Sequence of Events
On Sunday 14 December 2008, a topdressing aircraft departed from Stratford Aerodrome at 0630 hours for a transit flight to a farm airstrip near Tarata. Shortly after becoming airborne, the pilot noticed the engine chip detector warning light on the instrument panel was illuminated and diverted to the company maintenance base at Wanganui aerodrome. An engineer found a light metallic fuzz on the engine magnetic plug, cleaned it, and refitted the plug. The aircraft was released to service with a condition that a further inspection of the mag plug be performed after 10 hours flight time.
The topdressing job, involving 450 tonnes of lime, had commenced on Thursday 11 December 2008 and continued on Friday 12 December. No flying took place on Saturday 13 December due to a local horse-riding event. The aircraft arrived at the farm airstrip at 0940 hours on Sunday and commenced operations to complete the spreading of the lime. At the time of the accident, 423 tonnes of lime had been spread.
The pilot flew several topdressing flights before the first refuel. The loader driver reported that the pilot had difficulty with the lime product not flowing consistently from the hopper during sowing runs. At approximately 1145 hours, the pilot stopped to refuel, giving an estimated fuel load of 300 litres. After two further flights, on the third flight the aircraft became airborne at the end of the airstrip and then descended 55 feet below the airstrip level, where the aft fuselage struck a fence line. A concentration of lime along the take-off path indicated an attempt to jettison the load at the end of the airstrip. Following the fence collision, the aircraft remained airborne for a further 450 metres before impacting the side of a small hill in a slight nose-down attitude. The aircraft came to rest 12 metres to the left of the initial impact point. The accident occurred in daylight at approximately 1155 hours NZDT, at Tarata, elevation 410 feet amsl.
Investigation Findings
The pilot was appropriately licensed, held the appropriate Medical Certificate, and was experienced and fit to carry out aerial topdressing operations. The aircraft had been operating normally from the airstrip up to the time of the accident. The investigation concluded that the aircraft descended after take-off and struck a fence. The collision damaged the elevator control cable system, jamming the elevator control surface. This resulted in the pilot being unable to adequately control the aircraft in pitch, leading to the subsequent ground impact.
The aircraft was loaded with 1900 kg of lime product on the accident flight, exceeding the maximum structural hopper load of 1860 kg. No variation above the maximum structural hopper load is allowed under CAR Part 137. However, the aircraft’s all-up weight at the time of the accident was under the maximum allowed under the overload provisions of CAR Part 137 by 145 kg. The Aircraft Flight Manual does not provide take-off performance data for operation over the maximum certificated take-off weight up to the maximum agricultural weight allowed by CAR Part 137.
A change in wind direction had occurred in the late morning, which may have presented a slight tailwind or possible low-level turbulence, including downdraft conditions, during and after take-off. The windsock was not in the most suitable position to indicate wind conditions to the pilot.
Partial or full load jettisons had taken place on previous flights, indicating difficulty achieving required aircraft performance during or after take-off. On the accident flight, the aircraft was probably overloaded for the prevailing environmental conditions. The reported poor flowing qualities of the lime product may have hampered the pilot’s efforts to jettison the load after take-off. The effectiveness of the jettison may have also been reduced by the downward flight path of the aircraft on leaving the airstrip. It is unlikely that the pilot could comply with CAR Part 137.103 requirement to jettison 80% of the load within five seconds.
The possibility of a pre-existing airframe or engine defect that could have contributed to the accident was eliminated as far as practicable by the investigation. The ELT fitted to the aircraft was no longer an approved type, rendering the aircraft non-airworthy under CARs. The ELT was incapable of being detected by satellite and would not automatically alert rescue services, but this did not hamper rescue efforts.
The accident was not survivable.