Eurocopter AS-350-BA N906BA accident near Linden, New Jersey

Probable cause

The flight instructor’s delayed remedial action (flight control inputs) during a practice autorotation/run-on landing resulting in fracture damage to the main rotor system Starflex.

NTSB analysis

The flight instructor was monitoring the student pilot during a 180-degree autorotation as part of the flight training. The maneuver was entered at 700 feet above the ground and at 100 knots. Once the intended spot was made for the 'power-on' recovery, the flare was started. As the flight instructor advanced the fuel flow control valve into the flight position, the helicopter started to settle and the low rotor speed horn came on. The flight instructor took over the controls advising the student pilot that it was going to be a run-on landing. During the landing, while in the ground run, the nose of the helicopter pitched forward as the skids dug into the mud. The flight instructor pulled back on the cyclic to prevent the blades from contacting the ground. The helicopter came to rest in the upright position in the grassy area. Post accident inspection of the helicopter’s main rotor system revealed that the 2,167 hours time in service Starflex component had two of its three arms fractured. Examinations of the fracture surfaces revealed no indications of any pre-existing damage to the areas. The fractures were consistent with overstress and unusual loads, which were produced during abrupt flight control inputs with low main rotor RPM.

Text from the NTSB. Open the NTSB docket for MIA08LA199 for the full record.