The purpose of this AIR is to document some of the valuable lessons learned from several developmental and operational turbine engine monitoring programs. This AIR is not intended to be used as a standard or legal document but rather to provide an objective statement of the more important lessons learned during the development and operation of engine monitoring systems with widely varying operational requirements. It is through the use of ARP 1587 'Aircraft Gas Turbine Engine Monitoring System Guide,' and SP-478 'Aircraft Gas Turbine Engine Monitoring Systems,' an awareness of prior lessons learned and a clear definition of engine operational maintenance concepts that future engine monitoring systems can be developed to meet the specific needs of the user.