Overview
The accident occurred during the first load of the day for an aircraft carrying superphosphate fertilizer. The aircraft had almost full fuel at takeoff. Although the exact amount of superphosphate loaded could not be determined, the aircraft's weight likely exceeded both the performance-limited maximum takeoff weight for the strip and the documented maximum takeoff weight. This likely degraded takeoff performance significantly, contributing to the aircraft's inability to clear a stand of trees downslope of the lift-off point.
Engine and Performance Analysis
A tachometer slap mark and audio spectrogram analysis of a video recording indicated that the engine power during takeoff may have been slightly lower than normal. No obvious defects were identified with the engine, and the propeller was rotating under power at impact. The relative humidity at takeoff could not be established, but possible factors affecting engine performance included the volume of water in the air, carburettor ice, or the carburettor heat selector being inadvertently left on during takeoff. However, there was insufficient evidence to determine if any of these events occurred.
Tree Strike and Safety Margins
The pilot had conducted takeoffs from the Seaview runway strip in previous years, but the increased height of trees at the northern end had reduced safety margins. The aircraft struck the trees about 16 feet from the top. Even without an estimated 3–10 feet of extra tree growth, the investigation concluded that there would not have been sufficient clearance for a safe takeoff.
Takeoff Strip Selection
The investigation was unable to determine why the pilot chose to prepare and use a strip oriented directly toward the trees when an alternative takeoff option was available.
Load Jettison Attempt
A limited number of superphosphate pellets were found scattered between the takeoff point and the impact location, indicating that the pilot likely attempted to jettison the hopper contents around the time of becoming airborne. However, the effect of this jettison on aircraft performance was probably insufficient to clear the trees, as the aircraft would have needed to gain about 16 feet in 2 seconds with some load still on board.
Conclusion
The weight excess, possible engine power reduction, tree height, and unsuccessful jettison combined to prevent the aircraft from clearing the trees.