Man injured by fallen drone propeller while mowing lawn, investigators say

A man was injured after a drone propeller fell on him in Dublin, according to a report from air accident investigators.

The incident occurred during an urban flight by the Manna unmanned drone delivery company in July 2022.

The Air Accident Investigation Unit released a report on the incident on Friday.

It said a propeller blade became separated from the drone during the flight, causing severe vibrations and the subsequent failure of an electric motor.

This triggered the on-board flight termination system and emergency parachute deployment. The drone struck the ground with minor damage.

Meanwhile, the propeller blade that had separated struck a man on the ground.

The man told the investigation that he was mowing the lawn in his back garden when he was struck by what he believed to be part of a propeller from a drone.

He stated that he did not notice anything unusual before being struck due to the noise emitted from his lawnmower. He said that he sustained a small cut to his head but did not require stitches nor hospital attention.

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The investigation determined that the probable cause of the accident was a fatigue fracture of a bolt securing the propeller blade, which caused the blade to separate from the drone.

The drone did not have an airworthiness certification, but was not required to have one.

The remote pilot had not been issued a Practical Assessment Completion Certificate until after the accident, the report said.

The drone impacted the ground in a public park and sustained some damage. The AAIU was not notified of the accident as required.

The propeller manufacturer stated that the polymer propeller as used on the drone should not be used in a coaxial configuration. Manna subsequently redesigned the propeller hub.

Manna has also committed to changing from the current coaxial configuration to a new design consisting of a single propeller mounted on each arm.

Manna said it appreciated the AAIU report, saying the incident was “a controlled landing” and not a crash.

The company’s website says drone deliveries are a “safer” alternative to delivery drivers, as it results in reduced vehicles on the roads and fewer crashes.

In a statement, it said: “The report emphasises that this incident was a unique, singular occurrence. We are pleased to report that since the event over two years ago, we have had no issues with propeller integrity.

“Following the incident, our company swiftly implemented design and procedural changes to further bolster the safety and reliability of our operations.”

It added that the aircraft’s Flight Termination System activated as intended, deploying the emergency parachute to ensure a safe descent after a propeller malfunction. This system is designed specifically to prioritise the safety of individuals on the ground and to reduce any potential risk during an unexpected event.

“Our priority remains the safe and reliable delivery of goods to our customers, and we continue to work in close collaboration with the Irish Aviation Authority (IAA) to meet all regulatory standards.” – PA