What happened
On May 10, 2019, an AK1-3 ultralight helicopter was undergoing testing and flight trials following assembly by a mechanic from the manufacturer's Ukrainian company. The aircraft, registered as SP-HLLK, had undergone a successful initial flight earlier that day.
At approximately 12:30 local time, the crew commenced a second flight, intended as a sightseeing mission, in the vicinity of Sokołów Podlaski. Roughly ten minutes into the flight, the pilot observed a progressive decline in both the engine and main rotor RPM. Despite attempts to increase power using the collective and throttle controls, the RPM levels dropped below the minimum allowable limits.
Facing a critical loss of power, the pilot initiated an emergency landing in an unprepared field, transitioning the aircraft into autorotation. The helicopter struck the ground in a horizontal attitude with a high rate of descent. The impact caused the tail boom to separate from the fuselage, and the aircraft subsequently overturned onto its right side. The engine shut down automatically upon impact, and no fire occurred as the fuel tank remained intact.
The investigation
The PKBWL investigation focused on the mechanical failure and the regulatory status of the aircraft's markings. The investigation established that the engine used was an EJ25 model, which was not certified.
Furthermore, the investigation identified a discrepancy in the aircraft's identification. While the airframe's documentation and the landing gear frame identified the aircraft as SP-HLLK, the tail boom bore the registration SP-HLIK. The pilot stated this was due to a printing error by the supplier of the registration decals. The commission noted that the aircraft was being operated in violation of aviation regulations regarding required identification markings.
Findings
- The primary cause of the emergency landing was a progressive loss of engine and main rotor RPM that could not be recovered through pilot intervention.
- The landing resulted in two light injuries to the crew.
- The impact caused significant structural damage, including the destruction of the tail boom, damage to three main rotor blades, and damage to two tail rotor blades.
- The skid landing gear functioned as intended, absorbing a significant portion of the impact energy, which mitigated the severity of the crash for the occupants.