On touchdown following a superphosphate spreading operation, the pilot heard a loud cracking noise from the left side of the aircraft. Shortly afterwards the left mainwheel detached, the aircraft swung sharply and tipped onto its nose, before coming to rest in an upright attitude. The left mainwheel axle was found to have fractured. The left axle had been in service for 7452 flight hours, and was estimated to have been involved in about 70,000 landings. The failure was determined to have initiated from fatigue cracking, which had propagated through about 60 percent of the axle diameter before the axle ultimately failed from overload forces.