Accident to the Robinson R44 registered F-HLOU on 31/10/23 at Salazie
Loss of control during flight, collision with the terrain
After a first local flight over La Reunion, the pilot refuelled the helicopter from a fuel drum that he had just opened. The JAPY pump used for refuelling did not have a water detector, and the pilot did not drain the tank after refuelling to check for water in the fuel.
At the time of take-off for the second flight, the weather conditions were compatible with a VFR flight. However, a mountain breeze was beginning to develop over the Salazie area, with light to moderate turbulence due to the rugged terrain.
The pilot climbed to cross the Col des Bœufs pass (6,420 ft) and then in descent, crossed the Cirque de Salazie from west to east to reach the Voile de la Mariée waterfalls. The pilot then headed north at an estimated altitude of between 3,000 ft and 3,600 ft, following the terrain, below the ridge line, towards the pass (altitude 2,418 ft) that led to the Bras de Caverne gorge and the Trou de Fer. As he approached the pass, he called out “Turbulence Turbulence” over the radio. The investigation was unable to determine whether the pilot actually encountered turbulence related to local
wind conditions.
A few seconds later, i.e. after approximately 15 minutes of flight, the pilot transmitted two “PAN PAN” messages, each accompanied by the “LOW NR” warning indicating a low rotor speed.
The examination of the wreckage at the accident site and subsequent detailed examinations established that the engine was delivering little or no power prior to the collision with the vegetation, although no mechanical anomalies were found during the examinations.
The results of the analyses of the fuel used during the flight may explain that the turbulence perceived and the failure reported by the pilot were linked to the ingestion of water or contaminated fuel—due to the lack of draining after refuelling—which led to a loss of engine power or even an in-flight shutdown.
It was not possible to determine whether the pilot transmitted these “PAN PAN” messages due to the activation of the “LOW NR” warning or a malfunction of the engine.
The decrease in the main rotor speed and the sudden drop of the helicopter described by witnesses suggest that the pilot did not immediately take the necessary piloting actions to initiate an autorotation (immediately lowering the collective pitch control to stop while pulling on the cyclic stick) in order to maintain or restore the rotor speed to the normal operating range. The main rotor speed then decreased until lift was lost, causing the helicopter to plummet to the ground.