[Orv Neisingh]

Over the years I have experienced several failures related to the ACIS system on the Rotorway. Dave W. in California is one of my former students for both hover and altitude training. He had just completed his 100 hour inspection and asked me to give him some more autorotation training. I informed Dave that the ACIS engine often burns through a piston around the 100 hour mark due to detonation. I went out to CA and on our second auto the engine started to run rough, as we set it on the ground we noticed a huge puddle of oil pouring out of the oil tank vent tube. Piston number one had a hole burnt through it causing combustion gasses to pressurize the crank case and force the oil out of the engine and tank.