The Piper Chieftain aircraft was on a charter flight from Port Augusta to Olympic Dam mine site. This was a daily return operation ferrying mine personnel who reside in Port Augusta and commute to the site. The flight was conducted in accordance with the Instrument Flight Rules (IFR) in Visual Meteorological Conditions (VMC) and arrived at Olympic Dam just before 0700 hrs (CST) on the day of the accident. After an uneventful flight, the pilot manoeuvred the aircraft to join the circuit and proceeded to land on runway 24.
Shortly after landing, the nose landing gear collapsed, followed soon after by the left main landing gear. The aircraft then departed the runway to the left tracking 220 degrees approximately 430m from the threshold. The ground slide continued for another 70m with the aircraft coming to rest facing 090 degrees. The pilot and passengers evacuated the aircraft without injury. The pilot later stated that the cockpit indications showed that the landing gear was down and locked prior to landing.
Maintenance investigation could find no mechanical fault present that could have prevented the landing gear extending to the down and locked position. All functional tests carried out proved the landing gear retraction system to be without fault at the time of the accident. It was noted during the rebuild, that the landing gear throttle warning micro switches were not adjusted correctly. If a landing had been attempted with the landing gear not fully extended, this micro switch adjustment would have prevented the warning horn activating.
The landing gear collapse after touch down is consistent with the landing gear not being in the fully down and locked position on touch down. When the landing gear accepted the weight of the aircraft after touch down, the effect was to collapse the unlocked nose and left main gear legs. The probable reason for the landing gear not being down and locked was that the extension cycle was interrupted at some point which prevented the landing gear from completing its travel to the fully down and locked position.
This interruption is most likely to have been caused by the premature return to neutral of the landing gear selector lever from the down selected position. The reason the lever prematurely returned to neutral could not be positively determined. The landing gear throttle warning micro switch adjustment would have inhibited the activation of the landing gear unsafe horn thus preventing an additional and timely warning being provided to the pilot in command.