Whether under a particular lease agreement the lessor of the aircraft is engaged in foreign air transportation is a question of fact to be determined in the light of all the facts and circumstances. However, in circumstances where the lessor furnishes both the aircraft and the crew, there is a presumption that true operational control and safety responsibility are exercised by the lessor, and that the agreement constitutes a charter arrangement under which the lessor is engaged in foreign air transportation. The burden shall rest upon the applicants for disclaimer of jurisdiction in each instance to demonstrate by an appropriate factual showing that the operation contemplated will not constitute foreign air transportation by the lessor.