Originally Posted by
Mr @ Spotty M
You will have to compare its clock reading with the actual Flying Hours.
That would be the most accurate method.
That would be of no use. APU's are changed many times during the a/c's life. For example, this week I had a check on an aircraft with about 30000 hours, the APU had 5000 hours and 6000 cycles (approximated); another airraft with same hour life had an APU with 600 cycles and 280 hours.
I would say on an average flight the APU is used 10 minutes before and 10 minutes after engine running. Maintenance most of the time also add a fair amount of APU use.