What happened
On November 28, 2007, an Eurocopter AS 350 BA, registration EC-FOA, was performing aerial inspection work on a high-voltage power line near Elche, Spain. The crew, consisting of a pilot, a line technician, and a camera operator, had successfully inspected two towers before approaching the third.
As the pilot reduced airspeed to transition into a hover, the engine suddenly stopped. The pilot heard the main rotor low RPM warning and noted the engine had ceased operation. The aircraft began a rapid descent. The pilot managed to maneuver the helicopter away from the power lines, but the aircraft ultimately impacted a mandarin grove with a high vertical velocity and minimal horizontal speed.
While the aircraft remained upright, the impact was severe, causing major structural damage to the fuselage, landing gear, and tail rotor. All three occupants sustained injuries, primarily to their backs, but were able to exit the aircraft following the impact.
The investigation
Investigators examined the engine, fuel system, and flight data. A spectrum analysis of the flight audio confirmed that all engine and rotor parameters were normal until the moment of power loss, after which the rotation rates of the compressor and main rotor decreased rapidly, consistent with an engine stoppage.
Detailed inspections of the Turbomeca Arriel 1B engine, including borescope and bench tests, found only minor anomalies that were insufficient to explain the sudden loss of power. The fuel was tested and found to be within specifications, with no evidence of contamination.
Investigators also reviewed the aircraft's flight envelope using the height-velocity chart. They determined that at the time of the engine failure, the aircraft was flying at an altitude of approximately 50 feet with a low translational speed of about 15 knots. This position placed the helicopter within the restricted area of the height-velocity chart, where the combination of low altitude and low speed does not provide sufficient margin for a safe emergency landing in the event of an engine failure.
Findings
- The primary cause of the accident was an engine stoppage during flight, the specific cause of which could not be determined.
- The aircraft was operating within the restricted area of the height-velocity chart, which significantly contributed to the severity of the impact.