Title : A Computer Based Instructional Environment for Machine Condition Monitoring in Engineering Education

The US Army is actively transforming its Aviation Maintenance from current practice to one where maintenance action is based on evidence of need using an increased number of embedded sensors and diagnostic equipment. Several demonstrations of HUMS system capabilities have been conducted to adopt these systems to the US Army environment and to identify the costs and risks. Benefits expected from this transformation are improved readiness, reduced maintenance burden, and information and analysis necessary to optimize the maintenance supply chain. The US Department of Defense defines CBM+ as a set of maintenance processes and capabilities derived primarily from real-time assessment of weapon system condition obtained from embedded sensors and/or external test and measurements using portable equipment. For the military rotorcraft, this capability is associated with Health and Usage Monitoring Systems. The soldier will perceive the effective implementation of CBM as a reduction in teardowns and subsequent inspections (sometimes visual, sometimes eddy current, & sometimes ‘feel for roughness’), a reduction in replacement of parts that are fully airworthy as determined by this new criteria, a better indication of flaws in components with poor or difficult inspect-ability, and an overall improvement in readiness and safety. One of the tradeoffs that is considered in implementing a fleet-wide application of new capability, is the determination of when added complexity and cost exceed the perceived value of the system. Cost and benefit studies for systems of embedded sensors have been conducted with significant variation in perceived benefit. Demonstrated Effectiveness of Vibration-Based Diagnostics Condition Indicators (CIs) form the basic unit of information used to guide the transformation to condition based maintenance. A CI time history is an indication of the progression of a specific fault on its way to failure. On the rotorcraft drive system CIs are based on well documented signal analysis of vibration sensors. The US Army has over 200 helicopters with embedded vibration monitoring systems currently acquiring CIs. Based on observed evidence where the value of specific CIs have been correlated to specific material conditions that represent flaws that should be removed from the aircraft, changes to the allowable maintenance practices (maintenance credits) have been allowed by the airworthiness authority. A specific example is given for the AH-64, Apache main rotor swashplate. This component must be removed after 2250 flight hours. But, after 1750 flight hours, a physical inspection of the bearings must be made every 50 hours. At a point where we have approximately 20,000 flight hours of CI data collected for the swashplate on several aircraft, the comparison of different aircraft is shown. A yellow level represents a statistically established value for attention. The trend of swashplate CI, based on spectral energy, for Apache Tail 460 clearly is an outlier to the total set of data collected. Swashplate CI Trending Analysis Analysis of the spectral information collected that support the condition indicators for the Tail 460 and another “normal” aircraft are shown below. A Updated 5 Mar 07 principal peak of energy is seen in data from the outlier swashplate that does not exist on a normal aircraft. In addition the relative frequency of sideband energy is related to the specific geometric configuration of the swashplate bearing assembly. It should be noted that this swashplate was inspected (as prescribed after 1750 hours) and not found to be faulted. The swashplate was removed from Tail 460 and disassembled. The results of the inspection revealed a material condition identified below. Evidence of corrosion, grease contamination, broken cage, and surface degradation of the balls are seen. Based on this evidence, an allowance (maintenance credit) for those aircraft equipped with the monitoring system was issued to replace the requirement for the post 1750 hour inspection. Summary The US Army has historically used Condition Indicators to get back to ‘Baseline Risk’ when faced with an unanticipated failure in the field which effects Airworthiness. We are on a path to implementation of new condition based maintenance practices using matured condition evaluation technology. Finding methods of implementing simplified and timely maintenance practices based on the evaluation of on-board vibration sensors signal output is a near-term CBM payoff for drive system components. The full presentation will show further examples and some of the processes used in implementing maintenance changes based on available modern diagnostics capabilities and will discuss how the added accessible information derived from modern on-board diagnostic systems has helped to simplify this process. Updated 5 Mar 07 MFPT 61 ABSTRACTS SESSION # 1A Session Title: Maintenance Presenter: Qiao Sun Organization/Affiliation: The University of Alabama Paper Title: A Computer Based Instructional Environment for Machine Condition Monitoring in Engineering Education Principal Author(s): Qiao Sun Copauthor(s): Sally A. McInerny