Downloaded from https://www.everyspec.com ADS-79D-HDBK This appendix will further define these functions and the minimal requirements for an EHMS on turboshaft engines and APUs. G.6 GENERAL GUIDANCE Turbine engine monitoring technology has progressed significantly over the past four decades as illustrated in Figure G-4. Engines first started incorporating exceedance monitoring of parameters such as exhaust gas, over-temperatures, and turbine over-speeds to prevent accelerated accumulation of damage and to serve as guides for maintenance action. Because the exceedances were normally displayed on cockpit gauges, this put the burden on the pilot to note and record the incidents.
To reduce pilot workload and improve reporting, systems were developed to automatically record the exceedances. From there, systems progressed to collecting data in windows of time around the exceedances and then to algorithm/signal processing to look for faults (mostly in vibration and temperature). At about the same time, engine manufacturers began to develop relationships of time, temperatures, and cycling to calculate ―life usage indicators‖ (LUIs) to replace the use of simple operating hours for life calculations. These limits (either hours or LUIs) were justified by analysis, testing, and evaluation of teardown results.
Debris analysis in engine oil, to detect unexpected wear in internal components, began in the 1970s with off-aircraft spectral analysis. In the late 1990s and early 2000s the systems became laser powered to measure the size and distribution of particles in the oil. From that finding, particle distribution and failure analysis may be conducted. The methodologies used for turbine engine health management can be grouped in two broad, complementary areas: life usage monitoring for life-limited components and condition monitoring for ―on condition‖ maintenance.
In general, life usage monitoring is concerned with tracking the changes in the engine‘s operating conditions during the mission because these cyclical changes induce stress and thermal fatigue in engine components. With condition monitoring, the emphasis is on checking the engine‘s behavior during operating conditions and comparing it to a baseline. Engine behavior that differs from the baseline can be indicative of normal degradation or an anomaly that is a precursor to failure. The following subsections provide a general discussion of these two areas as well as lubrication, fuel, and APU monitoring.
117 TABLE G-I EHMS Main Functions usage monitoring exceedance recording remaining useful life estimation performance trending power assurance checks fault detection and diagnosis time to failure prognosis