New math adds up to better landings

Starting next year, a better mathematical model will enable the Federal Aviation Administration to guide pilots during landings in poor visibility with a level of precision that was not anticipated until 2005.

In December 2003, the FAA planned to offer guidance down to 350 feet to planes equipped for the Wide Area Augmentation System (WAAS), a network of ground stations that correct satellite signals and broadcast them to receivers on aircraft.

Raytheon Co. is set to deliver the system at that time, but with an enhancement that will enable pilots to descend to an altitude of 250 feet. The FAA had not expected to offer that level of precision approach until two years later.

The agency enhanced WAAS' capability using a mathematical model, recently developed by Mitre Corp., to create a new landing procedure.

There's a double benefit to the enhancement: the ability to land in worse weather and better access to airports, said Vince Massimini, a principal engineer at Mitre.

Using its own computer modeling program, Mitre created new criteria for WAAS that narrow the horizontal limits for an approach, making it less likely that a plane's path will intersect an obstacle, such as a building or a tower. Its work to improve the system is ongoing, according to Massimini.

WAAS enhances information supplied by the Global Positioning System, which uses satellites to enable airborne, land and sea users to determine their positions anywhere in the world.

Unlike most commercial jets, which have instrument-landing systems, many smaller aircraft are unequipped to deal with landing in bad weather. WAAS aims to guide pilots of such aircraft close enough to the ground — even in zero-visibility conditions — to see the airport and continue descending.

"The advantage is safety," said Tammy Jones, a spokeswoman for the FAA. "As you lower the minimums, we're getting an even clearer view."

To use the enhanced system, special equipment — estimated at $5,000 to $10,000 per plane — will be needed.

"It's certainly a worthwhile benefit for WAAS users," said Bill Sears, director of communications, navigation and surveillance at the Air Transport Association, a trade organization for the airline industry. "It makes sense to fine-tune WAAS and get as much out of it as they can."

"We think that WAAS has a potential to be a very significant enhancement to air traffic service," said John Mazor, an Air Line Pilots Association spokesman.

The enhancement means that in inclement weather some aircraft should be able to land that otherwise would be diverted. "We've been anxiously awaiting it," Mazor said. "It has been dragging on for some time."

Looking ahead, the FAA issued a request for information March 15 on its plans to expand satellite services for WAAS. Comments are due by April 2, and the agency expects to award a new contract for the services sometime in fiscal 2002.