EBCAU is a independant Eurocopter supplied computer that governs the free turbine between 98 and 102 perc or somethingnlike that utilising a seperate independant valve from the stepper motor metering valve and electronic logic in the ASU 3 situated to the right of the coplts feet. The EBCAU is automatically activated by the FADEC incase of total stepper motor or metering valve failure which will be sensed bynthe resolver or both comp fails. No action req by the pilot. This is for the 2B1 and 2 D, the 2B will unlock the sliding lock on the throttle to allow manual control. In both cases the engine comp stops the metering valve where the failure occured thus the N1 and the EBCAU or throttle can control free turbine speed around that position.
Overspeed control is called the pilot on the singles. Not sure how the DECU's will deal with it and not going to try and see what happens if the MGB input shaft fails.