Tail rotor effectiveness loss leads to emergency landing of Eurocopter AS350 B2

Casualties unknown • Seixal, PT

An Eurocopter AS350 B2 experienced an uncommanded yaw during aerial filming, resulting in an emergency autorotation landing and substantial aircraft damage.

What happened

On January 10, 2011, an Eurocopter AS350 B2 helicopter, registered CS-HFP, was performing aerial filming for a radio and television news station. While en route, the pilot experienced an uncommanded yaw to the left. Suspecting a mechanical failure in the tail rotor, the pilot decided to perform an emergency landing using the autorotation procedure.

To regain control and stop the aircraft from spinning, the pilot reduced the collective pitch and applied forward airspeed, effectively disengting the engine from the drive system. However, the pilot did not shut down the engine after entering autorotation, which is the recommended procedure when tail rotor failure is suspected. During the descent, the rotor speed exceeded normal limits. As the pilot attempted the final flare to reduce the descent rate, the engine—which was still operational—caused the rotor speed to return to nominal RPM. This sudden increase in power, combined with a late flare, caused the tail skid to strike the ground with significant force, leading to a loss of control and substantial damage to the aircraft. There were no injuries to the crew or passengers.

The investigation

The GPIAAF investigation confirmed that the aircraft was properly maintained and within weight and balance limits. The investigation found no evidence of mechanical defects, malfunctions, or pilot incapacitation. The aircraft was equipped with a rotor speed and engine data recorder, though such equipment was not required by current regulations. The investigation focused on the aerodynamic phenomenon of Loss of Tail Rotor Effectiveness (LTE) and the pilot's execution of the emergency landing.

Findings

  • The primary cause of the accident was loss of control in flight due to the loss of tail rotor aerodynamic effectiveness, followed by a loss of control during touchdown caused by a tail ground strike.
  • The flight characteristics associated with aerial filming, such as low-speed turns or hovering at altitude, contributed to the occurrence of LTE.
  • The pilot failed to recognize the situation as LTE, instead assuming a mechanical failure and proceeding with a full autorotation.
  • A late flare during the touchdown phase led to the tail strike.

Probable cause

The accident was caused by the loss of aerodynamic effectiveness of the tail rotor during low-speed flight maneuvers, compounded by the pilot's failure to recognize the phenomenon and the subsequent tail ground strike during a late flare during the emergency landing.

Frequently asked questions

What happened in the 2011-01-10 AS350 B2 accident near Seixal, PT?

An Eurocopter AS350 B2 experienced an uncommanded yaw during aerial filming, resulting in an emergency autorotation landing and substantial aircraft damage.

What aircraft was involved and where did it happen?

The accident on 2011-01-10 involved a AS350 B2, registration CS-HFP, at Seixal, PT.

What was the probable cause of the accident?

The accident was caused by the loss of aerodynamic effectiveness of the tail rotor during low-speed flight maneuvers, compounded by the pilot's failure to recognize the phenomenon and the subsequent tail ground strike during a late flare during the emergency landing.

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