Downloaded from https://www.everyspec.com ADS-79D-HDBK EMS/EHMS power assurance checks. For EMS/EHMS power assurance checks employing an adaptive line to predict power available, flight test plans should demonstrate accuracy requirements using a minimum of 6 flight test engines calibrated in a test cell either before or after ―sufficient‖ flight testing with the EMS/EHMS algorithms on the airframe. ―Sufficient‖ is defined here as enough flight test data such that the engine Shaft Horse Power versus Turbine Gas Temperature characteristic has adapted to reflect an engine-specific profile.
Two of the six flight test engines should be degraded at or below what is currently defined as field acceptable. The engine calibrations should consist of a minimum of 10 data points and should include all engine rating points to include Contingency rating and nominal Maximum (10 minute) limiting temperature rating if possible. The Government should approve the engine calibration plan prior to data collection. G.7.4.2 Engine Stall Monitoring. The propulsion system should be able to identify engine stall events, categorize the severity of the stalls, and indicate appropriate maintenance actions. G.7.4.3 Anomalies and Fault Detection.
Fault Detection for CBM concerns the use of sensors and various signal processing algorithms to identify and isolate a fault in a part or subsystem of the engine. The number of faults detected through sensing is determined by FMECA, which is accomplished as part of engine acquisition. The FMECA defines the expected failure modes and faults that the engine may experience. The EMS and EHMS should be capable of detecting all flight critical faults through data collected by installed sensors. The EMS should also be able to detect at least 70% of all faults and failure modes, which result in the need for maintenance action, established by FMECA accepted by the Government Program Manager.
When the EMS/EMHS detects a fault and directs maintenance action to correct the fault, there should be no more than 10% false positive indications based on subsequent tear down analysis. The sensors and data management hardware and software should be able to develop CIs and HIs that correspond to flight critical faults with sufficient time to prevent catastrophic failure and possible injury to the flight crew. In some cases, such as LCF, detection of the faults is not possible in a meaningful time frame prior to catastrophic failure.
In those cases, the FMECA should document those failure modes and indicate mitigation methods to preclude their occurrence with means other than direct monitoring. When the sensors and data management equipment detects an abnormal, but unknown condition (an anomaly), it should record the raw signal in a sufficient interval surrounding the time of occurrence, as well as the computed CI during that interval for post flight processing and analysis.
Determining the sensor strategy, sensor placement, Condition Indicator (CI), and Health Indicator (HI) development for the engine is accomplished the same way as for other aircraft systems and components because of the central role the engine plays in aircraft performance. It is natural to allocate more sensors, computing resources and testing to ensure that engine fault detection is a robust part of the aircraft CBM system. G.7.4.3.1 Engine Component Faults. EMS and EMHS should be able to detect all flight critical engine faults with 90% confidence. G.7.4.3.2 Instrument Faults.
EMS and EMHS should be able to detect and isolate sensor and instrument faults in their system and highlight suspect data caused by sensor or instrument error. 133