What happened
On 4 June 2023, an MNA GEN 3.8 unmanned aircraft was conducting a routine urban delivery flight in Balbriggan, Co. Dublin. The mission involved delivering a small package to a customer's address using a thread-based lowering system. During the descent to the target height of 14 meters, the aircraft's propellers struck the side of a nearby apartment building, which stood approximately 12.99 meters tall.
Following the impact, the aircraft's control system detected a loss of control and triggered the flight termination protocol. This process activated an onboard ballistic parachute; however, because the aircraft was flying below the 47-meter minimum effective deployment height, the parachute failed to fully inflate. The drone subsequently struck the ground in a concrete area near the building, resulting in substantial damage to the airframe, propellers, and mounting hardware. No injuries were reported.
The investigation
The AAIU examined the flight logs, the aircraft's technical specifications, and the operational procedures used by the operator. The investigation looked into the mission planning process, which involved a Mission Controller, a Remote Pilot, and a Visual Observer. Investigators also reviewed the 2D mapping software used to identify delivery locations and the meteorological conditions at the time of the accident.
Findings
- The aircraft was operating without an automatic obstacle collision avoidance system.
- The 2D mapping tool used by the crew made the roof of the adjacent apartment building appear to be a flat, ground-level grassy area.
- Due to this visual misidentification, the aircraft descended to a level below the building's roofline.
- Turbulent air near the building caused the aircraft to drift laterally into the structure.
- The deployment of the ballistic parachute was ineffective due to the low altitude of the aircraft at the time of activation.
- Discrepancies between different regulatory definitions of an "accident" may cause confusion for operators regarding mandatory reporting requirements.