What happened
On 10 August 2016, a PZL W-3AS, registration SP-SUC, operated by Hispánica de Aviación, was engaged in firefighting operations near Villa de Mazo, Spain. The aircraft was part of a mission to suppress a fire, having already completed 12 successful water drops from a suspended bucket containing 1,100 liters of water.
While approaching a specific target site at a low speed of approximately 30 knots, the helicopter encountered a left tailwind. During this maneuver, the aircraft began to yaw to the left at an increasing rate. The pilot attempted to compensate using right pedal inputs, but the aircraft became uncontrollable. The helicopter entered a descending spiral, striking pine trees before impacting the terrain. The two crew members on board escaped without injury, though the aircraft sustained significant damage and a fire broke out in the left engine following the impact.
The investigation
The CIAIAC investigation examined flight recorder data, which revealed that the pilot's actual control inputs—specifically raising the collective and moving the cyclic backward—differed from the pilot's recollection of attempting to increase speed and reduce power. The investigation also reviewed the aircraft's mechanical systems, finding no malfunctions in the flight controls, tail rotor pitch change system, or hydraulic actuators. The investigation further analyzed the regulatory landscape regarding pilot training for the Loss of Tail Rotor Effectiveness (LTE) phenomenon.
Findings
- The primary cause of the accident was a loss of tail rotor effectiveness (LTE), which the pilot was late in identifying.
- The aircraft was operating at a low airspeed and low altitude, within a flight envelope that lacked sufficient translational lift.
- The crew did not release the water from the bucket or release the external load, actions that could have reduced power requirements and helped regain control.
- The pilot's control inputs, as recorded by the FDR, did not align with the intended recovery maneuvers.
- There was a lack of specific training and proficiency checks regarding emergency maneuvers involving external loads and the LTE phenomenon.
Safety action
- REC 27/17: Recommended that EASA standardize theoretical and practical LTE training across various helicopter license programs.
- REC 28/17 & REC 29/17: Recommended that Spanish authorities (DGAC and AESA) regulate LTE training for pilots involved in firefighting and search and rescue.
- REC 30/17: Recommended that AESA require operators to include LTE refresher knowledge in their Operations Manuals.
- REC 31/17: Recommended that the operator include emergency maneuvers with external loads in their proficiency checklists.