What Happened
On 25 January 2024 at 0640 local time, a Raytheon Aircraft Company C90A aircraft, registered VH-JEO and operated by Goldfields Air Services, departed Kalgoorlie-Boulder Airport, Western Australia, on a commercial passenger transport flight to Warburton Airport. The aircraft carried one pilot and two passengers. Approximately half an hour into the flight, while operating in instrument meteorological conditions (IMC), an avionics failure caused the aircraft to commence an uncommanded turn to the right. The pilot disengaged the autopilot and manually returned the aircraft to the correct heading. During this manoeuvring, altitude variations between −400 ft and +900 ft were recorded on ADS-B tracking services. The monitoring air traffic controller observed the deviations and queried the pilot's intentions multiple times. The combination of manual flight in IMC, troubleshooting, and controller interactions resulted in high workload for the pilot. The pilot decided to return to Kalgoorlie, and the aircraft landed around 0800 local time.
ATSB Findings
The Australian Transport Safety Bureau (ATSB) identified that the left remote gyroscope failed, producing erroneous indications on the horizontal situation indicator (HSI). With the autopilot engaged in heading mode, this caused a sustained, uncommanded right turn as the autopilot attempted to follow the drifting heading bug. The pilot initially disengaged the autopilot and manually corrected the heading. However, contrary to the guidance in the pilot operating handbook (POH), the pilot later re-engaged the autopilot in heading mode to reduce workload. This action led to the resumption of the uncommanded turn, requiring constant adjustments to the heading bug and increasing workload. The ATSB noted that disengaging the autopilot and using an alternate compass system would have eliminated the turn. The pilot did not make a PAN PAN broadcast to air traffic control, likely due to focused attention on the malfunction, reducing the opportunity for controller assistance.
Safety Actions
Following the incident, the operator issued a notice to aircrew reminding pilots to disengage the autopilot and hand-fly the aircraft when failure modes are indicated on the autopilot annunciator. Additionally, the operator added training exercises related to HSI and artificial horizon instrument failures during line-oriented flight training for all pilots.
Summary
This incident involved a single-pilot commercial flight in IMC where a gyroscope failure led to an uncommanded turn. The pilot's decision to re-engage the autopilot contrary to POH guidance increased workload and control difficulties. The absence of a distress broadcast limited ATC's ability to assist. No injuries or fatalities were reported.