On 25 March 2018, an ATR 42-500 main landing gear bay door weighing 15kg detached shortly after a night descent had begun but this was unknown until the flight arrived at Aurillac. The Investigation found that the root cause of the detachment was a loose securing nut which had triggered a sequence of secondary failures within a single flight which culminated in the release of the door. It was concluded that the event highlighted specific and systemic weakness in relevant airworthiness documentation and practice in relation to the lost door and the use of fasteners on this aircraft type generally.