When a craft is registered, and its pilot has his certificate, it is considered necessary that--before he has a right to fly--he should apply for an official form, which would be known as a permit to travel. This would contain all necessary details for the identification of himself and his machine, and would allow him to fly anywhere within his own country: but it would not be available for an aerial tour abroad. He would be required, before starting upon a foreign flight, to give up this home permit, and obtain in place of it a special Customs’ bulletin. This would specify the nationality of the machine, give particulars of its registration, and provide details as to its passengers, goods, and baggage; also the date and place of its departure from England, with the destination to which it was bound. On landing abroad, the airman would hand to the authorities his bulletin, and receive in exchange a document showing that the Customs’ officers had examined his machine and that he had paid what duty might be claimed on any goods he carried; then, once he had this new document, he would be free to fly in the country visited. It is in regard to the Customs that the greatest problem must be faced. Rules may be made, alighting points insisted upon, but how are aerial smugglers to be caught? It has been suggested that there should be a Customs’ police, provided with fast-flying machines; also that if a machine failed to descend when it ought, they should go in chase of it. But in days when, without once alighting, a flight of twenty-four hours will be easily accomplished, such officers might find themselves upon a wearisome pursuit; besides the probability that, either during the night or in a fog, they would be given the slip. Rendering easier aerial smuggling is the fact that, to discharge a small cargo of contraband over a given spot, the pilot need not alight. Fixing the package to a parachute, he could cast it free from his machine and continue swiftly upon his way--the parachute being secured with its burden by the confederates who were below. So difficult, in regard to aircraft, is this question of applying the Customs, that it has been argued air-borne traffic should--to save endless trouble and great expense--be allowed to go duty free.