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.