What happened
On July 7, 2020, a Bell 206-L4 helicopter, registration TG-HEC, was conducting flight training maneuvers in the department of Santa Rosa, Guatemala. The flight originated from La Aurora International Airport, with a planned stop in Santa Lucia Cotzumalguapa, Escuintla, before proceeding to the El Caobanal farm for instructional exercises.
During the execution of an autorotation landing maneuver at the El Caobanal farm airstrip, the aircraft experienced a critical flight dynamic event. As the crew performed the emergency landing practice, the main rotor blades experienced flapping that caused them to strike the tail boom. The impact resulted in structural damage to the tail boom, the tail rotor drive shaft, and the stabilizer. The crew members were able to exit the aircraft uninjured.
The investigation
The DGAC/UIA investigation focused on the mechanical state of the aircraft and the flight dynamics during the maneuver. Investigators examined the wreckage, noting significant damage to the tail boom and the breakage of the drive shaft axis due to the rotor blade impact.
Maintenance records for TG-HEHD were reviewed, confirming that the aircraft was maintained according to the manufacturer's program and was in an airworthy condition at the time of the flight. The investigation also assessed the crew's qualifications, finding that both the instructor and the student pilot held the appropriate ratings for the operation. Meteorological conditions at the time of the accident were found to be favorable and did not contribute to the event.
Findings
- The primary cause of the accident was an excessive aft cyclic control input during the autorotation maneuver.
- This control input induced rotor blade flapping, leading to the main rotor blades striking the tail boom.
- The impact caused severe structural damage to the tail boom, the stabilizer, and the tail rotor drive shaft.
- The crew was performing a planned instructional flight involving emergency landing practices.