Engine power loss during autorotation recovery leads to hard landing in CH7 Kompress

Casualties unknown • FR

An instructional flight in a CH7 Kompress ultralight helicopter ended in a heavy landing at Arcachon La Teste-de-Buch after an engine failure occurred during a power application.

What happened

On May 5, 2014, an instructor and a student were conducting an advanced instructional flight in a CH7 Kompress C2 ultralight helicopter, identified as 33-AKR. The flight involved practicing autorotation exercises with engine recovery at the end of the maneuver. During the second exercise, the instructor took control of the aircraft to adjust the flight path before the final turn.

As the aircraft reached approximately 150 feet and the instructor attempted to apply power to transition from autorotation back to normal flight, the available engine power significantly decreased. The engine failed, triggering audible and visual warnings. Due to the low altitude, the instructor was unable to recover rotor RPM and chose to flare the aircraft to cushion the impact. The helicopter struck the unpaved runway at Arcachable La Teste-de-Buch with a high pitch attitude, causing the aircraft to skid and come to a halt on its skids. The ULM sustained very heavy damage.

The investigation

Investigators examined the wreckage and found significant deformation in the rear right skid arch and damage to the tail boom, including broken mounts for the tail boom supports. Traces of contact between a main rotor blade and the tail boom were also identified.

Technical analysis of the Rotax 914 UL engine revealed that a loop in one of the ignition harness bundles had melted against an exhaust manifold. This contact stripped the insulation from two electrical wires, causing electrical arcing. The investigation determined that the configuration of the spark plug cables and the protective synthetic sleeve made contact with the hot engine component possible.

Findings

  • The engine power loss was caused by a short circuit in the ignition system, where the melting of the ignition harness wires interrupted the power supply to two cylinders.
  • The engine design allowed the spark plug cables or their protective sleeve to come into contact with the exhaust manifold.
  • The instructor's sudden takeover of the controls to adjust the trajectory, combined with the unexpected engine failure at low altitude, likely reduced situational awareness regarding rotor RPM monitoring.
  • The engine failure occurred precisely during the high-power demand phase of the engine recovery maneuver.

Probable cause

The primary cause of the accident was a loss of engine power during the transition from autorotation to powered flight, resulting from an ignition system short circuit caused by wires contacting the hot exhaust manifold. This was compounded by the unexpected nature of the failure at a low altitude during a maneuver transition.

Frequently asked questions

What happened in the 2014-05-05 aircraft accident near FR?

An instructional flight in a CH7 Kompress ultralight helicopter ended in a heavy landing at Arcachon La Teste-de-Buch after an engine failure occurred during a power application.

What aircraft was involved and where did it happen?

The accident on 2014-05-05 involved a aircraft, registration 33-AKR, at FR.

What was the probable cause of the accident?

The primary cause of the accident was a loss of engine power during the transition from autorotation to powered flight, resulting from an ignition system short circuit caused by wires contacting the hot exhaust manifold. This was compounded by the unexpected nature of the failure at a low altitude during a maneuver…

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