AAIB investigation to Freefly Systems Inc. Alta X 

The UAS, an Alta X, was being operated commercially to provide video footage at the Henley Royal Regatta when a low voltage battery warning occurred in flight at a height of 50 m. As the aircraft was being flown back to the landing site, the aircraft battery voltage was reduced to the point where controlled flight was lost.

It fell, in near free fall, and impacted a boat on the river, causing damage. No persons were injured. The pilot could not recall checking the aircraft’s battery voltage prior to takeoff, and the low voltage battery warning had been changed to trigger at a lower level than that recommended by the manufacturer.