What happened
On March 10, 2018, a Cabri G2 helicopter, registration OK-CAB, was performing training maneuvers at Hradec Králové Airport (LKHK). The flight was part of a type conversion training program, with a student pilot and a flight instructor performing a series of autorotations. Following an initial unsuccessful attempt at a landing without engine power recovery, the crew proceeded with a second attempt targeting taxiway Charlie.
During the final phase of the landing maneuver, the pilot executed a flare at approximately 50 ft AGL, resulting in a significant nose-up attitude of over 30 degrees. As the pilot attempted to level the aircraft at 20 ft A/GL, they prematurely raised the collective lever. This action caused a loss of rotor RPM. The helicopter touched down on the edge of the runway with the rear skid first. The impact caused the aircraft to pitch, leading the pilot to react with an energetic cyclic input. This maneuver caused the main rotor disk to tilt, resulting in the main rotor blades striking the tail boom.
The investigation
The ÚZPLN investigation examined the aircraft, the flight crew's statements, and security camera footage from the airport. The investigation established that the aircraft was in a fully airworthy condition with no mechanical failures or control malfunctions. The crew's medical certificates and licenses were valid, and the pilot was performing the maneuvers under the instructor's supervision. Technical inspections of the wreckage confirmed that the damage to the tail boom, Fenestron, and main rotor blades was solely caused by the impact of the main rotor blades.
Findings
- The pilot, while performing an autorotation without engine power recovery, executed an excessive flare that significantly increased the aircraft's pitch.
- The pilot raised the collective lever prematurely before the aircraft had leveled out, leading to a critical loss of rotor RPM.
- The pilot's instinctive and energetic cyclic input following the touchdown caused the rotor disk to tilt into the tail boom.
- The instructor, although prepared to intervene, did not react quickly enough to prevent the improper control inputs during the critical phase of the flare.
- The pilot's previous flight experience on Robinson R22 and R44 helicopters, which utilize different landing techniques, likely contributed to the improper handling of the Cabri G2 during the maneuver.