Incident Overview
On 28 February 2023, at approximately 2328Z, a remotely piloted aircraft (RPA) DJI Mavic 2 Enterprise, registration ZT-YPH, was conducting an aerial survey for Transnet railway patrol near Paulpietersburg (Dumbe), KwaZulu-Natal Province, South Africa. The flight was operated under Part 101 of the Civil Aviation Regulations (CAR) 2011 as amended, beyond visual line of sight (BVLOS) rules. Visual meteorological conditions (VMC) by night prevailed, with wind from the southwest at 4 knots gusting 9 knots, clear visibility, and temperature 21°C. A caution was issued that the weather conditions were “not good to fly.”
Flight Sequence
The pilot, holding a valid Remote Pilot Licence (RPL) with multirotor ratings, commenced operations at 2130Z after pre-flight checks. Four successful survey flights of approximately 18 minutes each were completed. On the fifth flight, launched at approximately 2315Z with 99% battery power, the RPA climbed to about 115 metres above ground level (AGL). After reaching the end of the survey area (turning point), the pilot began the return flight for a full-stop landing at the launch site. At about 2328Z, the remote controller unit display screen blacked out. The pilot immediately activated the return-to-home (RTH) function, but the screen remained blank. The pilot then identified the RPA by its flashing navigational lights as it descended toward the ground.
Post-Incident Search and Recovery
The pilot searched for the RPA at its last known position but could not locate it. The search continued the next day without success. Thirty days after the incident (30 March 2023), Transnet security personnel found the RPA at a different location from the initial search area. The RPA was not damaged.
Findings
The operator’s post-incident investigation revealed that the remote controller unit’s battery depleted during operation, causing the screen to black out and the remote control signal to be lost. According to the RPA user manual, the remote controller battery should be fully charged before each flight. The manual also states that a failsafe RTH automatically activates after the remote control signal is lost for more than two seconds, causing the RPA to retrace its original flight route to the home point.
The pilot held a valid RPL issued on 10 November 2022, with an expiry date of 30 June 2024, and a Class 3 medical certificate valid until 31 December 2026. The operator held a valid Remotely Piloted Aircraft Operating Certificate (ROC) and Letter of Approval (ROA). The RPA had a Certificate of Registration issued on 24 August 2022, and last periodic maintenance was conducted on 4 February 2023 at 106.17 hours.
Probable Cause
The remote controller unit’s battery depletion during operation led to the controller screen blackout and loss of remote control signal.