What happened
On 18 January 2018, an Aery/on Skyranger R60 (registration SR9112798) was being operated for aerial work in Brixton, London. The flight, conducted at night by a pilot and an observer, involved a camera-equipped unmanned aircraft (UA) flying with CAA authorization. After taking off and reaching an altitude of approximately 50m, the aircraft encountered wind speeds that exceeded its design capabilities. The ground control unit issued a warning regarding strong winds, presenting the pilot with options to either ignore the warning or initiate a 'Home and Land' procedure. The pilot did not select either option.
As the aircraft struggled to maintain its position, it drifted behind a five-storey building, causing a loss of radio line-of-sight and a subsequent loss of the control signal. During this period, a software error was triggered. Instead of attempting to return to the takeoff point, the aircraft's software commanded an immediate descent. The UA eventually struck the top of a tree at roughly 15m altitude before falling to the ground, resulting in the destruction of the unmanned aircraft.
The investigation
Investigators examined flight logs from the ground control unit and recovered video footage. While the internal flight data on the aircraft was destroyed upon impact, the recovered logs confirmed the sequence of altitude and direction changes. The investigation also focused on the software version installed on the system. It was established that the aircraft was running version 3.6.11, which contained a known error. A fix had been developed by the manufacturer in June 2017, but it had not been implemented on this specific unit.
Meteorological data from nearby airports, including London City and Heathrow, were reviewed. While the pilot had relied on weather applications and forecasts that suggested manageable conditions, actual wind speeds at the time of the incident were significantly higher than the aircraft's operational limits.
Findings
- The aircraft encountered sustained winds exceeding the manufacturer's stated maximum of 65 km/hr.
- The pilot relied on forecast weather data rather than actual, real-time meteorological reports from nearby airfields.
- A software error caused the aircraft to attempt an immediate landing instead of returning to its home position when the 'return home' mode was triggered.
- The loss of the radio link was likely caused by the aircraft drifting behind a building, breaking the line-of-sight between the ground station and the UA.
- The operator was unaware that a software update was available to rectify the known landing error.
Safety action
Following the accident, the operator implemented several safety improvements, including:
- Integrating software version checks and updates into standard maintenance protocols.
- Implementing a mentoring scheme to support less experienced crew members.
- Mandating the use of actual weather reports rather than just forecasts for flight planning.
- Establishing stricter wind speed limits for operations to provide a safety margin.