procedure in the aircraft. New Zealand’s type rating requirements allow latitude
for demonstrating “knowledge” of procedures that can’t be safely demonstrated in the aircraft, but the pilot’s response to the written exam’s question about the “ECU FAIL
” warning made no mention of switching to manual mode or using the twist throttle. It was marked incorrect but never revised. The instructor subsequently signed him off as competent in FADEC/ECU emergency proce- dures on the required Civil Aviation Authority form.
The Investigation The ECU and HMU were examined by their respective manufacturers. Downloaded data showed that the pri- mary ECU channel shut down 17 minutes into the flight. Eight minutes later, the reversionary governor defaulted to fixed fuel-flow mode. The FADEC switch remained in the AUTO position, and the helicopter touched down 68 seconds later. The ECU had also recorded a “step count failure” on an earlier flight that transferred control to the reversionary governor without being noticed by the pilot. Post-accident testing failed to replicate any of these faults.
While much of the damage might have been avoided had the pilot shut down the engine after the first bounce using the twist grip or fuel-cutoff valve, the Transport Accident Investigation Commission (TAIC) noted that the “severe vibration created by the imbalanced rotor sys- tem” likely impeded his response. The TAIC also noted that none of the occupants wore helmets, likely contributing to the severity of the head injuries sustained. The operator subsequently adopted a
formal policy requiring its pilots to wear helmets on all flights, and on May 27, 2021, the TAIC asked the director of civil aviation to “promote education awareness of the benefits of … occupants wearing appropriate helmets when practicable.”
The Takeaway The belief that operating by manual throttle control posed an undue risk of overspeed was apparently preva- lent among New Zealand’s relatively small number of MD 600N pilots, as was incomplete understanding of the architecture of the FADEC system. (Two MD 600N pilots interviewed by the TAIC “were unaware of the existence of the reversionary governor.”) They shared a reluctance not just to practice using the twist-grip throt- tle but even to using it in a true emergency. The manufacturer advised the TAIC that it has estab- lished a procedure for training pilots in the use of the manual mode. However, the company regards the pro- cedure as “proprietary information … not available out- side the manufacturer’s own training organization.” This description doesn’t make clear whether the man-
ufacturer’s procedure is performed in the aircraft or via simulation using specialized equipment. If the latter, this might justify the added expense of factory training, even on another continent. If the former, however, there’s a strong argument that the company’s long-term benefit in fostering effective emergency-procedures training among everyone flying its aircraft would outweigh any loss of training revenue. Practice doesn’t automatically make perfect, but it usually beats ignorance.
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DECEMBER 2021 ROTOR 63
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