Technology: Stethoscope for Jet Engines

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From the earliest days of aviation, when the whistle of wind in guy wires gave the trained pilot as much information as any instrument, airmen have relied on their ears to recognize the sounds of trouble. Now the roar and whine of modern jets make it hard for the human ear to detect anything but the most obvious trouble. And by then it may be too late. To give pilots and maintenance a boost. General Electric is developing a sonic analyzer that can be applied to jet engines much as a physician's stethoscope is applied to the human chest. A trained and sensitive electronic ear, it listens for malfunctions and locates trouble spots.

What the analyzer does is to compare an engine's sounds with what those sounds ought to be. The taped sounds are fed to a computer, which translates their complex wave shapes into the language of binary numbers and then works out a program for the analyzer. The analyzer has been "taught" to read that language and recognize normal and abnormal noises in the functioning of specific engine parts. All a mechanic has to do is hold the analyzer's microphone near a roaring engine. In seconds, the little apparatus will flash a light indicating "no failure" or if there is trouble, signal its location.

For its prototype, G.E. recorded and encoded the sounds of normal engines in U.S. Navy Phantom and Vigilante aircraft along with 62 separate malfunctions. A portable version of the analyzer, which should be in use by next year, could easily be adapted for work on automobile engines on industrial assembly lines.