A New Technique for Quieter Landings

A New Technique for Quieter Landings  
The Boston Globe, MA

Monday, December 22, 2003  
 
BOSTON Researchers have demonstrated a new way to quiet the thunderous sounds 
of jets approaching airports, offering hope for people who suffer from noise 
under major flight paths.

The team, led by a scientist at the Massachusetts Institute of Technology, has 
designed a new way for planes to land that keeps their engines quieter and 
farther from homes. Termed a "continuous descent approach," the technique calls 
for an approaching plane to stay high for longer than is done now, and then 
glide toward the runway with its engines idling, reducing the noise it 
emanates. In a test of the system in Louisville, Kentucky, the first in the 
United States, the noise on the ground decreased by up to 6 decibels - the 
equivalent of shutting down three of a plane's four engines. "You get a 
significant reduction in noise," said Ralph Dormitzer, who was not involved in 
the research and is co-chairman of a citizens' group that advises Logan Airport 
in Boston on noise issues. "We would like to see this done here."

Before the technique can be widely adopted, the team has to win the Federal 
Aviation Administration's approval and then solve technical issues that 
currently prevent the technique from being used in a heavy-traffic airport.

The technique represents an important new way to help solve a problem that has 
plagued communities and held up the construction of runways, contributing to 
congestion and delays in air travel around the United States. The test showed 
that the new approach can bring large reductions in noise without the need for 
new technology, and that it might even save money and reduce pollution by using 
less fuel. "You get a lot of bang for the buck," said John-Paul Clarke, who is 
leading the research and is an associate professor of aeronautics and 
astronautics at MIT. When an airplane approaches an airport now, air traffic 
controllers typically direct the plane to reduce its altitude in steps, 
descending a bit and then flying level. When the plane is close to the airport, 
it intercepts a radio beam and follows the beam down for the final approach to 
the runway. This means that jets come in low and with their engines running 
loudly. Jets land this way partly to ensure that they will lock onto the 
correct radio beam for their final approach, Clarke said.

The new method makes use of the sophisticated avionics on modern jets, which 
allow planes to pinpoint their position three-dimensionally. Using the flight 
computer, a pilot can direct the plane to the exact point where it is sure to 
pick up the correct radio beam. The plane can then follow the beam in, on a 
slow glide, to the airport.

The new technique would not make any difference to an airport's immediate 
neighbors, Clarke said, since within about 5 miles of the airport there would 
be no difference in altitude. It would make the biggest difference at about 7.5 
to 15 miles, or 12 to 24 kilometers, out.

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