What happened
On 29 June 2022, a Freefly Systems Inc. Alta X was being used for commercial filming during the Henley Royal Regatta in Oxfordshire. The aircraft was operating from a pontoon on the River Thames, tasked with capturing footage of boat racing. During its 21st flight of the day, the drone was positioned approximately 250 m up-river when a low voltage battery warning was triggered.
In an attempt to land the aircraft quickly, the pilot directed it back toward the landing pontoon. However, as the drone reached a height of approximately 50 m, the battery voltage depleted to a point where the propulsion system could no longer maintain stability. The aircraft entered a near free-fall, losing all controlled flight. During its descent, the drone struck a private boat, The Celtic Queen, which was carrying six people. The impact caused damage to the boat's cabin roof and handrail, and one of the aircraft's batteries detached and landed on the deck near the passengers. The aircraft subsequently fell into the river and was not recovered. No injuries were reported.
The investigation
The AAIB examined the flight circumstances, the aircraft's configuration, and the pilot's operational procedures. The investigation established that the aircraft was operating in the 'Specific' category, with an authorization allowing it to fly near uninvolved persons under certain distance constraints.
Investigators reviewed the pilot's battery management strategy, noting that while the pilot intended to replace batteries every three flights, the aircraft was actually on its sixth consecutive flight since the last change. Furthermore, the investigation looked into the aircraft's warning settings, finding that the threshold for the low voltage alert had been manually adjusted by the pilot to a lower level than the manufacturer's recommendation.