Air India Express, the low-cost subsidiary of Air India (AI), would pay an annual royalty to the parent company after it starts operations to the Gulf next month-end.The royalty would be paid for the use of AI's bilateral rights for the Gulf sector, official sources said today."Some money will be contributed by AI Express to AI as royalty for operating on the Gulf routes in order to enhance the revenue of the parent company," they said.The no-frills carrier would also be asked at a later stage to take over some domestic operations of AI from Indian Airlines besides carrying out its global operations.Beginning April-end, AI Express will fly a total of 37 flights a week primarily to Abu Dhabi and Sharjah. While three of these flights will operate from Mumbai and Delhi, 31 services will operate from Kerala.