What happened
On 23 July 2010, a Cessna C188B, registration ZS-KDX, was conducting a local flight near Vivo, South Africa. While the aircraft was in straight and level flight, a propeller blade detached from the propeller hub. The sudden imbalance caused intense vibrations, which resulted in extensive damage to the engine. The pilot reacted by switching off the magnetos to stop the engine and subsequently executed a successful forced landing at the destination. The pilot, who was the sole occupant, escaped the incident without any injuries.
The investigation
SACAA AIID investigators examined the wreckage and the aircraft's maintenance history. While the aircraft's logbooks indicated that maintenance was up to date, an inspection of the blade root revealed that a crack had originated on the outside of the root and progressed inward until the final structural failure occurred.
During the inquiry, investigators spoke with various Approved Maintenance Organisations (AMOs). These representatives verbally noted an industry practice where certain tasks required during midlife propeller inspections are omitted to reduce costs for aircraft owners. Specifically, the investigation found that several tasks outlined in the McCauley maintenance manual—which involve the removal of ferrules—were likely not performed.
Findings
- The primary cause of the incident was the separation of a propeller blade from the hub during flight.
- The engine suffered significant damage due to the severe vibrations caused by the resulting propeller imbalance.
- Although official records suggested the propeller was maintained correctly, investigators concluded that the propeller was likely not maintained in strict accordance with the manufacturer's specific requirements.
- Weather conditions were clear and did not contribute to the event.
Safety action
To improve aviation safety, it is recommended that the Director for Civil Aviation ensures all propeller overhaul facilities strictly adhere to the midlife inspection protocols as stipulated by the propeller manufacturer.