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of other nationalities is, however, necessary to comply with the Convention. Moreover, the continued adjustment of such charges to equate to the normal weight scale and therefore to keep it in relationship to cost per ton mile is believed to be necessary for a proper understanding and therefore development of the economics of air transport and of airports. 326. Coupled with the system of levying charges on aircraft, there should be vigorous development of ancillary sources of revenue. These sources are well known and understood. They comprise revenue from restaurants and other services provided for the public, car park charges, public enclosure charges, &c. The development of this source of revenue we have recommended above should be within the field of the local aerodrome committees. Other sources of revenue have been exploited in some countries. In the United States, for example, the aerodrome authority commonly makes a levy on petrol sold or sells the concession for supply of petrol and oil. This has the same effect as landing charges in that it raises the cost of air transport, but it does not result in such equitable distribution as the landing charge system. Aerodrome licensing 327. There is no need for the application of the aerodrome licensing system to State aerodromes, since a "licence " in this sense is a permit to do something which would otherwise be illegal. That does not apply to State aerodromes provided by the competent departmental authoritv. In the case of State aerodromes, all that is necessary is publication of the approval of the aerodrome for use by civil aircraft, subject to conditions prescribed. This procedure is appropriate also for Air Force aerodromes which may be made available in varying degrees and for different purposes for use by civil aircraft. What follows may be read as applicable both to the licensing of non-government aerodromes —i.e., private or local authority—and to the approval of State aerodromes. 328. The system of aerodrome licensing at present in force in New Zealand is based on the severe physical limitations of the majority of the existing aerodromes. This has necessitated a system of licensing which states categorically which types of aircraft may use a particular aerodrome under specified loading and weather conditions. This we consider to be a safe and practicable method in the circumstances prevailing. However, we feel that if this system is allowed to continue indefinitely, it will ultimately break down owing to the impossibility of specifying precisely the conditions under which each type of aircraft can operate safely under varying conditions. To keep such a system up to date will become increasingly difficult as time passes and the number of aircraft types increases. To specify safe operating conditions at every aerodrome for each type of aircraft, bearing in mind such variable