What happened
On June 20, 2014, at 06:48 UTC, a Robinson R22 BETA II helicopter, registration OK-LPS, was performing a scheduled flight from Roudnice nad Labem (LKRO) to Skuteč (LKSK). Approximately 16 minutes into the flight, while near the northwest edge of the village of Hlavenec, the crew heard a loud impact from the engine compartment. Simultaneously, the low rotor RPM warning signaled, and both the engine and main rotor RPM dropped to 90%.
The pilot immediately responded by lowering the collective to enter autorotation and applying cyclic input to attempt to maintain rotor speed. While the pilot managed to avoid nearby buildings and trees, the rotor RPM increased only slowly. During the final phase of the descent, the pilot attempted to arrest the vertical sink rate by pulling the collective, but the aircraft struck the ground heavily at approximately 3 meters AGL on a field. The impact caused significant damage to the airframe, including a cracked windshield, deformed fuselage, and a broken tail boom.
The investigation
The ÚZPLN investigation focused on the mechanical condition of the drive system and the flight sequence. Investigators examined the wreckage and recovered fragments of the drive belts. The inspection confirmed that the engine and its primary systems were functioning normally prior to the failure. The investigation also reviewed the maintenance history of the belts, which had been in service for 1,409 hours, well within their 2,200-hour service life limit.
Findings
- The pilot was fully qualified, experienced in the aircraft type, and performed the emergency procedures in accordance with the flight manual.
- The aircraft was within its maximum takeoff weight and all systems were functional prior to the incident.
- The investigation determined that the progressive destruction of both sets of dual V-belts in the main rotor drive system was the primary cause.
- The failure began with the destruction of the rear dual V-belt due to operational wear, which then caused the front dual V-belt to fail and slip off the pulleys.
- The remaining belt fragments were unable to transmit sufficient power to maintain rotor RPM, complicating the autorotation process.
- The heavy landing and resulting injuries to the two occupants (both serious) were a direct consequence of the loss of power and the difficulty in maintaining rotor RPM during the final descent.