Thanks for many comments. You confirmed my opinion the more often the better trend monitoring but there is an optimization point what is the best interval... We perform PAC in interval 20-25FH on EC135 but wondering to do it quite more often. On EC135 we also have an option to do In-flight Power Check at 60% TRQ but as I remember only Power Assurance Check at 75% on the ground is required by EMM for trend monitoring.
One PAC takes about 8-12min - 1.5-2min stablization for each engine on the ground so it is quite a bit of time to do it daily I think. In the past stabilization was set at 1min for each engine but then we had many problems with enough time for stabilization which led to inaccurate results. The engineering team during data analysis had even problems to find the stabilization period in the check caused by windy conditions, unintended pilot moves, yaw etc. So we've increased the time and results are much better now.
How are you doing with stabilization and results accuracy for PAC on the ground? Especially those, who do it every day. Do you have similar problems?