Delivery drone propeller injures bystander

A really great example of an incident report write up, well done the Irish Air Accident Investigation Branch. I will put in the summary and leave you to read the .PDF below.

This History of Flight is based primarily on a technical report provided by the Operator, interviews with the RP, and witness accounts. The UA was tasked with conducting an urban delivery to an address in the Tankardstown area of Balbriggan, Co. Dublin. At 16:49 hrs, the UA departed from its base of operations, located on top of a multistory carpark at the Millfield Shopping Centre in Balbriggan.

The UA ascended to a height of 71 metres (m) and proceeded on its pre-programmed route towards its drop point. Whilst on a north-easterly track and 52 seconds into its flight, a vibration consistent with a propulsion unit imbalance was registered by the onboard software, and a propeller blade driven by the upper rear-right electric motor separated from the UA.

Following separation of the propeller blade, the UA pitched up and rolled to the right. To compensate for this uncommanded pitch and roll, and in an attempt to maintain stable flight, the UA automatically reduced thrust on the electric motors located on the front left arm and commanded an increase in thrust from the motors on the right rear arm. The UA recovered attitude control and maintained altitude for the next 20 seconds.

Due to vibration, the UA’s master Flight Control Unit (FCU) was unable to accurately compute the UA’s attitude and altitude, and automatic switching to a backup FCU occurred.

This was followed by a drop in altitude of approximately 2.5 m. To compensate for this height loss, increased thrust was commanded from the remaining propellers followed by a short climb segment. Approximately five seconds after the FCU switching, the lower rear right electric motor failed completely due to the effects of vibration, with the remaining (upper) motor on the rear-right arm driving a single propeller blade.

The UA’s automatic Smart Return To Land (SRTL) feature activated in an attempt to automatically return the UA to its operating base. Due to the yaw demands commanded by the SRTL, the UA descended with a speed of 3 m per second (m/s) and the onboard monitoring system detected increasing errors in both pitch and roll axes. The UA continued to descend with the rate of descent increasing to a maximum of 8.5 m/s and all remaining motors were automatically stopped. The Flight Termination System (FTS) activated and the onboard parachute was ejected from its tube. As the UA descended through approximately 20 m, the rate of descent decreased to 4.9 m/s before the UA impacted with grassy terrain and came to rest, inverted, near a public footpath. The Operator initiated their Emergency Response Plan (ERP) and its personnel travelled to the accident site.

The UA was video recorded in situ and subsequently recovered to the Operator’s base.

Injuries to Persons

One individual informed 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 prior to being struck due to the noise emitted from his lawn mower. He said that he sustained a small cut to his head but did not require either stitches or hospitalisation. This individual provided the Investigation with an image of what he states struck him in the head.

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