What happened
On September 15, 2012, a privately owned Eurocopter EC120B, registration JA120H, was conducting a leisure flight from Tokyo Heliport to a temporary helipad in Kujukuri Town, Chiba Prefecture. The flight carried the pilot and four passengers.
Upon the initial arrival at the Kawashima temporary helipad, the pilot noticed the aircraft was not level. To correct this, the pilot performed a brief hover, moved the aircraft approximately one meter to the right, and resettable on the ground. After the passengers disembarked, the pilot returned to the aircraft at approximately 15:30 to prepare for the return flight. Following a standard exterior inspection, the pilot re-entered the right seat and started the engine.
As the helicopter became light on its skids during the takeoff sequence, the pilot applied small pedal inputs and sensed that the skids were caught. In an attempt to verify the status of the skid restraints, the pilot applied small left and right rudder inputs to wiggle the aircraft. During this maneuver, the pilot unintentionally increased the collective pitch. This caused the Eurocopter EC120B to roll over to the right and rearward. The incident resulted in two minor injuries to passengers and significant damage to the aircraft, including the separation of all three main rotor blades at the root fitting.
The investigation
The JTSB investigation examined the aircraft's components, including the engine and flight controls, finding no mechanical anomalies other than the damage sustained during the rollover. The investigation focused on the condition of the temporary helipad, which consisted of a sand base covered with trimmed grass.
Investigators noted that the ground was soft enough for the skid rear ends to penetrate the grass roots. Evidence of a small patch of turf being displaced was found where the aircraft had resettled. The investigation also reviewed the pilot's flight history, noting that while the pilot had performed 19 previous operations at this specific site, he had no prior experience performing a post-landing relocation at this helipad.
Findings
- The right skid rear end likely slid beneath the grass roots during the pilot's attempt to level the aircraft after the initial landing.
- The pilot failed to detect that the skid was trapped during the pre-flight exterior inspection.
- The pilot continued the takeoff sequence despite sensing resistance in the skids.
- The primary cause of the rollover was the pilot unintentionally raising the collective pitch while attempting to wiggle the aircraft with rudder inputs after sensing the skids were caught.