Revenues from leasing, licenses and concessions derive from activities that are not subject to regulation. However, these activities must also be evaluated since they might generate issues that are against the public interest. For example, if rents paid by commercial area tenants are excessive in comparison to other rents in the leases market, it might be necessary to impose controls. Aeronautical charges are determined according to the single till approach. Under such an approach, airport costs and revenues are foreseen to take into account all services. Aeronautical charges are fixed in such a way as to permit a given profitability level that, in tum, depends upon previous costs and revenues estimations. Once the regulatory pricing formula is in place, the private operator might increase rents above those charged in commercial areas, and hence, act against public interests.

As we have already mentioned, if airports are subject to price regulation they may also be tempted to reduce service quality, and consequently their costs. Therefore, it is crucial to investigate the perception users have about the services provided at airports. Before carrying out any quality assessment, it is necessary to define a standard level of service that would be feasible and reasonable. Such standards would permit the airport regulator, under a penalty threat, to demand the attainment of a certain level of service.

In the British case, air carriers have argued that it is necessary to reach agreement regarding the standard level of services, as well as for provisions that would entitle them to compensation in case of non-fulfillment. They maintain that any deviation from standards would affect their service quality and that without compensation such a mechanism would not be effective. BAA, however, argues that airport services are provided jointly by airport operators and airlines and, therefore, the level of services do not depend entirely upon its performance, but also upon air carriers and handling staff. Carriers, in turn, argue that penalties must be applicable only to BAA, given that airlines operate in a competitive environment and have strong incentives to maintain and improve their quality. Nevertheless, in spite of this dispute, it is not quite clear whether the airport operator should be solely responsible for the attainment of standard levels of quality. In any case, a key aspect of this compensatory mechanism is identifying who is responsible for nonachievement of standards. Leaving aside these difficulties, in order to guarantee a certain level of service within the context of regulation, it is essential that an agreement regarding quality standards be reached.

The procedures for evaluating the factors determining the level of service in the terminal building are complex, leading to the use of such variables as "time of service" and "level of congestion" as proxies for the quality of services provided. Nevertheless, Table 5.3. shows a set of quality indicators that comprise an important part of most of the conflictive aspects of airport activities.

In a study carried out at Birmingham airport (see Mumayiz and Ashford, 1986), it was established that users perception of time of service depended upon the type of market. For European scheduled flights, a check-in waiting time of 7.5 minutes or less was considered satisfactory, while a time equal or greater than 14 minutes was perceived as intolerable. For charter flights, these limits would be respectively between 11 and 21 minutes. According to the same study, a general waiting time of not more than 12 minutes would indicate a satisfactory level of service.

_51_