henra said
and stop the rotor in a frighteningly short time.
In support of that I noticed the following.
Regarding a different EC135 incident[1] the NTSB report said:
1741:48, the main rotor RPM had decreased to 73 percent.
...
a rapid increase in main rotor rpm, to about 125 percent, which occurred at 1741:53
...
At 1741:56, the pilot transmitted, "mayday mayday, our engines are out, we're going down."
125% is 3 times the Knietic Energy of 73% (square law)
It seems that aerodynamic forces can change the rotor speed very rapidly (at least upwards).
With the same input force (or is it power, or are they the same thing?) it would go from 0% to 73% (or the reverse) in about a second and a half.
[1] NTSB Report
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