The present disclosure relates to a propulsion assembly having a nacelle surrounding a turbojet engine, the nacelle having an upstream structure with an air inlet including an air inlet lip, the air inlet lip defining, with the air inlet lip, an air inlet chamber, the upstream structure being capable of translational movement along an axis parallel to a longitudinal axis of the nacelle, between a closed position and an open position that allows access to the turbojet engine. The propulsion assembly further includes at least one locking/unlocking device allowing and preventing movement of the upstream structure that in one form is fixed to the air inlet lip and to an upstream flange of the turbojet engine.