Downloaded from https://www.everyspec.com ADS-79D-HDBK G.7.3.5 Torque. Torque is a measure of the mechanical power output from the engine and should be measured as defined in the engine design specification for the duration of engine operation at an update rate of at least 1Hz. Ideally, each life-limited part should be monitored separately by the EMS/EHMS. A widely used method is to monitor only one or two parts on each rotating shaft and to derive the life usage on the unmonitored parts by applying relational ‗read-across‘ factors.
This method is practical only when the life usage relationship between parts is linear and is usually more feasible when thermal stresses are absent or negligible. G.7.3.6 Lifing Algorithms. Lifing algorithms are used to compute in real time the damage accrued and the remaining useful life of components. These algorithms are developed from the more detailed analyses used during the design process to calculate the component lives. They are frequently referred to as reduced order models (ROM) or Life Usage Indicators. If more than one critical failure can be present, enough features should be monitored to ensure the integrity of the modeling process.
The engine life model should take into account the engine operating conditions and the mechanical properties of the materials and components. The EMS/EHMS, therefore, should track the operating conditions and provide data to assess engine status to the module level while providing sufficient information to determine required maintenance actions. The EMS/EHMS should have extensive built-in test (BIT) capability to ensure that internal computational routines are operating within their defined limits. In the event of an EMS/EHMS failure, the affected module or card should be identified and the effect of the failure on recorded data should be considered.
In addition, any cycles incurred but not recorded should be input manually either in accordance with a simplified algorithm or a worst case scenario to ensure that components have not consumed more life than is recorded. The procedures which control the manual activities and any techniques used to identify questionable data and to repair it or compensate for it should be subject to audit to provide assurance that they are adequate and satisfactorily maintained. 40 The audit should account for and include the following aspects: a. Identification of personnel carrying out the download under various circumstances b. Storage capacity of the airborne unit and transfer unit c.
The required frequency of downloads and the number of aircraft and flight which can be downloaded to the transfer unit without return to the ground station d. The identification of and compensation for system failures and data loss e. Program for regular critical reviews of the system outputs f. Training program for operating personnel 40 RTO TR 28, ―Recommended Practices for Monitoring Gas Turbine Engine Life Consumption‖, North Atlantic Treaty Organization, Research and Technology Organization, April 2000, pg. 7-13. 129