Precision landing, less time circling the airport

Capt. Mike Adams demonstrated what the future will look like at airports in the United States as he pulled back on the throttles of his Boeing 737 flight simulator, setting the engines on idle to glide smoothly from his cruising altitude all the way down to the runway.

Starting in June, that's exactly what Alaska Airlines flights will be doing when the carrier begins testing the use of satellite technology to land at Seattle-Tacoma International Airport - all in the hope of saving fuel and reducing delays.

Alaska Airlines, one of the smallest carriers in the United States, has taken some of the biggest steps in adopting a technology that allows its planes to navigate Alaska's hazardous terrain, weaving through narrow valleys and past mountain peaks to land at remote airports in some of the worst imaginable weather. It now wants to demonstrate that the same technology can also work at big, busy airports, said Capt. Adams, the airline's chief technical pilot.

Planes using the new technology will cut 30 miles, or 48 kilometers, from their approach by taking a more direct path to the runway. They will no longer need to circle overhead awaiting clearance to land. And pilots will not have to push and pull at the throttles to maintain the altitude assigned by air traffic controllers as they begin a stairlike descent.

''This makes much better use of the airspace,'' Capt. Adams said ''It improves efficiency and reduces congestion. That's the holy grail we're all aiming for.''

In Europe, a satellite-based precision landing system has been fully operational since February, according to Eurocontrol, the agency based in Brussels that coordinates air traffic management across the region.

But the Seattle experiment marks one of the first extensive applications of satellite technology in the United States after years of planning and political wrangling in Washington.

Replacing the radar-based air traffic control system, which the nation's airports have relied on since the 1940s, is an enormous and expensive undertaking. By one official government estimate, the price could reach $42 billion by 2025.

But the agency in charge of the program, the Federal Aviation Administration, has been hamstrung by political infighting that deprived it of a stable budget for five years. Congress finally approved a four-year budget in February, including $1 billion a year for the program, called the Next Generation Air Transportation System, or NextGen.

The program has already been beset with trouble. A government audit found in February that half of the 30 critical contracts needed to build the new system were delayed, and more than a third were over budget.

And the airlines complain that the F.A.A. has been slow to create new landing procedures that make the most use of satellite guidance. It takes 5 to 10 years to create these procedures because of lengthy environmental and noise impact studies, and the difficulty of coordinating flights in busy airspaces. The F.A.A. is now trying to speed up that process to three years.

The agency has approved tests using satellite-guided landings at Phoenix Sky Harbor International Airport, and experiments are planned this year in Washington; Atlanta; Charlotte, North Carolina; and Dallas. Delta Air Lines, Southwest Airlines, JetBlue and American Airlines have all been trying out various aspects of satellite navigation.

Given the expected growth in air traffic in the next decades, airlines and regulators say there is an urgent need to modernize the existing air traffic control system. The F.A.A. projects that the number of planes flown by domestic airlines will double in the next two decades, while the number of domestic passengers will reach one billion by 2024, up from 732 million this year. Much of that growth will be concentrated in the biggest airports, most of which are already congested.

Radar has proven to be reliable over the years. But air traffic controllers can be sure of the precise location of any single plane they are directing only when their radar sweeps across it - once every six seconds. To make up for that uncertainty, controllers keep wide buffer zones between flights. Satellite technology will eventually change that equation and allow planes to fly much closer to one another because they will broadcast their locations with more accuracy.

In effect, airports could increase capacity without building more runways because more planes could take off and land every hour.

For airlines, more efficient approaches and landings could mean significant fuel savings. The F.A.A. projected that airlines using Hartsfield-Jackson International Airport in Atlanta, one of the world's busiest, would fly 1.2 million fewer miles each year, saving as much as 2.9 million gallons of fuel a year and allowing an additional 10 planes an hour to take off.

But NextGen has also been slowed by disagreements between the airlines and federal regulators over which would foot the bill. Equipping a single plane with a GPS system can cost more than $340,000. That quickly adds up for airlines with hundreds of planes in their fleet, and with no immediate payoff for the upgrade. New planes have the technology, but older models must be retrofitted.

That is the sort of logjam that the Seattle experiment is seeking to break. It will use something called Required Navigation Performance, or R.N.P., which is like GPS in cars. The difference is that the plane's autopilot feature can guarantee that the flight will stay precisely on course, from takeoff to landing, even in bad weather or turbulence.

''Today's planes are a lot smarter than a lot of the equipment on the ground,'' said Sherry Carbary, the vice president of Boeing Flight Services. Alaska Airlines has used satellite-navigation for its planes since 1996 in Juneau, where bad weather had often forced flights to be canceled or diverted to Anchorage.

The airline has spent $40 million in the past decade on both technology and pilot training. But it estimated the technology is saving $15 million to $20 million a year in allowing takeoffs and landings that would have been impossible before.

The shift from radar to satellite navigation is similar to the move from analog to digital television, said Capt. Adams, the Alaska Airlines pilot, and will allow more information to be shared through digital channels in the future.

Airplanes, for instance, may be able to share weather conditions they encounter during flight, including wind speeds or even turbulence, and automatically relay that information to other planes. The data is currently recorded by each plane but is not shared.

In the future, another step could be to manage the timing of landings. A plane taking off from Los Angeles, for instance, would be given a precise landing time in Seattle. Its flight computer would then manage the best speed, altitude and flight path to ensure that the plane lands on time.

''The benefits of R.N.P. can be applied elsewhere than just Alaska,'' Capt. Adams said. ''The tools we use today for terrain can be used anywhere in the world to ease traffic congestion.''