The nose gear leg failed whilst the aircraft was taxiing. Detailed examination of the failed leg concluded the failure was due to a fatigue fracture. Because of previous similar failures, this part number nose gear leg was subject to an Airworthiness Directive that required regular inspection for cracks. This inspection had been completed 33 flying hours earlier, with no defect found. Since then the aircraft had been used for basic training, which involved a large number of takeoffs and landings from grass runways.