Incident Details
During autorotation practice with a power recovery, a Schweitzer 269C-1 helicopter impacted the runway with excessive force. The left skid collapsed and the helicopter rolled onto its left side.
Pilot Accounts
The student pilot reported that as main rotor rpm increased, he attempted to raise the collective. The collective initially did not move, then moved fully upward. The main rotor blades stalled, and the helicopter struck the ground hard. The flight instructor stated that the student raised the collective; the instructor immediately lowered it and added power but could not prevent a hard landing. The instructor noted that the engine responded to his inputs.
Control System Examination
Inspection of the flight controls found that the collective and main rotor swash plate operated freely with no evidence of jamming or resistance. No loose objects were discovered in the helicopter that could have restricted collective movement.
Engineering Assessment
An engineering test pilot from Schweitzer stated that a momentary pop-up of the collective to full up and back down in less than one second would not cause blade stall. Blade stall would require the collective to be held fully up for three seconds or more. The flight instructor reported that his hand was near the collective but not on it during the event.