Air Transport World

Raising the MRO IQ: as engines become smarter, condition monitoring evolves toward reliability analysis.(MAINTENANCE)

ENGINE CONDITION MONITORING is moving from diagnostics toward prognostics, pushing at least part way toward true condition-based maintenance. Sensors and systems have become very good at forecasting and thus preventing potential failures, saving money on delays and major repairs. But they cannot reliably predict success: How much longer a part or engine can stay on-wing.

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Engines incur very large expenditures during off-wing overhauls, which happen for one three reasons. First, inspection can detect major damage to parts. Engine monitoring can trigger inspections and may prevent major damage. Second, performance can deteriorate. Monitoring continues to improve in tracking and predicting, and sometimes helping to prevent, deterioration, especially of exhaust gas temperature margins. The third reason is that conservatively calculated terms of life-limited parts are reached. Extending the term of LLPs to reflect actual usage more realistically is the next big and very difficult challenge that engine designers and monitors face.

Smarter maintenance will be possible as new airframes and engines are delivered in the next few years and better methods for getting data to the ground and interpreting it are developed. But progress in predicting part life will come only in the middle of the next decade as engines now on the drawing boards come into service.

Much progress already has been made. "On older engines there were maybe 20 variables available," notes Kim Smith, a technical specialist with Delta TechOps. "On the 777 there are over a hundred."

Rick Donaldson, manager-diagnostic and prognostics centers at GE Engine Services, says GE is working to expand sensor coverage further on future engines to monitor LRUs and detect mechanical problems with bearings, gears and airfoils. …

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