What happened
On June 18, 2011, at approximately 15:14 UTC, a PZL W-3AS helicopter, registration SP-SUI, was performing a training flight for a fire brigade near Tabuyo del Monte, León. Shortly after takeoff, while at an altitude of approximately 45 meters, a significant torque imbalance developed between the two engines. The torque on engine #1 began to decrease rapidly, with the difference between the two engines reaching 80% within seconds.
As the aircraft climbed over sloping terrain, the crew attempted to manage the emergency. The pilot in position #1 transferred control to the commander. During the descent, the crew attempted to navigate around power lines, but the aircraft eventually struck the treetops. The impact caused the main rotor blades to break and the tail cone to separate from the fuselage. Despite the destruction of the aircraft, all 11 occupants (two crew members and nine passengers) survived with only minor injuries.
The investigation
The investigation focused on the cause of the torque divergence and the crew's response to the engine malfunction. Technical inspections of the wreckage revealed that the power control lever for engine #1 had been placed in the MANUAL position during the flight. While the fuel quality was confirmed to be within specifications, investigators noted that the compressor blades of engine #1 showed significant damage, and some impurities were found in the fuel pump filter.
Investigators also examined the crew's performance. The cockpit voice recorder captured the crew's dialogue, which revealed a lack of precise communication and a failure to follow the established emergency procedures outlined in the flight manual. The investigation also noted that the crew's focus on managing the engine imbalance and terrain clearance likely prevented them from notifying the passengers of the emergency.
Findings
- The primary cause of the accident was the incorrect execution of the emergency procedure by the crew following the torque imbalance.
- A significant torque difference developed between the engines, characterized by a rapid drop in engine #1 torque and compressor revolutions.
- The power control lever for engine #1 was moved to the manual position, but the crew failed to properly stabilize the engine parameters.
- The crew demonstrated poor Crew Resource Management (CRM), including imprecise terminology and a lack of effective communication between the two pilots.
- The aircraft was operating under a wet lease arrangement between LPU Heliseco sp. z o.o. and Hispánica de Aviación, S.A., with pilots from different organizations flying together.