Sofema Aviation Services (www.sassofia.com) takes a brief look at ECM & Cruise Trend Analysis
Introduction
The concept behind Engine Condition Monitoring is based on the analysis of real-time data to enable analysis and to be able to draw conclusions regarding the health of the engine.
It is understood that most failures do not occur instantaneously, but rather through a gradual deterioration, which is a process that can be monitored.
ECM and Cruise Trend Analysis Considerations
To monitor the performance of an engine it is necessary to be able to interpret data that can be representative of the engine’s health. For data to be considered valid for trend analysis it needs to respect a set of conditions which makes it eligible to be considered a Stability Point for a given flight.
During normal operation all engines will experience rubbing, thermal stress, mechanical stress, dirt accumulation, foreign object ingestion and other events which will eventually result in a measurable decrease in efficiency.
By continuously monitoring the evolution of key parameters, deterioration in engine performance can be detected as well as early signs of engine faults and thus appropriate measures can be undertaken.
Parameter trend monitoring is compared to a baseline model that represents the expected behaviour of a given engine, taking into account ambient and thrust conditions, as if it was newly installed or at its best performance.
The deterioration over time between measured data and the baseline model is known as “Delta” parameter.
Monitoring the evolution of deltas provides information regarding the current state of an engine and provides for an estimation of how its performance has deteriorated Over a given series of flight cycles.
These parameters are considered to be the performance indicators, also known as engine Performance Parameters.
The EGT, FF, N1 and N2 are plotted as a function of the EPR and for different Mach Numbers.
Today’s ECM tools automatically record data from the engines and perform trend analysis, making this information available to the operators.
Parameter Corrections
The measured engine parameters values vary not only with the power condition but also with ambient conditions at the engine’s inlet
A change in the inlet temperature and/or pressure is coupled with a change in the gas path parameter’s values, which makes it difficult to establish a common ground for the thermodynamic relationships between gas turbine parameters unless ambient conditions are accounted for. (This issue is solved by correcting the engine parameters.)
Engine Bleed Considerations
Highly pressurized air is extracted from the engine to feed the aircraft’s pneumatic systems that drive the air conditioning systems, wing anti-ice, amongst others. This can have major effects on the performance of an engine and needs to be taken into account. The air is normally bled from the intermediate stages of the High Pressure compressor.
Sofema Aviation Services offers EASA Compliant Regulatory and Vocational Training including Engine Condition Trend Monitoring. For details please see www.sassofia.com or email office@sassofia.com
