TAIC PHOTO
manager of Ngamatea Station, died the following day. The pilot survived but couldn’t be interviewed for two months, then had no memory of the accident flight. The rear-seat passenger, another company pilot not rated for the MD 600N, did recall the flight.
normal operating range. Redundancy against engine shutdown is provided by
four distinct operating modes. In full FADEC, the ECU’s primary control channel monitors two separate mea- sures of fuel flow transmitted from the HMU. If they dif- fer by more than a specified threshold, the primary channel flags a “step count failure” and transfers control to a reversionary governor, which compares measure- ments of the rate of change in engine speed from two different sensors and illuminates three amber lights on the panel warning of degraded FADEC function. If the difference between those inputs exceeds the
specified threshold, the reversionary governor also records a fault and freezes the step motor in its current position, placing the engine in fixed fuel-flow mode. Until the pilot disengages FADEC using the switch on the col- lective, power output remains constant regardless of flight control inputs. Main rotor rpm will decrease when the collective is raised and increase when it’s lowered. The red “ECU FAIL
” warning on the panel and an accom- The wrecked
fuselage of ZK-ILD at the accident site.
The Aircraft The MD 600N is an eight-seat single-engine helicopter with a fully articulated six-blade main rotor system. It’s powered by a Rolls-Royce 250-C47M turboshaft engine rated for 600 shaft horsepower governed by full-authority digital engine control (FADEC) with manual backup. Anti- torque control is provided by the NOTAR (no tail rotor) system in place of a conventional tail rotor. ZK-ILD was manufactured in 2000 and imported to
New Zealand in March 2018, just three months before the flight in question. At the time, it was one of only two MD 600Ns in the entire country. While this model is nor- mally flown from the left side, some, including ZK-ILD, have been modified to allow single-pilot operation from the right front seat by removing the left cyclic and ped- als. Scheduled airframe and engine maintenance were completed on Mar. 29. The MD 600N’s FADEC system uses a hydromechan- ical unit (HMU) to provide and meter fuel flow to the engine, adjusted by an electronic control unit (ECU) in response to both internal engine status and flight control inputs. Separate wiring harnesses connect the ECU to the engine and airframe sensors. In normal operation, the system controls both power output and main rotor speed without need for direct intervention by the pilot. Signals from the ECU to an electric step motor in the HMU adjust fuel flow to meet power demands while maintaining main rotor rpm within
62 ROTOR DECEMBER 2021
panying audible warning advise the pilot that the FADEC system is now entirely inoperative. The appropriate response, as detailed in the “Emergency Procedures” section of the Rotorcraft Flight Manual, is for the pilot to attempt to reset the ECU by briefly switching the FADEC control on the collective from AUTO to MANUAL. If it doesn’t reset in two attempts, the pilot is to set it to MANUAL and, using the collective’s twist-grip throttle, reduce power to prevent an overspeed. A separate mechanical linkage connects the twist grip to the HMU’s fuel metering valve, allowing the pilot to modulate engine and rotor rpm until a safe precautionary landing can be made.
The Pilot The 45-year-old commercial pilot began training for his MD 600N type rating on Apr. 13, 2018. He was the oper- ator’s chief executive and senior pilot, with more than 9,600 hours of helicopter experience, some in models powered by non-FADEC versions of the RR-250 engine. He obtained his type rating after 2.3 hours of dual instruction and another 2.2 supervised by a 7,000-hour Category D instructor with about 250 hours in make and model. By the day of the accident, the pilot had logged 45 hours in ZK-ILD. Both the pilot and instructor confirmed that they had
never practiced using manual throttle control in flight due to the perceived risk of overspeed. Moreover, the instructor recalled having discussed this point during his own type rating training in 2003 with a Category A instructor who’d advised against practicing the
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