At the start of the take-off run, one propeller blade separated from the hub. The resulting propeller imbalance caused damage to the engine and airframe. The fracture was caused by the growth of a fatigue crack from the second blade retention thread. No material abnormalities or stress concentrators contributed to fatigue initiation. It was estimated that fatigue growth had occurred over a period of approximately 2100 take-off/landing cycles. The Civil Aviation Authority subsequently amended the Airworthiness Directives relating to this type of McCauley propeller, when fitted to agricultural aircraft. These amendments include a reduction in hours between overhauls, and more detailed inspections of the threaded section of the blades.