Mastering the Honeywell Two-Button Digital Engine APU Controller

Mastering the Honeywell Two-Button Digital Engine APU Controller A critical APU troubleshooting tool By John Casey April 2000 On a number of aircraft, a Digital Electronic Control Unit controls the Auxiliary Power Unit (APU). The...


On the Citation X, one can change the APU Data and erase faults while in DISPLAY mode (only the battery switch "ON") and the ECU will not save the changes. The ECU must be powered on by the APU Master switch before updating can take place. This should be remembered if trying to change data and the ECU is in DISPLAY mode.

Remember, isolate the error code(s) and refer to the applicable manual for fault error codes and maintenance tasks. Honeywell Aerospace Academy will soon complete an extensive electronic simulation for the ECU installed in the Cessna Citation X. The training simulation, although designed to be instructor led, will include a comprehensive instruction text box to help lead the student through the course.

Remember, take the time to learn and understand the ECU — being able to use the unit correctly will help to isolate faults and reduce operating costs.

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