What happened
On 21 September 2019, a DJI Matrice 200 V1 was performing an automated aerial survey near Raigmore Hospital, Inverness. During the flight, at an altitude of approximately 100 m, the aircraft's ballistic parachute recovery system deployed unexpectedly. The motors ceased operation, and the drone drifted under the parachute before landing on a residential roof, sustaining significant damage to its landing gear, camera, and antennas.
Two months later, on 29 November 2019, the same aircraft—having been repaired and fitted with a new parachute unit—experienced a second deployment. While being manually flown in GPS mode over open ground in Montrose, Angus, the parachute activated at a height of 92 m. The aircraft descended into a grassy area, resulting in a dislodged battery but no injuries to persons or damage to property.
The investigation
The AAIB examined flight logs from both the aircraft and the parachute system. For the first incident, the parachute manufacturer's analysis identified an intense vibration pattern immediately preceding the deployment. Laboratory tests simulating loose mounting hardware successfully replicated this vibration-induced trigger.
Regarding the second incident, the investigation faced limitations due to missing aircraft flight logs and insufficient technical data from the UAS manufacturer. While the aircraft's logs showed several spurious warnings regarding propeller issues and vibrations, the parachute system's data indicated a sudden drop in altitude. The manufacturer suggested the second event might have been a response to a total power failure, though the aircraft remained operational after the landing.
Findings
- The first parachute deployment was likely caused by excessative vibration resulting from the parachute system not being securely fastened to the airframe.
- The second deployment's cause could not be definitively established, though a total power failure was considered a possibility by the parachute manufacturer.
- The investigation was hindered by the lack of available flight data and limited technical support from the UAS manufacturer.
Safety action
- The parachute manufacturer updated its installation guide to include checks for the security of mounting leg attachment screws.
- The operator implemented new maintenance and pre-flight procedures, including the use of thread-locking compound on mounting screws and improved documentation for hardware changes.
- Safety Recommendation 2020-016: It is recommended that DJI introduce an effective system for providing timely technical support to State safety investigations.