As the pilot lifted the helicopter into the hover he felt an unusual vibration and was unable to prevent an immediate turn to the left. Shortly afterwards the nose of the helicopter pitched up and down sharply and the tail rotor guard struck the ground two or three times. The guard broke and portions of the tail rotor blades were torn off. The helicopter then landed heavily, damaging the landing skid. Engineers found no significant fault with the helicopter. It is highly probable that the pilot took off with the hydraulic assist to the cyclic control inadvertently selected off. This helicopter has an electrical on/off hydraulic switch which is not common on the Bell 47-G2. The pilot was more familiar with the mechanical on/off system. He may have been distracted from completing his pre-take-off checks by explaining them to the passenger. With hydraulics selected off, feed back forces occur through the cyclic control; this could be felt as an unusual vibration. Because of the feed back forces, the pilot began to overcontrol the helicopter thereby causing him to channelize his attention to the cyclic control to the detriment of directional control. Although the pilot had been trained in "hydraulics off" emergency procedures in flight he had never before experienced lifting a helicopter into the hover with the hydraulics selected off.
