An ATSB investigation into the fatal crash of an Ayres Thrush on crop spraying operations has revealed no causes.
VH-JAY crashed near Hyden, WA, in October 2013 after a loss of control that resulted in it crashing into the ground inverted.
The ATSB investigation found that the aircraft was using an unapproved fuel mixture in the turbo-prop engine, and that the aircraft was being operated outside its centre-of-gravity limits and nearly 1133 kg over maximum weight.
However, the ATSB was unable to state definitely that either of these factors contributed to the accident.
The fuel mixture being used was a 70/30 blend of diesel and avgas with an additive. This type of fuel is not approved for the TPE331 engine fitted to VH-JAY. However, the investigation showed the engine was delivering significant power at the time of impact, ruling out engine failure due to the fuel.
Although the aircraft was over its maximum take-off weight, calculations showed the Thrush should still have had margin over the stall speed. Also, several of the type were operating over the MTOW under a CASA exemption that has been withdrawn. According to the ATSB, there have been no accidents as a result of operating Thrush aircraft over MTOW.
In the report's Safety Message, the ATSB warns pilots about both factors, even though the crash can be attributed to neither.
"Operators and pilots are reminded of the dangers of operating aircraft engines on an unapproved fuel mix as this increases the likelihood of engine damage which could affect the safety of operations. Pilots and operators are also reminded of the need to adhere to an aircraft’s maximum take-off weight to ensure the on-going safety of the aircraft and operations."
The full report is available on the ATSB website.