Because they are also very expensive helicopters & the odds of having a dual engine failure with modern turbines are pretty slim, most companies have decided it's not worth the risk of damage to practice autos to touchdown - it's a purely economic decision. They do still practice them with a power recoveryquadrirotor said:don't forget that for most twin engines high tech. helicos, autorotation is a forbidden practice!!!!
Here is an idea; Safety FuelI would think that when you run out of fuel both engines would stop. In the NTSB reports running out of fuel is common in aircraft.
A couple of comments, for the fun of it;If each engine has a failure rate of once per 1000 hrs, then both engines will fail every 1 million hours, on average.