It may not be easy for airport developers � pri vate or state-owned � to incre ase user development fees collected from air travellers on the pretext of not being able to make enough money to repay their loans or get dec ent returns on investments.

Instead, airport develop ers may be asked to partly cross subsidise air serv­ices ope rations from earn ings thr o ugh real estate in and around airport, hos p itality, retail and other services.

The civil aviation min istry is understood to have favoured a hybrid till, as a revenue model that allows for apportioning revenue from aeronautical operati ons and non-aeronautical services. This is against single till model that was proposed by the Airports Economic Regulatory Auth o r ity (Aera) of India.

Sustainable revenue mo d els are being worked out by Aera to enable companies like GMR group that deve loped Delhi airport and GVK group that are expanding the Mumbai int er national air port to make their operati ons commer cially viable. Even state-owned airports developer, Airports Authority of India (AAI) has been pushing for a sustainable revenue model to run metro and non-metro airports.

Three revenue models, single, hybrid and dual till are being considered by the Aera and civil aviation min istry. In single till, the entire revenue generated from non-air business in airports is clubbed with that of air ser vices. In the case of hyb rid till, only a certain perc en tage is clubbed, where as in dual till model there is no clubbing of revenues.

Private airport develop ers, at least, in private admit that revenues from comm ercial and air services should not be clubbed. They have been pushing for flexibility to enhance development fees payable by air travellers.