What is Engine Condition Monitoring (ECM)?

ECM is the process of the monitoring of key engine parameter to detect impending failures and assess engine performance.

ECM essentially uses standard engine and aircraft instrumentation to support the monitoring of the various parameters. As such no additional measurement equipment is needed.

How does it work?

So the process of Engine Condition Trend Monitoring (ECTM) monitors and measures the changes in any of a number of performance parameters of the engine.

The process of analysis allows for the monitoring of the engine performance deterioration and provides a “heads up” regarding the potential impending malfunction of certain engine components and accessories.

The various technical requirements of the ECTM for a given engine type are specified by the engine manufacturer.

What are the Operational & Financial Benefits of the utilisation of ECM / ECTM

Minimises the possibility of unscheduled downtime whilst being able to avoid secondary damages and AOG’s

Supports early line maintenance decisions and permits better engine removal planning

Increased fuel efficiency and overall fuel consumption thanks optimized core engine cleaning

Provides for optimum aircraft operational planning as well as optimized spare engine management

 Continuing Airworthiness Requirements & Benefit of ECTM

Early detection of engine deterioration is of critical importance to schedule timely maintenance action, and ECTM has been widely used to facilitate this.

ECTM is considered to be part of a good engine maintenance program and is mandatory in the following instances.

Turbine engine powered aircraft where the flight manual permits reduced power take off’s, the flight manual will contain a mandatory requirement to have procedures to ensure that the engine will make the rated power.

Incorporation of ECTM into the engine maintenance program, along with the specification of some engine parameter limits to ensure rated power, is one of the methods to meet this requirement.

In circumstances where the ECTM is not carried out in real-time, it may be necessary to supplement ECTM with full rated engine runs at regular intervals to meet the flight manual requirements.

Considering ECTM System Process Elements

ECTM relies on consistent and reliable engine performance data that includes altitude, outside air temperature (OAT), aircraft speed, turbine gas temperature, engine rpm, propeller rpm, power developed, fuel flow and others.

Effective implementation and integration of ECTM into the engine maintenance program requires the following sub-systems:

Data acquisition

Data entry

Data analysis

Follow-up actions

Computer hardware and software

Large transport aircraft manufactured by Boeing and Airbus typically have highly integrated real time data acquisition and analysis systems to support ECTM

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.

Aircraft engines are high value very complex system, requiring adequate monitoring to ensure flight safety and timely maintenance.

Cockpit displays present engine performance information the provision of information such as rotational speeds, engine pressure ratios, exhaust gas temperature.

Oil supply to critical parts, such as bearings and gears is vital for safe operation so early warning regarding deterioration is essential. (For monitoring fuel and oil status, indicators for quantity, pressure, and temperature are used.)

In addition to mentioned crucial parameters, vibration is constantly monitored during engine operation to detect any possible unbalance at the earliest opportunity.

Essentially any of the above parameters can provide as an early indication and to mitigate costly component damage and/or catastrophic failure.

To accomplish the monitoring task in the most effective way requires the support of automated software systems.

Engine Monitoring Systems (EMS) have become increasingly standard as the computational ability of the industry advances through technological changes

 Parameters for Engine Monitoring Systems

The typical parameters that are recommended for monitoring in aircraft are as follows:-

Temperatures (inlet, outside air, exhaust gas, compressor, turbine, bleed air),

Pressures (inlet, compressor, discharge, lube oil, bleed air),

Oil System (quantity, filters, consumption, debris, contamination),

Vibration (rotors, shafts, afterburners, reduction gears, bearings, transmissions, and accessories),

Life Usage (operating hours, start times, fatigue, stresses, cracks)

Plus

Additional Parameters – speeds, fuel flow, throttle position, nozzle position, and stator position.

For commercial aircraft, the main parameters that are monitored to determine engine performance are:

Aerodynamic Performance:

EPR (engine pressure ratio),

F/F (fuel flow),

RPM (speed),

EGT (exhaust gas temperature), and,

Throttle Position; (Throttle Lever Angle – TLA)

Mechanical Performance:

Vibration amplitude and oil consumption.

Data Collection

The current practice for commercial aircraft requires the accumulation of continuous monitoring of performance parameters, and recording together with transmission or download to the ground at a certain point.

Cockpit instrument readings may also be taken once a day, or on every flight during cruise conditions. (Company Operating Procedures)

Recorded data is processed and compared to “normal” data established by the manufacturer or operator.

Engine manufacturers typically provide support for on-board diagnosis for Maintenance Purposes.

Condition Monitoring and Diagnosis

Certain kinds of pre-emptive engine failures will result in specific changes in the parameters being monitored providing an opportunity to take early preventative action.

The standard means of monitoring parameters involves the comparison of parameters to reference different levels or by evaluating data shifts through time by trending.

Exceedance monitoring involves the storage of a record of data whenever an engine operating limit (e.g., speed, temperature) is exceeded.

Operating limits for such parameters are typically set by engine manufacturers based on design performance models, and by operators based on field experience from other airplanes and engines

Automatic troubleshooting procedures or expert system diagnostics are used when rules can be defined adequately, to identify the most probable cause of the exceedance and estimate the possible damage.

Commercial software packages have been developed in conjunction with the engine manufacturers to accomplish the exceedance detection and diagnosis task, once the exceedance data has been transferred to the ground station.

Such automation of the diagnosis step using the exceedance and trend data relies on building trend and baseline signature databases through engine manufacturer’s data and through field experience.