Fairing device for nacelle of an aircraft propulsion power unit

A nacelle, a part of which is the fairing device, surrounds a gas turbine engine and a support pylon on an aircraft fuselage. The pylon extends into a substantially horizontal plane of symmetry containing the longitudinal axis of the propulsion power unit, and includes a central compartment that is open on the top and on the bottom and provided for housing devices. The pylon is attached to the fuselage by a distal edge extending parallel to the longitudinal axis of the propulsion power unit. The fairing device includes an upper half-cowl (2) and a lower half-cowl substantially symmetrical relative to the plane of symmetry, and lockable therebetween, in a closed position. The upper half-cowl and lower half-cowl are individually pivotably mounted on the distal edge of the pylon such that, in an open position, access is provided at the same time to the engine and to the central compartment of the pylon.