What happened
On 24 September 2015, a private AS350B2 helicopter, registration ZS-OCB, was conducting a flight from Grand Central Aerodrome toward the north of Pelindaba. Approximately 20 minutes into the flight, the pilot activated the aircraft's air-conditioning unit. Shortly thereafter, smoke began entering the cabin through the ventilation vents.
In response to the smoke, the pilot initiated an autorotational flight to perform a precautionary landing in an open field. As the aircraft descended to approximately 200 feet above ground level, the volume of smoke increased significantly, severely impairing the pilot's ability to see outside the cockpit. During the final stages of the landing, the aircraft experienced a heavy impact, with the tail stinger striking the ground first. This impact caused the aft tail boom to twist and resulted in a tail rotor blade separating from the hub assembly. There were no injuries to the two occupants.
The investigation
SACAA AIID investigators examined the wreckage and the flight sequence to determine the origin of the smoke. The investigation confirmed that the engine and flight control systems were fully functional and had not failed. Investigators located a melted drive belt on the transmission platform, which was identified as the source of the smoke. The melting of the air-con drive belt was the direct cause of the smoke entering the cabin.
Findings
- The primary cause of the hard landing was obscured vision caused by the smoke filling the cabin.
- The smoke originated from the melting of the air-conditioning unit drive belt.
- The pilot failed to identify the specific source of the smoke or any underlying system failures before initiating the emergency landing.
- The pilot did not switch off the air-conditioning unit, which would have stopped the smoke flow.
- The pilot did not consult the helicopter's flight manual regarding emergency procedures for smoke in the cabin.
- The underlying reason why the drive belt melted could not be determined.
Safety action
Following the investigation, a safety message was issued emphasizing that pilots must strictly adhere to manufacturer-issued emergency procedures and regulatory instructions to prevent similar incidents.