The link in the quote discusses low rotor RPM, and the ‘line’ mentioned is this one:
Yesterday a helicopter crashed in Spokane Valley, Washington. Link.
A 13-year-old witness said, ‘It was making a sound like a quarter in a washing machine, then there was a loud pop,” and the craft started spinning.’
Of course the cause of the crash will have to be determined by investigators, but it sounds like a classic low rotor RPM situation that occurred after a loss of power. The ‘quarter in a washing machine’ comment makes me suspect a blown jug. Perhaps there was a failure of a shaft, but I’m guessing that that would cause the spin before the boom chop. If the sequence is as the boy described, it sounds like the shaft was turning the tail rotor (and thus preventing the spin) until the chop. Having no other information other than there was a mechanical problem and a boom chop, my hypothesis is as follows: The aircraft suffered a loss of power. The student pilot did not lower the collective lever rapidly enough to maintain rotor RPM. The rotor stalled and severed the tail boom. The pilot was, as the Safety Notice states, ‘doomed’.
The R22 has a low-inertia rotor system. That is, it’s lightweight and doesn’t have the mass to keep turning for very long in the event of a power failure. It is critical to lower the collective immediately to reduce the pitch of the rotor and enter autorotation. You have like a second, so pilots are trained to the point where the response is automatic – or should be. Entering autorotation after a power failure also includes canceling inputs to the anti-torque rotor, as there is no longer any torque (except for friction) to counteract.
I used to have in my possession a video shot from a tanker of an MH-53 that finished mid-air refueling, then proceeded to chop off the business end of the refueling probe with the rotor. Kinda funny to watch; I’m sure there were several soiled poopy suits onboard, and suspension of flying privileges for the flight crew once they landed.
I’m an aviation (fixed-wing) accident enthusiast, so to speak, and I couldn’t really follow what you were saying until you posted the video–that clears it up. I had a hard time picturing it because in my mind, it should be physically impossible for that to happen. I would have thought there was some safety feature in helos that would prevent that, especially after what you said about the minimal reaction time required for a power loss.