Aviation safety investigations & reports

Loss of control during taxi, involving RF Designs Mephisto, remotely piloted aircraft Bruhl Airfield, 2 km south-west of Tara, Queensland on 19 June 2020

Investigation number:
Status: Completed
Investigation completed
Phase: Final report: Dissemination Read more information on this investigation phase


Download Final Report
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What happened

In the early afternoon of 19 June 2020, the pilot of an RF Designs Mephisto, remotely piloted aircraft (RPA), was conducting test flights following aircraft maintenance. After completing a successful autonomous test flight, the pilot toggled the automatic mode switch to disengage the aircraft’s automatic mode for taxi back to the hangar.

The pilot then increased the throttle to provide the aircraft with sufficient momentum to taxi. As the aircraft turned towards the pilot, they determined that the aircraft was not responding to commands to reduce the engine thrust. The pilot considered attempting to arrest the aircraft by hand but determined it was moving too quickly and instead toggled the automatic mode switch to regain control of the aircraft and turn it away from bystanders.

The pilot then directed the aircraft across the airfield and it came to rest against the perimeter fence, resulting in minor damage to the aircraft’s skin.

What the ATSB found

The ATSB determined that, following the autonomous flight, the pilot did not correctly disengage the aircraft’s automatic mode. Subsequently, when they increased the throttle to provide the aircraft with momentum to taxi back to the hangar the ’abort landing’ function activated, increasing the throttle to maximum and overriding the pilot’s commands to decrease throttle. The pilot was able to deactivate the ’abort landing’ function by toggling the automatic mode switch.

It was determined that the pilot did not identify visual, audible and tactile cues that indicated the aircraft had not exited the automatic mode prior to increasing the throttle for taxi. The most likely reason for this was that they were experiencing a level of fatigue known to impact performance.

Additionally, the pilot’s controller utilised switches with 3‑positions for 2‑position (on – off) roles, increasing the likelihood of incorrect or incomplete selection. The controller also lacked the means to enable the pilot to immediately shut down the aircraft’s engine.

What has been done as a result

In response to this incident the operator implemented several changes to their systems and procedures. They advised that 3‑position switches on the aircraft controllers, which were being used for 2‑position roles, have been replaced with 2‑position switches. A formalised taxi-in procedure has been introduced that requires personnel to shutdown aircraft on the runway and push them to the hangar by hand. A gated switch was installed on the remote controller that was capable of overriding all other controls, placing the flight controller into manual mode and commanding the throttle to shut down the turbine engine.

For subsequent operations the flight test timeline was increased from 7 to 10 days with no increase in workload. The additional time was to allow for aircraft setup and testing prior to operations commencing and to ensure that all crew members were provided with adequate rest and recovery time during both setup and operations.

Safety message

This incident has 3 key learnings for RPA operators:

  • Fatigue is a risk, particularly in high tempo commercial operations. Even when fatigue management is not mandated, operators should ensure that their fatigue management processes are robust and effective.
  • All controls for RPA’s should be as simple and reliable as possible. If a control leaves room for human error, then it will increase the risk of this error occurring even if procedural controls are in place. Consideration should also be given to a system that allows the remote pilot to shut down the aircraft immediately in the event of an unexpected state or failure.
  • Operators should be prepared for the RPA to do something unexpected and know and frequently practice emergency procedures.
Download Final Report
[Download  PDF: 2.15MB]

The occurrence


Safety analysis


Safety action


Sources and submissions

About the ATSB


The ATSB is investigating an occurrence of control issues during taxi involving a Composite ARF ‘Mephisto’ model UAV at Bruhl Airfield, Tara, Queensland on 19 June 2020

Following the completion of an automated flight, the aircraft was being taxied manually back to the apron. During the taxi, the autopilot’s ‘abort landing’ command was activated and the aircraft accelerated. The pilot re-established manual control of the aircraft and diverted it towards a fence. The aircraft collided with the fence, resulting in minor damage.

As part of the investigation, the ATSB will interview the pilot, obtain and review recorded flight and controller data, and review the operator’s procedures.

A report will be released at the conclusion of the investigation.

Should a critical safety issue be identified during the course of the investigation, the ATSB will immediately notify relevant parties so appropriate action can be taken.

General details
Date: 19 June 2020   Investigation status: Completed  
Time: 1247 EST   Investigation level: Defined - click for an explanation of investigation levels  
Location   (show map): Bruhl Airfield (2 km south west of Tara, Queensland)   Investigation phase: Final report: Dissemination  
State: Queensland   Occurrence type: Loss of control  
Release date: 14 June 2022   Occurrence category: Incident  
Report status: Final   Highest injury level: None  

Aircraft details

Aircraft details
Aircraft model Mephisto  
Aircraft registration N/A  
Serial number HP001  
Operator Remote Piloted Systems Pty Ltd  
Type of operation Aerial Work  
Sector Remotely piloted aircraft  
Damage to aircraft Minor  
Departure point Bruhl Airfield  
Destination Bruhl Airfield  
Last update 14 June 2022