What happened
In the early hours of 10 August 2010, a Chinook HC2A, registration ZA708, was conducting a high-priority resupply mission as part of Joint Helicopter Force (Afghanistan). The mission involved transporting passengers and under-slung loads (USL) between Camp Bastion and various patrol bases in the Task Force Helmand area.
During the second phase of the operation, the aircraft approached PB Bahadur to deliver a 3.5 tonne load. To maintain necessary separation from obstacles, the crew utilized a 3-metre extension strop. As the aircraft entered the landing site, it encountered significant recirculating dust. Shortly after the load was released, the port side of the helicopter struck the patrol base compound wall. This impact caused the collapse of an adjacent building's roof, leading to one fatality when a serviceman was fatally injured by the falling structure.
Following the collision, the aft rotor blades struck a sangar structure within the compound. Despite the damage, the crew managed to regain a level attitude and climb away from the dust cloud. The crew performed a successful emergency running landing in a field approximately 260m from the original landing site.
The investigation
The investigation examined the aircraft's flight path, the environmental conditions, and the technical aspects of the load release. Investigators reviewed the mission planning, noting that a last-minute change in the landing location necessitated adjustments to the flight plan. The investigation also looked into the use of the 3-metre extension strop and how the dust cloud affected the pilot's visual references.
Technical assessments were conducted on the aircraft's systems, including the Winch Operator's Grip (WOG) and the radar altimeter settings. The recovery of the aircraft involved significant engineering efforts to prepare ZA708 for an aerial lift, which included stripping sensitive avionics and using demolition charges to deny engines and rotor blades to insurgent forces during the extraction process.
Findings
- The primary cause of the collision was the loss of visual references due to significant dust recirculation during the load release.
- The use of a 3-metre extension strop increased the aircraft's height, which potentially made maintaining hover references more difficult in the dusty environment.
- A last-minute change to the mission profile compressed the crew's pre-sortie preparation time.
- The impact with the compound wall caused the structural failure of an attached building roof, directly resulting in the death of a serviceman.