23.5. Customs records and national ship and aircraft registers. When aircraft and ships cross the borders of countries as items of trade and the appropriate customs records are created, those records should be used as the main source of information. However, in some countries, international trade in aircraft and ships may not be recorded by customs even if those items cross borders; also, customs records may be incomplete or non-existent if those items do not cross customs borders. Under such circumstances, many countries turn to national aircraft and ship registers for evidence of a trade transaction, using change of ownership as indicated in the register as the basis for the compilation of trade statistics. However, not all countries have national aircraft and ship registers and some might not use existing registers for statistical purposes. Further, the registers might not cover all transactions between residents and non-residents, or might not be sufficiently updated, or the information might not be suitable or sufficient for use. In particular, such registers might contain information on the legal owner while it is information on the economic ownership that is required. Therefore, in addition to registers, countries might have to consider using additional sources such as accounts of companies or reviewing leasing contracts or management contracts (for vessels) to establish economic ownership.
23.6. International requirements for the registration of aircraft. Various national and international statutory instruments govern civil aviation and the registration of aircraft. Of particular international importance is the Convention on International Civil Aviation, which specifies the principles to be recognized by signatories. The Convention states that aircraft shall hold the nationality of the country in which they are registered. It also states that aircraft may not be legally registered in more than one country, and that every aircraft used for international air transport must be marked with its nationality and registration number. At the national level, those global rules mean that every aircraft is entered in the national register when it is licensed for transport. In the case of imported aircraft, registration can occur only upon the applicant’s producing appropriate documentation; in particular, the applicant must produce proof of acquisition of ownership. However, at least in some countries, not only the acquirer (legal owner) but also the economic owner/operator can be the applicant. Also, proof of cancellation or non-registration is required, which ensures that an aircraft has actually been registered in one country only, thus ruling out duplication or incorrect recording.
23.7. International requirements for the registration of ships. As a measure for enhancing ship safety and security, the International Maritime organization (IMO) introduced in 1987 the IMO ship identification number scheme, which became mandatory for all ships as of 1 January 1996 and which is managed by IMO and IHS Fairplay (previously called Lloyd’s Register - Fairplay). Its was to aim assign a permanent number to each ship for identification purposes. That number would remain unchanged upon transfer of the ship to other flag(s) and would be inserted in the ship's certificates. Further, in 2004, the IMO Unique Company and Registered Owner Identification Number Scheme was introduced as a measure to enhance maritime safety, security and environmental protection, and to facilitate the prevention of maritime fraud. Its purpose is to assign a permanent number for identification purposes to each company and/or registered owner managing ships of 100 gross tonnage and above engaged on international voyages.,  The IMO Unique Company and Registered Owner Identification Number Scheme is managed, in parallel with the IMO Ship Identification Number Scheme (resolution A.600(15)) and procedures for the implementation thereof (Circular letter No.1886/Rev.3), without charge by IHS Fairplay.
23.8. Request for additional documentation. The statistical authority should use available customs information and aircraft and ship registers for obtaining the maximum amount of statistical information possible and, if necessary, should request the owners named on the register or the leaseholder named on the financial lease to submit separate foreign trade statistics declarations. The last-mentioned step may have to be implemented through the enactment of legislation specifying the obligation of each party (the registration authority, owners, leaseholders) to provide information.
 A similar situation might exist in the case of trains which regularly cross borders. Also, in this case, it might be necessary to use the change of ownership and not the crossing of the border as the criteria on determining whether a trade transaction is to be recorded. Enterprises that own and/or operate or produce and sell trains should be able to provide information about the acquisition and sale of trains.
 For example, in the European Union, fishing vessels are in general not registered in the national ship registers, as indicated by the results of an EU questionnaire.
 See the Convention on International Civil Aviation. Available from http://www.icao.int/publications/pages/
doc7300.aspx. There are currently 191 contracting States parties to the Convention.
 Convention on International civil Aviation, part I, chap. III, article 17.
 Ibid., article 18.
 Ibid., article 20.
 See International Maritime Organization, Circular letter No. 188/Rev.3 of 11 December 2006 on the implementation of resolution A.600(15): IMO ship identification number scheme.
 See International Maritime Organization, Circular letter No.2554/Rev.1, 7 February 2007 on implementation of the IMO Unique Company and Registered Owner Identification Number Scheme (resolution MSC.160(78)).
 Countries are invited to register ships engaged in domestic voyages as well.
 However, fishing vessels might not be registered in this standard way.