Tailwheel Detachment on a Maule Air M-7-235C at Otone Temporary Airfield (JA30HT)

Incident Overview and Investigation Scope On December 4, 2015, a privately owned Maule Air M-7-235C, registered as JA30HT, experienced a serious incident at Otone Temporary Airfield in Kawachi Town, Ibaraki Prefecture, Japan. The aircraft, which had just completed a flight for an airworthiness inspection, damaged its tailwheel while taxiing to the apron. The Japan Transport Safety Board (JSTB) investigated the event to prevent future occurrences, with participation from an accredited representative of the United States as the state of design and manufacture. ## Flight History and Damage Assessment The aircraft took off at 11:10 with the captain and two passengers on board, landing at 11:30. During taxiing at approximately five knots, the captain noticed an unusual sensation and stopped the aircraft. Upon inspection, the tailwheel was found to have detached and fallen after the connecting bolt fractured at the bolt head. The incident resulted in no injuries to persons, and the aircraft sustained slight damage. ## Maintenance History and Technical Findings The tailwheel, a Scott Aviation Corporation model 3200-00, was installed in 1999. Maintenance records indicated that in 2014, a shaved dent was observed around the bolt hole, and the bolt was replaced, but the washers and nut were not. In 2015, similar wear was noted, but the parts were deemed serviceable. The JSTB found that the bolt had been subjected to excessive grip length, with three washers totaling more than the recommended thickness. ## Probable Cause and Analysis The JSTB determined that the tailwheel detached because the connecting bolt fractured due to fatigue originating from bolt loosening. This loosening was likely caused by vibration during taxiing and impact loads at landing, exacerbated by the improper use of washers that exceeded standard thickness limits. The investigation highlighted the lack of specific maintenance manuals for the tailwheel parts, which contributed to the use of non-standard components.