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Commercial jets are at their noisiest and dirtiest when they're coming in for a landing. As they descend, they rattle homes, damage ears, increase blood pressure and, of course, spew loads of pollution. Eager to clean up their act and keep the neighbors happy, many airports are adopting a cleaner, quieter way of landing aircraft.
The continuous descent approach has been shown to cut noise, conserve fuel and reduce emissions -- all without requiring new technology or spending hundreds of millions of dollars- which is why airports like LAX are beginning to experiment with it.
Aircraft typically land using what is known as the stepped approach. A pilot reduces thrust and the plane starts to descend, then the pilot increases thrust to level off, repeating the cycle until the plane is on the ground. It's standard practice at most airports, but it's far from perfect. Constant acceleration and deceleration of the engines not only burns loads of fuel, it creates a lot of noise, which is a big headache for people living near airports.
With a continuous decent approach, a pilot lines up with the runway much earlier -- sometimes up to 40 miles away -- cuts the thrust once and descends at a consistent rate. If the stepped landing is a flight of stairs, then the continuous descent approach is a wheelchair ramp. And since the planes aren't constantly ramping up and pulling back on the engines, it's a lot more efficient.
So why aren't all the airports doing it?
The lack of available airspace has prevented continuous descent from being more widely adopted. A long, smooth landing approach requires lots of space, and anyone who flies these days knows that space above airports is at a premium.
But where it is being used, the results are encouraging. UPS pioneered the approach and found nitrogen oxide emissions dropped by 34 percent below 3,000 feet and engine noise fell by 30 percent within 15 miles of the airport. The planes also saved 250 to 465 pounds of fuel per flight.
By some estimates, an Airbus A330 using continuous descent will save up to 450 pounds of fuel and reduce CO2 emissions by nearly 1,000 pounds. It may not be as high profile as experimenting with jet fuel made from pond scum or designing a quieter, more fuel-efficient jet engine, but multiply 450 pounds of fuel by the thousands of planes that land every day and continuous descent approach could make a real difference.
Airports in Scandinavia have taken the lead on continuous descent, with the Stockholm airport allowing all airlines to use the procedure and planning to increase continuous descent landings to 30 a day. Airports in Gothenburg, Umea, and Malmo will begin using the approach within the next three years, albeit during off-peak times when airspace is at less of a premium.
*Photo by *Flickr user lillith121.
