747-8, though heavier than the 747-400, is 27 percent lighter than the A380. And the 787 Dreamliner’s maximum take-off weight is approximately one-third 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 FAA ruling, which was first reported Monday on the Web site 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.
