What happened
On February 24, 2011, a PZL W-3AS helicopter, registration SP-SYA, operated by LPU «Heliseco» Sp. z o.o., was performing external cargo operations in the La Caldera de Taburiente National Park on the island of La Palma. The mission involved transporting various loads, including a water purifier tank, using a 20-meter steel cable attached to the aircraft's barycentric loading hook.
After delivering a tank to a designated drop-off point, the crew was instructed by ground personnel to return to the staging area without a load, as the next cargo item was too far inside a gorge to be retrieved immediately. During the return flight, the helicopter was traveling at an indicated airspeed of 225 km/ . After climbing slightly, the aircraft experienced a sudden destabilization. The lower end of the unloaded 20-meter sling had caught on the terrain, causing the helicopter to enter a severe counterclockwise rotation.
The pilot instructed the flight engineer to shut down the engines to initiate an autorotation and perform an emergency landing. While the rotation was eventually halted, the aircraft was trapped in a narrow valley with insufficient speed to maintain flight. During the subsequent flare maneuver, the forward speed was not fully neutralized, leading to a violent ground impact and the aircraft overturning on its left side. The crash resulted in two serious injuries to the crew.
The investigation
The CIAIAC examined the flight data recorder (FDR), the cockpit voice recorder (CVR), and the wreckage. The investigation focused on the flight dynamics during the destabilization, the crew's adherence to emergency procedures, and the discrepancies between the operator's manuals and the aircraft's flight manual.
Investigators found that the crew was flying at a speed significantly higher than the limits established in the operator's manual and in violation of the aircraft's flight manual, which prohibits flying with a loose sling cable except during hover maneuvers. Furthermore, the investigation revealed that while the pilot ordered the engines to be shut down, the flight engineer only placed them at idle, failing to follow the required emergency procedure.
Findings
- The primary cause of the accident was flying at an altitude that failed to ensure adequate separation from the terrain while the external sling was unloaded, allowing the cable to snag on the ground.
- The work planning for the mission was deficient, as the crew was not prepared for the requirement to fly back to the staging area without a load.
- There were significant contradictions between the operator's Operations Manual and the aircraft's Flight Manual regarding the permitted speed and procedures for flying with an unloaded sling.
- The flight engineer did not strictly adhere to emergency procedures by failing to shut down the engines as instructed and required by the manual.