By Don Phillips
Washington Post Staff Writer
Washington Post, Friday, January 4, 2002; Page A14

The Federal Aviation Administration will launch a new satellite-guided landing system at Reagan National Airport to allow properly equipped airliners to land in weather that now would force them to bypass the airport.

The plan was developed before the Sept. 11 terrorist attacks and is intended mainly to increase airport capacity in poor weather, but FAA officials said it also could become the core of a security enhancement to allow the FAA, the Secret Service and the military to more closely track airliners approaching National down the Potomac River past the White House.

"This had nothing to do with 9/11, but I would think the Secret Service would want to know about it," said Nicholas Sabatini, the FAA's associate administrator for regulation and certification. The system would send aircraft down a much more precise path toward the end of runways, he said.

The Secret Service, citing security concerns, initially wanted to close National after the terrorist attacks. The White House decided to allow the airport to reopen if there were sky marshals on every flight in and out of the airport and if the FAA adopted new security and navigational procedures, including a new "downriver" approach path. The planned satellite system has the capacity to more tightly limit planes to that new, straight-in path.

The FAA estimated that the system will be ready for use in less than six months. National would become one of the first major U.S. airports to use the satellite-guided procedures, and Sabatini said the FAA would consider it an example for other large airports to follow.

The system requires no new ground equipment at National, but airplanes landing there would need the proper equipment to use it.

Arlington-based US Airways, which already has the equipment on its fleet of Airbus A320s and uses the satellite-guided procedure at other, smaller airports that often don't have instrument landing systems, is the lead airline in the FAA's plan to install the system at National. Alaska Airlines is providing technical support because it uses the system at many airports in Alaska.

The procedure, called required navigation performance, or RNP, is tailored to each airport. It blends signals from global-positioning satellites with information from ground- and air-based navigation systems and sensors such as aircraft inertial guidance systems, ground-radio navigation aids and instrument landing systems. The system cross-checks each input against the rest, meaning that no one system can fool the onboard equipment that blends all the information. The increased precision allows pilots to land even in zero-visibility weather at airports with no instrument landing systems.

Alaska Airlines uses the system on one of the most treacherous approaches in the world, between two strings of high mountains into Juneau from the south.

"It was eye-opening," Alaska pilot Spud Harper said last year as he and co-pilot Scott Olson monitored the system that was guiding their Boeing 737-400 through a thick layer of clouds down the Gastineau Channel approach to Juneau. "At first, pilots are always skeptical."

Olson, the pilot flying that leg of the trip, occasionally held his hands in the air to demonstrate that the satellite system was guiding the plane through the autopilot. The crew monitors the system, but the system flies the plane.

Although the National downriver approach is not as as spectacular as Juneau's, Sabatini said the National system will allow airliners to stick to a much narrower course than with current landing systems. That means that planes equipped to use the new system can descend lower at an earlier point in their flight path rather than remain high until they pass obstacles such as the high-rise buildings in Rosslyn.

This would give planes a lower "decision altitude" for National's Runway 19, which runs from north to south. Currently, a pilot landing in poor visibility must break off the landing and "go around" if the ground is not visible when the plane is 720 feet high. Using the new satellite system, the decision altitude would be reduced initially to 565 feet and eventually to 250 feet.

Using National's current landing system for Runway 19, planes approaching on instruments are guided horizontally by a radio beam that fans out at an angle of five degrees from a point near the end of the runway. That means that planes five, 10 or 15 miles out have wide horizontal latitude and must remain high above any obstacle within that large area.

Under the planned satellite procedure, planes would approach along a straight, relatively narrow path. Initially this path would be 0.6 miles, and eventually it would narrow to 0.22 miles.

"This would be a tighter, much more precise approach," Sabatini said.

Airlines could continue to use current systems to land at National in good weather. When weather worsens, landings first would be shifted to Runway 1, approaching from the south. If winds preclude the use of Runway 1, then the satellite system would guide the approach to Runway 19 as the final alternative. Under the FAA's runway designation system, based on the compass direction of landing or takeoff, Runway 1 and Runway 19 are the same runway.

Such satellite-guided approaches could revolutionize aviation safety worldwide, particularly in South America, Africa and other areas of the world where instrument landing systems are rare.

The FAA's costs for implementing the procedure at National are negligible, limited mainly to writing air traffic control procedures. Some airports, though, would require minimal ground equipment, such as several mountaintop wind sensors at Juneau.

Pam Hamilton, manager of air traffic and navigation technology for US Airways, said all new Airbus and Boeing aircraft are now fully equipped out of the factor. Older aircraft can be equipped for a price, but Hamilton said US Airways has no plans to equip its older aircraft, which it is phasing out anyway.

The procedure could be expensive for some airlines with older planes, particularly if the military or the Secret Service were to require it. Airlines could still use current landing systems, but they would still be stuck with the old decision altitudes, meaning that competitors with properly equipped aircraft could land when others couldn't. This would exert economic and competitive pressure to either equip their planes or use newer planes into National.