The fatal crash of a Robinson R44 helicopter (4X-BDM) in Israel in November 2009 was the result of the failure of one of the main rotor blades, according to the report of the Israeli air accident investigator.

Yitzhak Raz, the chief accidents investigator in the Israeli ministry of transport, says the failure was caused by a combination of erosion where the outer skin of the blade is connected to the blade's main spar, and separation of the skin from the "honeycomb" filling.

Raz says: "This combination caused the sudden separation of most of the blade's skin from its spar." The loose blade then cut through the tail assembly of the R44, separating it from the fuselage.

The report suggests: "There is real probability that some of the similar accidents in recent years that involved that type of helicopter were caused by a similar failure process."

The R22 and R44 have suffered multiple accidents, especially in their early days, involving the main rotor damaging the tail boom, but this was often attributed to the intolerance of the design to rapid movement of the cyclical control, which tended to destabilise the rotor blades of these very lightweight types.

Such events were often linked to the use of the types for training, or by entry-level owner/pilots who did not make allowances for this vulnerability.

All on board the helicopter were killed when it crashed into the Mediterranean.

Source: Flight International