What happened
On 25 March 2019, a DJI Inspire 2 was performing aerial surveillance of a heathland fire at Chobham Common, Surrey. The mission involved streaming live footage to ground-based observers. Following two successful sorties, the pilot performed a 'warm start' by replacing the battery to continue operations. During the third flight, the aircraft reached an altitude of 365 ft and moved approximately 1,63 5 ft away from the take-off and landing site.
As the pilot initiated a return to the landing site, the aircraft experienced a sudden rightward yaw and began a rapid, uncontrolled descent. During the fall, the pilot and a spotter observed an object—believed to be a piece of a propeller blade—detach from the aircraft. A high-pitched squeal was also noted during the descent. To protect bystanders, the crew shouted warnings, prompting a nearby member of the public to seek cover. The aircraft crossed a road and struck the ground on a verge, resulting in the destruction of the UAS.
The investigation
An examination of the wreckage by the operator revealed that while all four propellers were correctly seated on their hubs, the structural integrity of the blades was severely compromised. Of the eight total blades, only two remained intact. The remaining six blades had fractured at or near the hubs. While the investigation did not include a detailed analysis of the fracture surfaces, the operator's findings pointed toward a mechanical failure of the blades, though a malfunction in the speed controller was not entirely dismissed.
Findings
- The primary cause of the loss of control was an inflight propeller blade failure.
- The pilot had not performed a full pre-flight inspection during the battery change, as the 'warm start' procedure did not mandate one.
- Had a physical inspection of the propellers been conducted during the battery swap, a pre-existing crack in a blade might have been identified.
Safety action
- The operator has updated its 'warm start' procedures to include mandatory physical inspections of the propellers before subsequent flights.
- The operator has issued instructions to all pilots prohibiting the overflying of people.