A man mowing a lawn in his back garden suffered a minor injury after a propeller blade fell off a drone that was delivering a package to a customer in north Dublin two years ago.
A report by the Air Accident Investigation Unit (AAIU) has revealed details of the incident involving a GEN 3.8 unmanned aircraft at Tankardstown, Balbriggan, Co Dublin on 14 July 2022.
An investigation found one of the eight propeller blades separated from the drone during an urban delivery flight at around 4.51pm which resulted in severe vibrations to the drone.
It led to the failure of the aircraft’s electric motor which in turn triggered the onboard flight termination system and the deployment of an emergency parachute.
One eyewitness, who was struck on the shoulder by a fragment of a propeller blade, told the AAIU that the drone “wobbled for a second and then bits and pieces started showering down.”
The drone, which suffered minor damage on landing, came to rest upside down near a public footpath.
A man cutting grass in his back garden informed the AAIU that he was struck by what he believed was part of a propeller from a drone.
He told investigators he did not notice anything unusual prior to being hit due to the noise from his lawn mower.
The injured male sustained a small cut to his head but did not require stitches or hospitalisation.
Although the report did not identify the operator of the drone, Manna – a company operating a drone delivery service – had previously confirmed that the incident involved its equipment.
The operator was delivering small packages to customers in the Balbriggan area who order goods online through an app.
The report said the flight path of the drone from its operating base on the top of a multi-storey car park at the Millfield Shopping Centre in Balbriggan avoided assemblies of people and overflight of sensitive areas such as schools.
A member of the operator’s ground team was first on the scene and disconnected the battery to silence the onboard warning siren on the drone that had been activated.
The remote pilot said the nature of the damage to the drone suggested it did not impact the ground with excessive force.
All flight operations by the company were temporarily ceased until a root cause for the accident could be established.
The AAIU noted the remote pilot had received training from a training body recognised by the Irish Aviation Authority as well as completing a practical skill assessment, although the associated certificate was not issued until after the accident.
The operator told investigators that a new bolt tightening procedure for propellers had been introduced into its Balbriggan operation some weeks before the incident and it believed staff at the location tended to overtighten bolts.
It informed the AAIU that the bolt tightening procedure has been revised since the incident and all bolts in operation at the time have been removed from service and destroyed.
The company said it had also redesigned the propeller hub with a “failsafe” mechanism which will prevent a similar incident in future in the event of a bolt failure.
The AAIU said the operator should ensure that critical components of the drone should be used “in accordance with the manufacturer’s instructions,” although investigators acknowledged the coaxial configuration was not a contributory factor in the incident.
They noted that the operator had conducted an analysis of a number of events involving its drones which concluded that any failure with rotors was due to human error rather than a system failure.
The AAIU also confirmed the company was operating the flight under a certificate issued by the IAA and had conducted it in good visibility and within specified wind limitations.
The investigation concluded that the probable cause of the accident was a fatigue fracture of a bolt securing the propeller blade which caused it to separate from the drone.
The AAIU made no safety recommendations following the incident.
