What happened
On 23 March 2026 at 0247 hrs, a swarm of unmanned aircraft was conducting a night-time rehearsal for a light display above the River Thames. The operation took place in close formation near the London Eye Pier in Greater London. During the sequence, several units experienced degraded positional accuracy. Early in the flight, two drones descended out of control. Later in the programmed sequence, five additional units collided during a transition maneuver and fell into the river. No injuries were reported, but multiple unmanned aircraft were destroyed and not recovered.
The investigation
The AAIB reviewed data from the operator regarding the failure of the positioning system. The investigation established that the drones had reverted to a lower-accuracy positioning mode while in flight. This caused significant positional drift within the tight formation. Post-flight examination focused on the Real-Time Kinematic (RTK) base station antenna, which is used to enhance position sensing. Evidence indicated that this antenna may have been partially obscured during the operation, compromising the signal integrity required for precise navigation.
Findings
The primary causal factor was the loss of high-accuracy positioning due to a potentially obstructed RTK base station antenna. This led to positional drift within the swarm, resulting in uncontrolled descents and collisions between units during programmed transitions.
Safety action
The operator increased the height of the RTK antenna to improve line-of-sight. Additional pre-flight checks were introduced to verify an unobstructed signal and confirm a stable RTK fix before commencing any flight operations.