Directly from the S-76C++ flight manual
The NO. 1 or NO. 2 ENG OUT - RESET TONE warning light on the master
warning panels (Figure 1-93) will go on and an alternating tone (550 Hz and 700
Hz) will be heard in the headset when the DECU engine failure detection logic
detects an engine out condition for that engine or when N
1 for the corresponding
engine drops to 48%