Rotorway Helicopter Destroyed After Striking Power Lines in Oulu

Casualties unknown • FI

A private Rotorway Exec 90C helicopter crashed in the Pyhäjoki river after colliding with 20 kV power lines during a low-altitude flight.

What happened

On August 16, 1997, a private flight involving a Rotorway Exec 90C helicopter, registration OH-XHV, resulted in the total destruction of the aircraft near Oulu, Finland. The pilot was conducting a training flight along the Pyhäjoki riverbed, flying at an altitude significantly below the minimum required height.

While following the river, the pilot observed the glint of 20 kV power lines approximately 40 meters ahead. In an attempt to avoid the obstacle, the pilot performed a sudden, aggressive control input, pulling the cyclic fully aft to convert airspeed into altitude. This maneuver failed to gain sufficient height, and the helicopter struck the lines. The impact severed two of the wires and struck the landing gear and skid.

The force of the sudden control input caused the main rotor hub's flapping limits to fail. This allowed excessive flapping, which led to a rotor blade striking the tail boom, causing the boom to break off. The impact also stripped the cockpit canopy from the airframe. The crippled aircraft continued flying uncontrolled for approximately 65 meters before impacting the riverbed in a nose-down attitude. The water depth was only about one meter, allowing the pilot and passenger to escape the wreckage and reach the shore with only minor injuries.

The investigation

The investigation examined the aircraft's structural failure, the pilot's flight maneuvers, and the circumstances leading to the low-altitude flight. Investigators analyzed the wreckage, noting that the primary rotor hub's flapping limiters were made of relatively fragile material compared to type-certified helicopters. The investigation also reviewed the pilot's credentials, finding that his helicopter pilot license had expired approximately two months prior to the accident.

Findings

  • The pilot was flying well below the minimum required altitude, which directly enabled the collision.
  • The pilot lacked the necessary instinctive skills to execute an effective emergency altitude change due to insufficient training in such high-stress scenarios.
  • The aggressive control input caused the failure of the rotor flapping limiters, leading to the catastrophic structural failure of the tail boom.
  • The pilot was operating with an expired helicopter pilot license.
  • The passenger had not been sufficiently instructed on how to release the seatbelts in an emergency.
  • Post-accident blood tests confirmed the pilot had consumed alcohol after the flight to treat a 'hangover.'

Probable cause

The primary cause of the accident was the pilot flying below the minimum altitude and failing to avoid the power lines. This was compounded by inadequate training for managing high-stress emergency maneuvers and a sudden control input that caused the rotor system to strike the tail boom.

Frequently asked questions

What happened in the 1997-08-16 aircraft accident near FI?

A private Rotorway Exec 90C helicopter crashed in the Pyhäjoki river after colliding with 20 kV power lines during a low-altitude flight.

What aircraft was involved and where did it happen?

The accident on 1997-08-16 involved a aircraft, registration OH-XHV, at FI.

What was the probable cause of the accident?

The primary cause of the accident was the pilot flying below the minimum altitude and failing to avoid the power lines. This was compounded by inadequate training for managing high-stress emergency maneuvers and a sudden control input that caused the rotor system to strike the tail boom.

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