SEATAC– Long after dark one night last week when few planes were in the air, an Alaska Airlines Boeing 737 descended toward Seattle-Tacoma International Airport its engines at idle power. Aboard were Alaska pilots and technicians and officials from the Federal Aviation Administration’s Washington, D.C., headquarters.
The occasion was the latest test of an experimental landing procedure at the airport that promises to save millions of gallons of fuel, lessen jet noise, cut pollution and save airlines precious dollars.
The new procedure, dubbed optimized profile descent by the airline industry and its regulators, is a measure that uses high-technology satellite-guided navigation, combined with the power of computerized aircraft flight management computers and the oversight of the FAA to change the decades-old procedures for bringing aircraft from cruising altitude to a landing on the runway.
The technology is 15 years old, but it has never been applied so completely in a complicated urban airport setting with all of its airspace conflicts, political considerations and airborne traffic jams.
SeaTac-based Alaska, for instance, has used satellite-based navigation systems since 1994 to help navigate its aircraft to landings at many of its terrain- and weather-challenged Alaska airports. Couple that navigation with computerized flight management systems, and aircraft can calculate and execute flight paths that will deliver an aircraft from cruise altitude to the runway threshold on a smoothly descending path that requires only minimal engine thrust.
Under the landing procedure in use now, once an aircraft descends to 10,000 feet, it follows procedures dictated by air traffic controllers. Those procedures typically result in a stair-step-style descent to the airport in which a controller instructs the pilots on their heading, speed and altitude and brings them down in a series of altitude changes.
That traditional procedure requires aircraft to descend and then level off several times. Each time the aircraft levels off, the pilots must increase power to maintain altitude.
Under the OPD procedure, the descent is a constant drop that can be accomplished in most cases without increasing engine power above idle until immediately before landing.
In a step-down descent, a flight approaching SeaTac might be asked to level off three times before descending to the runway. Each three-mile segment of level flight uses about an extra 100 pounds of aviation fuel, said Mike Adams, an Alaska Airlines technical captain. That’s about 14 gallons of fuel.
“You can see that when you’re making thousands of landings every year just how that adds up,” Adams said. “It’s very, very costly.”
Following OPD procedures just for approaches to SeaTac that fly over Puget Sound between Vashon Island and the mainland could save the airlines that fly in SeaTac about 175,000 gallons of fuel a month or 2.1 million gallons annually, the airline calculates. Emission reductions are commensurate with the fuel savings, with a reduction of 22,400 metric tons of emissions annually, the amount emitted by 4,100 cars.
The plan still requires more testing because of the complexity of operating in a crowded environment such as the Puget Sound area, Adams said. Once the FAA gives its blessing, the optimized descent plan would be published and available to any airline or aircraft owner who is equipped and trained to use it.
Most airlines have planes equipped with electronics for GPS navigation.
Other airlines such as Southwest, which bought its 737s without the equipment needed for satellite navigation, are rapidly retrofitting the aircraft, Adams said.