Councillors at Derry and Strabane District Council have heard that almost £6m is required to ensure City of Derry Airport can continue to operate beyond 31 March 2021.
The figure emerged at the authority's governance and strategic planning committee on Tuesday.
Councillors gave their approval to request additional money from central government.
This would be to secure the airport's sustainability beyond 31 March 2021.
Members were told that UK government funding subvention for the public service obligation (PSO) route from Derry to London "is currently provided at 100% until March 2021, but will reduce to 50% thereafter".
They were informed that the council "would not have the financial resources to bear this additional cost beyond that point and the full support of government or governments for the continued operation of the airport beyond March 2021 is required".
Members of the committee agreed that council "underwrite an additional sum up to £750,000 to keep the City of Derry operational to March 2021 as an interim measure to allow the airport to operate whilst engagement continues with government".
Members were informed that this additional sum "would be allocated from in-year capital savings and therefore have no recurring impact on rates".
They were also advised that beyond 2021, it is "hoped that the proposed formal engagement with central government in relation to contributions towards ongoing revenue costs would allow council's current funding to substantially reduce with associated savings then being available for other key strategic projects identified in the council's strategic inclusive growth plan".
The proposals agreed by the committee are subject to ratification by full council later in November.
Scottish airline Loganair took over the London Stansted route in February, following the collapse of Flybmi, which had operated flights between the airports since 2017.
The route now operates from City of Derry airport to Southend.
The public service obligation air route, the first of its kind in Northern Ireland, has been in place since 2017.