What happened
On 21 May 2014, a Bell 206B helicopter, registration ZS-HKF, was conducting a cross-country training flight from Wonderboom Aerodrome toward Newcastle Aerodrome. The aircraft was flying in a loose formation with two other helicopters when, approximately 15 minutes into the flight, the pilot flying noticed a rapid drop in turbine outlet temperature. This was immediately followed by an 'ENGINE OUT' warning light.
As the engine lost power, the helicopter pitched upward and yawed to the left. The flight instructor took control and initiated an autorotational descent toward an open field. During the attempt at a forced landing on uneven terrain, the aircraft's nose pitched forward violently. In an effort to counter this downward pitch, the pilot applied back pressure on the cyclic; however, this movement caused the main rotor blades to strike and sever the tail boom. The helicopter rotated 45 degrees before coming to rest. Despite the substantial damage to the skid gear, tail boom, and rotor blades, there were no injuries to the two pilots or the passenger on board.
The investigation
SACAA AIID investigators examined the engine and the maintenance history of the aircraft. Records showed that just days prior, the engine's compressor module had been removed for cleaning and reinstalled. During testing of the engine in a test cell, investigators discovered that the Pc air filter had been installed in the wrong direction.
Further inspection revealed that the filter element had become detached from its lid due to the reversed airflow. This allowed the element to move freely within the housing, eventually obstructing the airflow to the governor. This restriction limited fuel flow to the combustor, preventing the engine from reaching required power levels and ultimately causing the in-flight stoppage.