An aircraft propulsion system including a turbojet and heat exchanger system including a heat exchanger. A supply connection and evacuation connection are forward, and aft are a transfer connection and a scoop connection, a supply pipe connected to the supply connection, and which bleeds hot air from the compression stages. A transfer pipe connected to the transfer connection transfers hot air to an air management system. A scoop connected to a scoop connection bleeds cold air from a fan duct and an evacuation pipe, including an inlet connected to the evacuation connection and an outlet, which emerges on the outside, where hot air through the heat exchanger from the supply pipe to the transfer pipe passes along a first transfer direction and cold air passes through the heat exchanger from each scoop to the inlet along a second transfer direction parallel to the first transfer direction in the opposite direction.