What happened
On August 5, 2023, a Ranabot CH77 ultralight helicopter, registration 974PT, was performing a cross-country flight from La Saline-Les-Bains toward the Mafate cirque in Réunion. The pilot was en route to meet an instructor for advanced training in mountainous terrain. At approximately 09:51 local time, the pilot transmitted a radio message indicating he was climbing toward the Deux-Bras locality.
Seconds after this transmission, the aircraft experienced a sudden loss of control. The main rotor blades struck the tail boom, causing several structural components—including the tail rotor, tailplane, and portions of the tail boom—to separate from the airframe. The aircraft entered a vertical descent and struck the ground in a wooded area, resulting in a post-impact fire. The pilot was fatally injured.
The investigation
The BEA examined the wreckage, which was recovered from a wooded area at an altitude of approximately 1,650 ft. Investigators noted that the main wreckage was destroyed by the impact and subsequent fire. Several components, including one main rotor blade and the two doors, were found separated from the main wreckage.
Analysis of the rotor blades revealed damage consistent with contact with the tail boom. Specifically, traces of paint on a detached blade matched a "Danger" sign on the tail boom. The investigation also reviewed video footage from a nearby paraglider pilot, which captured the aircraft tilting forward and losing structural integrity in less than three seconds. Regarding the aircraft's doors, investigators checked for potential failures following previous similar accidents in this model; however, the locking mechanisms appeared functional, and the separation of the doors was attributed to airframe distortion during the crash.
Findings
- The primary cause of the accident was the rotor blades striking the tail boom.
- The investigation suggests that a high-amplitude forward input on the cyclic pitch stick may have created a low load factor condition.
- Such a condition is known to cause excessive blade flapping on teetering rotor heads, which can lead to mast bumping or the blades making contact with the airframe.
- While the investigation could not confirm the exact reason for the control input, it noted the possibility that the pilot may have reacted to the proximity of a paraglider wing, though a mechanical malfunction could not be entirely ruled out.