From 65 miles away, air traffic controllers detected small bits of engine debris falling from Southwest Airlines Flight 1380 on Tuesday using a tried-and-true technology: radar.

These beams of electromagnetic energy are used to track thousands of airplanes every day, enabling air traffic controllers to pinpoint each aircraft's location by measuring how long it takes the radar to be reflected off a plane's metal surface back to an antenna.

But at the frequency used in standard air traffic radar — about 3 gigahertz — the system can pick up objects as small as one inch across, according to Christopher Peters, a Drexel University professor of electrical and computer engineering.

Within moments of the engine failure on Southwest Flight 1380 on Tuesday, air traffic controllers started tracking the debris so that it could be retrieved and analyzed to determine what went wrong.

Meteorologists immediately determined the wind speed in that location, allowing for a rough estimate of where the debris might land, said Robert Sumwalt, chairman of the National Transportation Safety Board, in a briefing Wednesday.

"And sure enough, the debris landed in about the area that they anticipated it would be," Sumwalt said.

So far investigators have recovered pieces of cowling, the metal skin surrounding the doomed jet engine. They still are seeking the outer section of a fan blade that broke off due to a phenomenon called metal fatigue and have asked residents in the area of Bernville, Berks County, to keep a lookout.

Radar at frequencies higher than the 3 gigahertz used by air traffic controllers can detect objects even smaller than one inch across, provided they are made of a reflective material such as metal, Drexel's Peters said. And if they are powerful enough, radar beams can be used to detect debris in space, as Lockheed Martin engineers have done at a Moorestown test facility, at the behest of the U.S. Air Force.