Jet engine icing research tackles dangerous flight problem

Credit: NASA

Technicians install water sprayers in the jet engine icing test chamber at Cleveland's NASA Glenn Research Center. The sprayers will produce tiny ice crystals that can clog or damage engines.

On a stormy July evening in 2004, more than five miles above the South China Sea, the engines powering a large passenger jet en route to Taiwan suddenly failed.

A simultaneous engine shutdown on a large, modern aircraft is almost unheard of.

After a harrowing 75 seconds, the pilots managed to restart them, and the jet landed at the Taipei airport without further problems. But the incident set off alarms in the aviation community.

Minutes before its engines quit, the jet had been skirting thunderstorms spawned by a distant typhoon.

Investigators first thought the storms' powerful updrafts had pulled rain high into the atmosphere, temporarily smothering the engines when they sucked in gouts of water instead of air.

The jet's pilots had seen and heard droplets hitting the windshield, bolstering the rain theory but the jet's radar sweeps were clear, with no echoes from rain and the temperature at the altitude where the trouble began was a frigid minus-44 degrees, far too cold for liquid water.

Researchers eventually concluded the engines must have been choked by tiny ice crystals as small as flour grains, a dangerous, unexpected phenomenon that aviation officials urgently want to learn more about so they can lessen its risk.

Much of that work will take place at Cleveland's NASA Glenn Research Center, where engineers are readying a unique test chamber capable of mimicking the odd weather conditions that threatened the Taipei-bound jet, and have caused more than 150 other in-flight incidents.

"These things are happening pretty frequently, like one incident every month or so," said Glenn project manager Ron Colantonio. "NASA is working with the aviation community to understand what's causing the problem and how to mitigate it."

Glenn officials recently unveiled the silvery, boxcar-sized engine icing tunnel during a visit by NASA administrator Charles Bolden.

Glenn engineers previously had used the tunnel for other types of jet engine tests. With $15 million in Recovery Act and NASA money, they've retrofitted it with water sprayers that will produce the minute ice crystals believed to be causing the engine problems.

Sensors will track the performance of jet engines mounted on a frame in the icy air stream.

Aviation safety experts have long recognized the danger from ice buildup on wings and other external aircraft surfaces.

The hazard is caused by super-cooled liquid water freezing on contact, disrupting smooth airflow and hampering lift.

For decades engineers in Glenn's Icing Branch have led international efforts to develop better ice forecasting methods, icing sensors, anti-icing aircraft designs, and improved pilot training.

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