The Aircraft Condition Monitoring System (ACMS) allows the automatic broadcast of APU Trend Monitoring parameters. These parameters are stored in the Data Memory Module (DMM) of the APU. The APU Electronic Control Box (ECB) transmits these data to the ACMS system each time the APU ECB is powered. The following paramteres are used for the Trend Monitoring of the APU:
- APU Hours
- APU Cycles
- CT5ATP – Corrected APU EGT during Main Engine Start (MES)
- CPTATP – APU Bleed Pressure during MES
- IGVATP – IGV Position during MES
These parameters can be transmitted automatically through an ACMS report via ACARS to the airline operational control center or could be printed from the cockpit. If the parameter CT5ATP reaches 625°C the APU requires a closer monitoring. If CT5ATP reaches 660°C the APU will experience gradual IGV cutbacks.