Downloaded from https://www.everyspec.com ADS-79D-HDBK a. Data acquisition b. Data reduction c. Data presentation d. Interpretation of results Condition monitoring relies on techniques such as trend analysis and anomaly detection. For trending analyses, parameters that have large errors inherent in their measurement systems should not be used as a basis for comparison with other more consistent parameters. Furthermore, parameter data should be acquired at stable conditions (steady state) which will allow shifts in parameter behavior to be more readily detected.
Transients caused by changes in accessory settings or control settings can add noise or variation to the parameter trends making the detection of a true shift difficult. If data smoothing algorithms are used to improve the readability of trend data, they should not mask the presence of a true parameter shift. G.7.4.1 Performance Monitoring. Aircraft engine reliability has steadily advanced through the history of Army aviation. Removing the engine for failure to perform in accordance with design limits, typically associated with torque, temperature, or vibration, is now more common than removal for catastrophic failure.
Performance monitoring is, therefore, the first ‗level‘ or type of condition monitoring. Engine Monitoring Systems should include the means to periodically assess engine parameters in comparison to those same parameters as measured upon engine installation in the airframe. This periodic assessment should be done in similar states of power and load for consistent comparison, and should be defined by the Using Service with input from the engine OEM. The comparison of these parameters through basic trend analysis, or other algorithms, should also be defined by the Using Service with input from the OEM.
The OEM should determine what elements of performance monitoring should be included in flight and propose those elements to the Using Service aircraft program management office as part of the Condition Based Maintenance Plan for the engine. When parameters are selected for off-board monitoring, the means and validation of this off-board monitoring should also be included in the CBM Plan for the engine and validation of the monitoring should be part of the overall engine test and evaluation process. G.7.4.1.1 Power Assurance Monitoring. Power Assurance Monitoring is a special case of performance monitoring.
Historically, flight crews have conducted power assurance checks as part of pre-flight planning and mission preparation, as well as during post maintenance functional check flights. Power Assurance checks are performed to validate the expected level of torque supplied by the engine at given environmental conditions of density altitude and temperature under operational conditions. These checks are typically performed to ensure that the engines are capable of supplying sufficient torque to complete the anticipated mission.
Engines equipped with EMS or EHMS capable of performing power assurance checks should automatically assess the engines for power assurance check on the first application of power to hover the aircraft, and should display a simple cockpit indication (e.g., ‗green light‘ for acceptable power / percent power available) to the flight crew. Since this information to the pilots is critical safety information, Automatic Power Assurance Algorithms should be baselined and checked against calibrated engines. The following detailed topics should be considerations in implementing Power Assurance systems in EMS/EHMS: G.7.4.1.2 Safety Assessment.
A safety assessment should be conducted in accordance with (IAW) SAE ARP 4761 and initiate a Functional Hazard Assessment (FHA) to identify and classify failure condition(s) associated with the system functions and combinations of functions. SAE ARP 131