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This report summarizes the detailed and protracted investigation into the cause of the engine failure that resulted in ZK-NSR landing short of runway 8 at Whenuapai. The investigation was carried out over a period of about three months and was coupled with checks, tests and procedures aimed at ensuring that the probability of future engine failures was minimal. Checks included cylinder compression, valve seating and timing, ignition timing, fuel supply and the electrical system and engine instruments. Also included were static thrust measurements, fuel pressure measurements, cowl pressure measurements and engine temperature.

The exhaust gas analysis showed that the engine runs rich with the cowls off. The engine was originally tuned in accordance with the supplier's instructions with the cowl off and as a result, the engine was probably lean in flight with the cowls on. The engine was possibly further leaned by fuel starvation by an aglomeration of sub-40 micron particles in the low speed jet. It is also possible that weak spark resulting from a low battery may have contributed to the engine stoppage.

Action taken included the readjustment of the tachometer, modification of the cowls and baffling, fitting a 2-micron filter downstream of the standard 40-micron filter, and tuning the engine with an infrared exhaust gas analyzer.

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