"We are now preparing for our descent. Please make sure seatbacks and tray tables are in their upright and locked position..."
These words precede the long, nerve-racking and environmentally damaging process of taking a plane from a cruising altitude of nearly 35,000 feet to docking at an airport. Seattle-Tacoma International Airport (Sea-Tac) is battling this inefficient process through the implementation of programs that will save passengers time, airlines fuel and the environment from harmful emissions.
According to the most recent emissions report by Sea-Tac from 2006, aircraft and ground activity in the area surrounding the airport produced approximately 641,000 metric tons of carbon dioxide per year. That’s equivalent to the weight of 4,000 Boeing 747s.
Sea-Tac is working on several environmentally-conscious projects, including continuous descent approach and pre-conditioned air.
"We see a competitive advantage of being the cleanest, greenest most energy efficient port in the nation," said Steve Rybolt, environmental management specialist for Sea-Tac.
Do you remember a descent that left your stomach upset or made your head spin?
The plane lurches as it falls from 14,000 to 10,000 feet. As it drops abruptly, so do the passengers’ stomachs. Some people are nervous; others are nauseous or lightheaded. Hands clutch armrests, magazines or books to relieve the tension of descent.
This experience will hopefully be a thing of the past with the adoption of continuous descent.
The Federal Aviation Administration, Alaska Airlines, Horizon Air, Southwest Airlines, Delta Air Lines and Sea-Tac are working together to begin using continuous descent, a new landing approach. The standard descent process relies on a tiered approach where planes are brought down in steps, resulting in a descent path resembling a flight of stairs. Each time the plane drops a step, the pilot must decelerate and then accelerate to maintain speed, which burns through fuel quickly.
Continuous descent brings planes to the runway on a smooth slope, thus saving the pilot from increasing and decreasing the throttle until they touch the ground. Each landing with this approach saves 300 to 600 pounds of fuel, said John-Paul Clarke, associate professor in the school of aerospace at Georgia Tech University.
If every one of the 170,000 landings at Sea-Tac each year used the continuous descent approach, it could prevent almost 54,000 metric tons of carbon dioxide from entering the air, which is equivalent to the emissions created by nearly 11,300 cars per year.
Clarke, who has worked on the continuous descent landing since 1993, said the approach has been tested with many models of passenger aircraft and it not only decreases fuel burn, it also cuts flight time by 2 1/2 minutes and noise by up to six decibels.
To use this landing method, a pilot looks for minimal air traffic, a defined path from the top of the descent and no further directions from air traffic control, said Sarah Dalton, Director of Airspace and Technology for Alaska Airlines.
Planes using this method have to be spaced out further away from the airport than with the current system because the descent process starts nearly 150 miles away from the destination.
Currently, there are points along an airplane’s descent that must be hit at specific altitudes, causing pilots to make more adjustments using the throttle, Dalton said.
Knowing where your plane is in relation to others is vital to successful continuous descent landings. The idea is to have a clear path, allowing pilots to adjust the plane as little as possible, Dalton said. This requires spacing technology that integrates your plane with the others around it.
A difficulty in switching all descents to this procedure is that new instrumentation would have to be installed on the ground and in many of the aircrafts, Rybolt said. This problem is being dealt with in older planes, and newer models of planes will come equipped with the necessary technology to use continuous descent.
Alaska is one of the airlines using basic forms of continuous descent. However, they will not reap major rewards until more advanced systems and technologies are in place to deal with these barriers, Dalton said.
The only three airports in the U.S. using this landing procedure on a regular basis are Los Angeles, San Diego and Louisville, but Seattle hopes to join this group by early 2010. Continuous descent approach will likely be the standard descent process in 10 years, Clarke said.
The reduction of fuel burn and emissions is not only a priority while an airplane is in flight, it’s also important while it is on the ground.
Imagine you’re sitting in a window seat as other passengers continue to board a plane bound for Hawaii. A look out the window reveals a flurry of activity. The runway below is littered with several large carts, thick tubes and heavy machinery. As you reach up to turn on the air above, you wonder what all the equipment outside is used for. The cool air blows toward you, instantly relieving the stuffiness of the cabin. Next stop, Hawaii.
Air-conditioning is a necessity on planes in order to keep the cabin at a comfortable temperature, Rybolt said.
Many airports are making efforts to improve air quality through the use of pre-conditioned air, and Sea-Tac is ready to take the technology to the next step.
Whether in the air or on the ground, an airplane constantly runs air-conditioning. When an aircraft is in flight, its engines create the cool air, but on the ground, the auxiliary power unit aboard the plane takes over the task. Running the power unit wastes fuel and spews greenhouse gases such as nitrous oxide and carbon dioxide into the atmosphere.
Airports offer diesel or electric ground pre-conditioned air units – this equipment is what you saw while waiting for your flight to Hawaii to take off. The units look like giant stand-alone freezers on wheels. They connect to planes through a yellow tube resembling a covered slinky. A thick electrical cord connected to the gate is also plugged into the plane so cabin lights and cockpit instruments can function. The combination of these two services allows the aircraft’s engines to be turned off.
Sea-Tac is planning to build a centralized pre-conditioned air system that will significantly reduce emissions and fuel consumption, said Russ Simonson, a senior environmental program manager at Sea-Tac.
The centralized system will be housed within the main terminal and works the opposite of the boiler. Air flows over a chiller, which is essentially a large block of ice, and is then pumped through ducts to each gate. At the gate, the air travels through a tube leading from the gate directly into the plane.
Over a year, the new system could reduce carbon dioxide emissions by 69,000 metric tons, according to Sea-Tac studies.
"Imagine taking 13,000 cars off the road a year–that’s the equivalent of us putting in a centralized pre-conditioned air system," Rybolt said.
Simonson said the $30 million project has been in development for the last seven years but didn’t gain broad airline support until the fuel prices increased and the environmental benefits had been fully explored.
The reduction in fuel is good for the environment and the airlines’ pocketbooks, which will hopefully save travelers money, Rybolt said.
If everything runs smoothly, the centralized unit should be functional in early 2011.
While continuous descent approach helps reduce plane emissions during flight, pre-conditioned air will help planes conserve fuel while they stay idled at the gate. Airports are making the effort to reduce their carbon footprint, and procedures like these will only make this next step more feasible.
Harte Onewein studies journalism and public relations. He has been published in the Western Front and the Whatcom Community College Horizon.