This SAE Aerospace Information Report (AIR) presents metrics for assessing the performance of prognostic algorithms applied for Engine Health Management (EHM) functions. The emphasis is entirely on prognostics and as such is intended to provide an extension and complement to such documents as AIR5871, which offers information and guidance on general prognostic approaches relevant to gas turbines, and AIR4985 which offers general metrics for evaluating diagnostic systems and their impact on engine health management activities.This Aerospace Information Report (AIR) has been superseded by the document AIR7999, "Diagnostic and Prognostic Metrics for Aerospace Propulsion Health Management Systems." AIR7999 consolidates and expands upon the contents of this document (AIR5909) plus AIR4985, "A Methodology for Quantifying the Performance of an Engine Monitoring System." As such, AIR7999 provides a single comprehensive document on diagnostic and prognostic metrics for aerospace propulsion health management systems making the contents of AIR5909 and AIR4985 redundant and unnecessary. This document consolidation strategy was agreed to by the SAE E-32 Aerospace Propulsion Systems Health Management Committee as part of the Committee's Master Plan.