From old 212 daze:
High RPM High power on one engine = HIGH SIDE GOVERNOR FAILURE.
High Rotor RPM , High power on one engine, very low or even idle power on the other = High Side Gov failure on the high power engine. High power engine may not respond to throttle movement even if reduced to idle and you will have either shut down the high power engine or select manual governor as per the RFM ECL. NB. Do not select manual gov except when the throttle is on the idle stop.
In both cases Rotor RPM control is the first priority.
Low RPM low power on one engine = LOW SIDE GOVERNOR FAILURE.
Low Rotor RPM with high power demand on one engine and low power on the other = Low side governor failure on the low power engine. Reduce throttle to idle and select manual governor on the low power engine as per RFM ECL. NB. Do not select manual gov except when the throttle is on the idle stop..
In both cases Rotor RPM control is the first priority.
Once on the ground DO NOT lower the collective immediately as you may massively overspeed the rotor system. Best to set idle N1 on the failed engine or even shut it down before lowering the collective. Proceed slowly and think about what you are doing.