Shortly after lift-off, both propeller blades separated from the aircraft, which then touched down and subsequently overturned. One of the propeller blades was located 80 metres to the left of the strip and the other, with hub and constant speed unit attached, was located 40 metres to the right of the strip. The propeller hub contained a fracture which was caused by the propagation of a fatigue crack originating at the root of the blade retention thread. The engine had been fitted with two fifth order crankshaft damper weights. This was contrary to the manufacturer's requirement, which was for one fifth order and one sixth order counterweight to be fitted. It is considered likely that fitment of the incorrect counterweights initiated and contributed to the propagation of the fatigue crack.