Fourth DTSO International Conference on Health and Usage Monitoring The validation of HUMS engine data Joanna Kappas Air Vehicles Division, Platforms Sciences Laboratory, Defence Science and Technology Organisation, PO Box 4331, Melbourne, Victoria, 3001, Australia Summary: Engine Monitoring System (EMS) data is that part of Health and Usage Monitoring System (HUMS) data which relates only to engine management. EMS data from a military aircraft were validated against results from ground running and flight trial tests, conducted by the Royal Australian Air Force. The EMS engine data were validated by comparison against data obtained during the tests from the on-board aircraft cockpit display and Flight Data Recorder and the added-on Digital Bus Analyser (DBA). The engine usage data, including cycles and operating times, were correctly calculated by the EMS during the trials. The total usage numbers though were inaccurately recorded and action has been in place by the RAAF to solve this. The EMS condition monitoring data, consisting of engine data used for performance trending and engine condition snapshot data, were accurately recorded by the EMS. This allows the EMS to be used to implement both on-condition maintenance of the engines and engine component life tracking. Keywords: certification, validation, engine, usage monitoring, condition monitoring, flight trial Introduction The Engine Monitoring System (EMS) is a subsystem within a Health and Usage Monitoring System (HUMS) employed to monitor the four engines of a military transport aircraft used by the Royal Australian Air Force (RAAF). The aircraft was certified for civil use only, conducted by the US Federal Aviation Administration (FAA), and an in-country program was undertaken to extend certification for military operations in an Australian environment. The EMS performs two functions that are important, the engine system life tracking and the engine condition monitoring. The Engine Structural Integrity Program (ENSIP) in the US Military Standards [1] requires recording of the engine operational usage. The RAAF Director General Technical Airworthiness requested that the usage monitoring function of the EMS be validated in order to have confidence in the future use of the EMS to track component lives. This was undertaken for the main engine usage parameters of interest, the engine cycles and engine operating times, and also for the rest of the EMS usage data. The engines are subject to on-condition maintenance, a process that requires repetitive inspections, such as validated monitoring possibly with a HUMS, to determine the condition of components with regard to continued serviceability and corrective action is taken only when required by item condition [2]. The validation of the EMS condition monitoring data was performed to satisfy the on-condition maintenance requirements. The EMS can be described as consisting of three parts (Fig. 1), the processor Nacelle Interface Unit (NIU), the Removable Memory Module (RMM) and the ground-based computer Ground Maintenance Station (GMS). The validation process evaluated the data that is stored in the RMM, prior to reaching the GMS. For a fully functional GMS, GMS output data should re- Eleventh Australian International Aerospace Congress Sunday 13 Thursday 17 March 2005 Melbourne, Victoria, Australia Fourth DTSO International Conference on Health and Usage Monitoring
flect the input RMM data. Because the GMS has currently not been cleared as adequate to correctly report all the information downloaded from the airborne part of the EMS system the validation did not include the GMS data, but concentrated on the airborne data. ENGINE MONITORING SYSTEM NACELLE INTERFACE UNIT REMOVABLE MEMORY MODULE GROUND MAINTENANCE STATION Fig. 1: Engine Monitoring System configuration Validation Process The EMS data were validated, by demonstrating that the engine state was accurately represented both during ground running and flight. This was achieved by a number of tests that provided a baseline of engine data to compare the EMS data with. The activities that were undertaken leading to the validation of the EMS data, included preparing an aircraft test plan, certifying equipment used in the trials, conducting ground runs and flight trial tests, processing the EMS data and the data obtained from other onboard data sources and finally analysing the results (Fig. 2). The tests ensured that sufficient data were gathered for the validation exercise (Fig. 3). The ground running trials, which gathered data from two aircraft over two days, included a number of engine shutdowns and re-starts as part of the EMS usage data validation. During the flight trial, engine performance data were successfully recorded. During both the ground running and the flight trials, the aircrew recorded EMS engine condition snapshots by pressing the cockpit button at specific engine power ratings according to the test plan. The trials were conducted in a well-controlled environment and the video recordings confirmed that the test plan was strictly followed. The engine data that were obtained by on-board sources, to be used for the validation of the EMS data, during the ground runs and flight trial comprised: 1. Video images of the cockpit colour multi-functional display units. 2. Data Bus Analyser (DBA) data. 3. Flight Data Recorder (FDR) data (Fig. 4). A digital video camera was used to record the cockpit display screens during the trials and still images were produced, by post-flight processing, for the times of interest. The DBA, which was approved by the RAAF, prior to the trials, for in-flight use, provided continuous recordings at a high sampling rate. The assumption was made that all data acquisition equipment used in the trials to validate the EMS data, were correctly recording the engine state. A second assumption was made that the
clocks for the aircraft on-board equipment, the cockpit display, the FDR and the EMS were synchronised. The clock of the added-on equipment, the DBA, was manually adjusted to the cockpit time. Aircraft availability and logistics Certification of test equipment Determine test parameters Prepare Test Plan Conduct trials Process EMS and other test data Validate engine data Fig. 2: Flow of activities 1. Ground Runs 2. Flight Trial Engine Usage Data Engine Performance Data Engine Condition (snapshot) Data Fig. 3: Tests conducted to obtain Engine Monitoring System data Cockpit Images EMS Engine Condition Data compared with Data Bus Analyser Data Flight Data Recorder Data EMS Engine Usage Data compared with Manual Test Plan Data Data Bus Analyser Data Fig. 4: Sources of data used to validate the Engine Monitoring System data
The complexity of processing the data was increased by: Different sampling rates for each data source. Different time stamping by the EMS processors for each of the four engines. The EMS performance data are values averaged over a period of 5-10 seconds, depending on whether the data is from the take-off or the cruise record. The data obtained by the DBA and the FDR were averaged over the same period of time before comparison with EMS performance data was made. Although an enormous amount of data were collected from the ground runs and the flight trial, in particular by the continuous recordings of the DBA, a small part of the data was enough to perform the validation. The engine data parameters that were validated are grouped in Fig. 5. EMS Engine Data Engine Usage Engine Condition Cycles Pressures Temperatures Operating Time Power Torque Life Usage Indices Fuel Flow Speeds Times at Usage Zones Ram Pressure Ratio Propeller Blade Angle Peak Counts Power Lever Angle Vibrations Fig. 5: List of Engine Monitoring System data that were validated EMS validation The engine data recorded by the EMS during the trials, and selected for use in the validation exercise, were examined for any range check discrepancies using the values specified in the Original Equipment Manufacturer (OEM) documents and no problems were found. Because the operating aircraft engines are dynamic systems, it was expected that the engine data collected would show inherent variability. This is shown in Fig. 6 for some engine data recorded
over a period of one second. Although small, it was considered as a possible cause of discrepancies in the validation process when comparing values from asynchronous sources. Fig. 6: Percentage variation in engine data values (DBA) during 1 second at cruise The EMS engine usage data validation demonstrated that: Engine operating times were correctly calculated, by comparison with other data showing time between engine on and off (Table 1). Engine cycles were correctly calculated, by comparison with the trials test plan that was strictly adhered to (Table 2). Total engine cycles and total operating times stored in the EMS were incorrect; this has been found to be due to a procedure and software problem that will be fixed. Times at each of the eight usage zones were correctly calculated, by comparison with calculations made using DBA data (Fig. 7). Peak counts for the speeds were correctly counted, as determined from calculations using DBA data. It was confirmed that Life Usage Indices were incorrectly calculated, and the OEM has been developing a solution. The EMS engine condition monitoring data validation demonstrated that: Engine performance data at take-off were valid, by comparison with averaged FDR and DBA data (Fig. 8). Engine performance data at cruise were valid, by comparison with averaged FDR and DBA data. Engine snapshot data from ground running and flight (Fig. 9) were valid, by comparison with cockpit images, FDR and DBA data. Table 1: Validating engine operating times (flight trial) Total engine run time (hours) Diff Diff Engine EMS DBA (seconds) % 1 1.398 1.406-26 -0.51 2 1.369 1.376-27 -0.54 3 1.355 1.362-26 -0.54 4 1.383 1.389-23 -0.46
Table 2: Validating engine cycles (ground run) Engine EMS Cycles Actual Cycles 1 2 2 2 2 2 3 1 1 4 1 1 Fig. 7: Validating time at each engine usage zone for engine 1 Fig. 8: Validating engine performance data at take-off for engine 1 Fig. 9: Validating engine flight snapshot data for engine 1
Conclusion The Engine Monitoring System (EMS) engine usage and engine condition monitoring data have been validated using data obtained from the aircraft cockpit display screens, the Data Bus Analyser and the Flight Data Recorder, during engine ground running and flight trials. The validation exercise demonstrated that the EMS can accurately provide data for oncondition maintenance of the military aircraft engines. It was demonstrated that the EMS correctly calculates the number of engine cycles and engine operating times during a mission that can be used to track engine component lives. The total usage values and the Life Usage Indices recorded in the EMS were incorrect and the Royal Australian Air Force has actions in place to resolve this. Acknowledgements The author wishes to acknowledge all the ADF personnel and contractors, and DSTO personnel involved in the planning and execution of the trials. References 1. MIL-STD-1783 (USAF), 1984, par 5.17, p. 17. 2. CAA Condition Monitored Maintenance an Explanatory Handbook CAP 418. CAA London, July 1978.