Section 4(5)(iii) in The Airports Authority of India (Major Airports) Development Fees Rules, 2011
(iii)any balance amount remaining after the entire amount of development fees as approved by the Airports Economic Regulatory Authority is paid, shall be transferred to Development Fees Surplus Account and the said amount shall be used for authorized investment by the Authority and the balance available, if any, in this account may be appropriated for subsequent determination of development fees.