What happened
On December 12, 1978, a Bell 47 G5 helicopter, registration HB-XHW, departed from Basel-Mulhouse airport for a repositioning flight to Bern. The flight was intended to facilitate a 100-hour inspection. Shortly after takeoff, while flying near Neuwiller, France, the aircraft experienced a sudden loss of power. Witnesses observed the helicopter spinning violently on its vertical axis, shedding debris such as plexiglass fragments, before impacting the ground and catching fire. The impact resulted in one fatality, the pilot, and the total destruction of the aircraft.
The investigation
Investigators examined the wreckage and the engine components to determine the cause of the power loss. The investigation focused on the engine's Lycoming powerplant and the pilot's recent flight experience. Analysis of the engine showed no mechanical malfunctions, and the fuel was found to be within standard specifications. However, the investigation noted that the carburetor heat control was found in the 'off' position, and the carburetor temperature gauge was in the orange zone, indicating significant icing. The wreckage also revealed that the engine had stopped prior to the impact, as the fan blades showed no signs of rotation during the crash.
Findings
- The primary cause of the accident was an engine failure caused by carburetor icing.
- The pilot had very limited experience on the Bell 47 G5 model, having flown only six minutes on this specific type prior to the accident.
- The pilot failed to activate the carburetor heat in a timely manner to prevent ice buildup.
- During the engine failure, the pilot's use of the anti-torque pedals caused the aircraft to spin, which prevented the execution of an autorotative landing.
- Meteorological conditions, including a temperature of 7°C and high humidity, were highly conducive to carburetor icing.