Under Section 39 of the Airports Authority of India Act, 1994, where the Central Government supersedes the Authority on grounds of grave emergency or persistent default, for what maximum period can such supersession be notified?

Section 39(1) empowers the Central Government, by notification in the Official Gazette, to supersede the Authority where satisfied either that it is unable to discharge its functions on account of a grave emergency, or that it has persistently defaulted in complying with Central Government directions or in discharging its statutory duties, thereby endangering India's security or aviation interests. Such supersession can be notified for a period not exceeding six months. During supersession, all powers and duties of the Authority are exercised by such person(s) as the Central Government appoints, and existing members vacate office, though the Authority must first be given a reasonable opportunity to make representations against the proposed supersession.