Helicopter loses control in self-generated vortices during hover taxi

Casualties unknown • Loss of control during hovering, SNIAS SE 313 B (Alouette II), Koudekerk aan den Rijn, NL

An Alouette II helicopter sustained heavy damage after encountering its own wake turbulence while performing a hover taxi in Koudekerk aan den Rijn.

What happened

On June 26, 1999, at approximately 18:00, an Alouette II helicopter, registration PH-NSW, was conducting passenger sightseeing flights near Koude kerk aan den Rijn. After completing a standard approach, the pilot decided to perform a 270-degree hover taxi to reposition the aircraft. This maneuver was intended to ensure the pilot maintained a clear view of spectators on the landing field.

During this low-altitude maneuver, the aircraft suddenly experienced a loss of control. The pilot felt a physical impact on the cyclic, followed by a rapid descent. Despite attempts to increase collective pitch, the aircraft's right skid struck the ground, causing the helicopter to tilt onto its right side. The impact resulted in broken rotor blades and the start of a small fire, which was quickly extinguished by ground crew members. There were no injuries among the pilot or the four passengers on board.

The investigation

Investigators examined the flight conditions and the aircraft's mechanical state. The aircraft was found to be airworthy, with its weight and center of gravity within legal limits. The pilot, who had approximately 450 flight hours, had been operating for the day since 08:58, with a total of two hours of rest distributed throughout the day. While the flight hours complied with legal duty and rest regulations, investigators noted that fatigue could not be ruled out as a contributing factor.

Technical analysis, supported by findings from the Netherlands Aerospace Laboratory (NLR), focused on the atmospheric conditions. The day was characterized by very light winds and minimal turbulence, creating a stable atmosphere that allowed air vortices to persist.

Findings

  • The primary cause of the accident was a significant reduction in lift and controllability caused by the helicopter flying into its own wake turbulence.
  • The stable atmospheric conditions and low wind speeds allowed the vortices generated by the aircraft to remain active.
  • The pilot was unable to respond adequately to the sudden loss of control, leading to the right skid striking the ground.
  • The aircraft sustained heavy damage, including broken rotor blades.

Probable cause

The helicopter encountered its own self-generated air vortices, which caused a sudden loss of lift and maneuverability that the pilot could not counteract.

Frequently asked questions

What happened in the null aircraft accident near Loss of control during hovering, SNIAS SE 313 B (Alouette II), Koudekerk aan den Rijn, NL?

An Alouette II helicopter sustained heavy damage after encountering its own wake turbulence while performing a hover taxi in Koudekerk aan den Rijn.

What aircraft was involved and where did it happen?

The accident on null involved a aircraft, at Loss of control during hovering, SNIAS SE 313 B (Alouette II), Koudekerk aan den Rijn, NL.

What was the probable cause of the accident?

The helicopter encountered its own self-generated air vortices, which caused a sudden loss of lift and maneuverability that the pilot could not counteract.

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