Modern commercial aircraft engine maintenance includes a form of threshold testing on monitored engine parameters. In most cases the thresholds used to monitor the respective parameters are determined by the engine manufacture and do not take into account an aircraft's engines actual usage. In addition, thresholds set by the engine manufacture are set to provide a warning for the most severe cases in which an engine failure may occur if the threshold is reached. More importantly these thresholds impact the engine maintenance and management procedures used by the commercial airlines. Though useful, the thresholds given do not provide enough information for daily operation and maintenance planning. What is needed is a ldquoworst caserdquo analysis which can provide an improved insight on the behavior of monitored engine parameters. Presented is an investigation of applied ideas and concepts from Extreme Value Theory to engine health monitoring.