I can't remember if the backup pump switch was supposed to be in "ON" or "AUTO" for this check (it's been ~8 years
since I've flown a 60), but a couple of my friends were in a hover practicing SAR procedures when their LDI did its thing... IIRC* the spec for the backup pump to go from off to full pressure is 0.5 seconds... meantime the tail rotor had enough time to relax its pitch somewhat and allow the aircraft to yaw ~90 degrees with a loud noise ("like the aircraft got hit by a sledgehammer" were my friend's words)... then once the tail rotor had proper hydraulic power again I think there was a bit more yaw. Note, the FCF check was nothing like this.
The guys were just happy this happened in day/VMC! Fun times.
*Some of my systems minutia might be off, but the loud noise + huge yaw kick in a coupled hover details are right.