CDL-AD(2006)009 - 22 - of the other State party on landing or departure, and to inspect the certificates and other documents prescribed by the Chicago Convention (Article 16). 93. State aircraft do not enjoy the overflight rights of civil aircraft. According to Article 3 (c), state aircraft are not permitted to fly over or land in foreign sovereign territory otherwise than with express authorisation of the State concerned, and in harmony with the terms of such authorisation. Such authorisation must be given by special agreement “or otherwise”; the practice of States indicates that the preferred form is a bilateral or multilateral agreement between the States concerned, valid for a given period of time, one year for example, or general permissions, or “ad hoc” permissions properly obtained through the diplomatic channels. In the latter case, the diplomatic notes are to be submitted to the competent authorities - to the Ministry of Foreign Affairs, for example - prior to the operation of the flight and usually contain inter alia the name of the foreign air operator, the type of aircraft and its registration and identification, the proposed flight routing (including last point of departure outside the State, the first point of entry, the date and time of arrival, the place of embarkation or disembarkation abroad of passengers or freight), the purpose of the flight (number of passengers and their names). 94. If “state aircraft” enter the foreign sovereign air space without a proper authorisation, they may be : - intercepted for purposes of identification; - directed to leave the violated air space; - directed to land for the purpose of further investigation/prosecution; - forced to land for further investigation/prosecution58. 95. Under customary international law59, state aircraft enjoy immunity from foreign jurisdiction in respect of search and inspection. Accordingly, they cannot be boarded, searched or inspected by foreign authorities, including host State’s authorities, without the captain’s consent. However, because state aircraft need authorisation to enter another State’s airspace, the extent of their immunity is conditioned on such an authorisation pursuant to Article 3 (c) of the Chicago Convention60. 96. A mere operational air traffic control clearance for the flight is not sufficient to satisfy the requirement for permission under Article 3 (c)61, unless this corresponds to an accepted practice. 97. Article 3bis para. b) of the Chicago Convention provides that: [E]very State, in the exercise of its sovereignty, is entitled to require the landing at some designated airport of a civil aircraft flying above its territory without authority or if there are reasonable grounds to conclude that it is being used for any purpose inconsistent with 58 See M. Milde, “Status of military aircraft in international law”, address at the Third International Law Seminar of 28 August 1999, op. cit. 59 The United Nations Convention on Jurisdictional Immunities of States and their Property, signed on 1 March 2004, provides in its Article 3 § 3 that “The present Convention is without prejudice to the immunities enjoyed by a State under international law with respect to aircraft or space objects owned or operated by the State”. 60 See Pellet, Dailler, Droit International Public, op. cit., p. 1252 ; A. Cassese, Terrorism, Politics and Law, op. cit., p. 39. 61 See “Status of military aircraft in international law”, address at the Third International Law Seminar of 28 August 1999, by Professor Michael Milde, formerly the head of the legal bureau of the International Civil Aviation Organisation, at: http:// www.mindef.gov.sg/dmg/ls/Il399.doc.