This Aerospace Information Report (AIR) describes a Limited Engine Monitoring System that can be used by the flight crew or the maintenance staff@ or both@ to monitor the health of gas turbine engines in aircraft. This AIR considers monitoring of gas path performance and mechanical parameters@ and systems such as low cycle fatigue counters and engine history recorders. It also considers typical measurement system accuracies and their impact. This AIR is intended as a technical guide. It is not intended to be used as a legal document or standard. AIR 1873 supplements ARP 1587@ Aircraft Gas Turbine Engine Monitoring System Guide