3.2.5.2. PROPULSION SYSTEMS MAINTENANCE
During normal operations all engines will experience rubbing, thermal stress, mechanical stress, dirt accumulation, foreign object ingestion and so on. These effects will eventually result in a measurable decrease in performance. Typical indicators of engine performance are:
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Exhaust Gas Temperature (EGT) increase: as engine efficiency decreases more fuel is required to achieve a given thrust. An increase in fuel required will typically produce an increase in EGT. Monitoring EGT margin (see note 1 below) at take-off is a good indicator of engine deterioration. This can easily be done using data recorded during the flight that is subsequently processed on the ground by engine health monitoring software.
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Specific Fuel Consumption (SFC) also typically increases as engine efficiency falls (again, due to the need for more fuel to achieve a given thrust). This SFC degradation has a direct impact on aircraft performance in terms of Specific Range and thus on the fuel burn for a given mission.
The degradation of these parameters and the consequences for fuel consumption must be balanced against the significant costs that will be incurred when the engine is eventually removed from the aircraft for overhaul. The moment of the engine’s overhaul may be postponed through careful maintenance of the engine while it remains on wing.
When the time to remove the engine arrives, the extent and cost of the overhaul and refurbishment must be carefully balanced against the improvements in EGT margin and fuel consumption it will bring. These aspects should be carefully assessed and regularly reviewed with the engine manufacturer or using the services of one of the many third party engine support companies.
Routine monitoring of engine and aircraft performance using the tool provided by the engine manufacturer and Airbus Aircraft Performance Monitoring software (refer to text box on page 13) will not only allow long-term performance degradation to be assessed but also permit detection of unexpected shifts in engine/aircraft performance. Timely detection will allow appropriate maintenance actions to be launched and minimize any additional fuel consumption associated with the problem.
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