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An overhaul is dictated by one of three factors. The easiest factor to predict is called “life limits on parts.” The Federal Aviation Administration demands that certain critical components be replaced after a given number of flights or flight-hours. About one-third of engine removals are due to this, says Rusty Irving, head of GE’s information technology lab in Niskayuna, NY. Another third occur because the exhaust gas temperature of the engine has risen too high-an indication that parts are wearing out and forcing the engine to run hotter to create the same thrust. The rest of the removals stem from a variety of hardware problems, such as a bird or other foreign object being sucked into the engine, or a leak or crack that exceeds some predefined limit.

The ability to forecast when engines need servicing would allow the company to plan how many spare engines it needs to have on hand at any given time. But in the past, Abernathy says, techniques to predict when an engine would need servicing were little more than blunt tools. The statisticians could figure how soon the typical life limits on parts would force a given engine to be overhauled. They could also calculate how rapidly the exhaust gas temperature increased on average for all the planes in a fleet, which gave a rough indication of how soon an engine might have to come off for that reason. “Then we’d throw in 20 or 30 engines on top of that”-to account for removals due to hardware problems-“and that was our number,” Abernathy explains.

This would work fine if every engine behaved like an average engine. In reality, though, Abernathy says, engine deterioration rates can vary tremendously. The new statistical tools allow GE Engine Services to predict when each individual engine is likely to need an overhaul, then combine those forecasts to create a month-by-month projection of how many engines will be sent in for repair. And, he adds, because the statistical tools also predict why each engine will need servicing, “we can even predict the turn times”-that is, how long each engine will be in the shop. This enables the airline to look a year or more into the future and see how many engines are likely to be “off wing” at any one time. If one month looks to have more than its share, the airline may opt to move up some of the anticipated overhauls to lessen the need for spares and lower the demand on the overhaul center.

Ultimately, improvements and cost reductions in sensors and computing power will enable remote monitoring and diagnosis to move to smaller items, including consumer products. Major carmakers are already working on systems that will spot and report maintenance problems in cars. At GE, the appliance division is developing refrigerators, washers and other machines that can receive instructions and report operating conditions over the Internet, while Whirlpool, Bosch, Samsung, IBM, Cisco Systems, Microsoft and other companies are working on standards and designs for a variety of Internet-enabled appliances.

One idea under consideration is to build appliances capable of making their own service appointments before their owners even recognize something is wrong. If, for instance, an oven uses too much electricity to achieve the desired temperature, it might alert a service center that the heating element is close to breakdown. Engineers say the major hurdle to realizing that scenario is not technical but psychological: getting people used to the idea of a repairman ringing the doorbell and announcing, “The oven asked me to come.”

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