What happened
On 5 September 2000, a Bolkow BO-105DB, registration G-AZOR, was operating as a Helicopter Emergency Medical Service (HEMS) flight near Brentwood, Essex. The crew was en route to provide medical assistance to an injured child. As the aircraft approached the landing site, the pilot observed a marshaller positioned in a large, stubble-covered field bounded by trees.
While performing an orbital reconnaissance at 300 feet to check for obstacles, the pilot identified no immediate obstructions and initiated a 'Class 1' approach toward the southwest. During the descent, as the airspeed was being reduced, the crew suddenly identified power lines directly in their flight path. Despite attempts to avoid the obstacle, three wires struck the aircraft just beneath the cockpit bubble. The impact caused one wire to break, and as the pilot maneuvered to disentangle the aircraft, a second wire snapped. The collision resulted in the detachment of the aircraft's ADF aerial and caused a fire to start in the stubble field due to the broken line.
There were no injuries to the three crew members, and the pilot successfully completed a normal landing near the intended target.
The investigation
The AAIB investigation examined the circumstances of the approach and the visibility of the hazard. The investigation established that the pilot had conducted a reconnaissance orbit to scout the landing area. The pilot noted that the power lines were difficult to see and that sunlight was not a contributing factor to the lack of visibility. The investigation also considered the potential utility of onboard wire cutters, noting that while such equipment might have prevented the entanglement, they are not a standard requirement due to the weight and performance penalties they impose on the aircraft.
Findings
- The primary cause of the incident was the unobserved encounter with power lines during the final approach phase.
- The power lines were positioned in a manner that made them difficult to detect during the initial reconnaissance.
- The impact with the wires led to the detachment of the ADF aerial and the ignition of the field surface.