Introduction
On the morning of Sunday 23 December 2001, a pilot was engaged in spreading superphosphate on a property near Otonga. After completing that job, the operation moved to a property east of Whangarei to sow urea on a maize crop. That job finished at about 1130 hours, and the pilot and loader driver decided to have tea and plan the next task. Two options were available; the wind was unsuitable for operations from one airstrip, so they chose to complete a job at Paiaka involving spreading approximately 112 tonnes of lime. This job had been delayed since 13 December 2001 due to wind.
Sequence of Events
The loader driver arrived at Paiaka at about 1300 hours and found the pilot already landed, removing the cover from the fertiliser bin holding the lime. Water had seeped under the cover edges, making the lime damp along the bin walls. The truck driver who had delivered the lime earlier in the week had also noted moisture in the lime around the bin edges. Work commenced at about 1320 hours, and the loader driver expected the pilot to stop for fuel between 1445 and 1500 hours.
After approximately 13 loads, the loader driver was using the moisture-affected lime. He took bucket loads from the sides and mixed them with the lime in the middle to improve flow. At about 1425, the pilot signalled for a refuel on the next landing, earlier than expected. The loader driver assumed this was also to check for lime buildup around the hopper bottom. During the 10 weeks they had operated the aircraft, they had occasionally needed to clean fertiliser from the hopper door area, especially when the fertiliser was damp. On one occasion, they had to remove part of a previous load that had “hung up” inside the hopper.
As the loader driver prepared for refuelling, he heard the aircraft operating at what sounded like full power and saw the pilot manoeuvre in an apparent attempt to dislodge the load. He observed a small puff of lime discharge as the aircraft “bunted”. The aircraft then disappeared behind intervening terrain into a valley about 1,500 metres from the sowing area. The loader driver did not see the aircraft again but heard a muffled explosion and saw smoke on the skyline. He called for emergency assistance. The accident occurred in daylight at approximately 1430 hours NZDT at Paiaka, elevation 720 feet.
Investigation Findings
The investigation concluded that the pilot was appropriately licensed, rated, and fit for the flights undertaken. The aircraft had a valid Airworthiness Certificate and had been maintained in accordance with current requirements. The possibility of a pre-existing defect with the aircraft or engine that could have contributed to the accident was eliminated as far as practicable. The pilot was aware that water had affected the lime he was using.
Probable Cause
The pilot encountered a “hung load” of lime, probably resulting from the damp product bridging over the hopper doors, and despite bunting manoeuvres, he was unable to discharge the hopper contents. The aircraft entered a valley system from which there was no means of escape, either by climbing or by carrying out a reversal turn.