A new report by the Northern Ireland Audit Office (NIAO) points out that the cost to the Londonderry ratepayer of maintaining the airport rose from £1.5m in 2005/6 to £4.6m in 2008/9.
Local Government Auditor Alfred Knox also noted that the local facility had loans of £7,702,628 last March and paid loan charges of £600,000 during the last financial year.
In NIAO's Annual Audit Letter to the local authority Mr Knox acknowledges the benefits but also the considerable costs of running the Eglinton airport.
He wrote: "The Airport brings important economic benefits to the Northwest but at considerable cost to the Derry City Council ratepayer. The accounts record in the Service Revenue Account the net cash cost of the City of Derry Airport.
"This net cash cost is the cost that impacts directly on the District Fund balance and the amount needed to be raised from the ratepayer each year.
"This has increased significantly in recent years to £4.6m in 08/09 (from £3.2m in 07/08, £2.0m in 06/07 and £1.5m in 05/06). The Airport has loans of £7,702,628 at 31/3/2009 and paid loan charges of £0.6m during 2008/2009."
Mr Knox also reported that planned capital expenditure of up to £4.1m may also have to be financed through further loans.
The £4.1m figure relates to safety works at the airport, which are the subject of an application to both Governments for additional finance.
"If further grant is not forthcoming for the unfunded capital expenditure of £4.1m at the Airport, the expenditure will have to be funded by loans or applying Capital Reserves," he stated.
"The Council has reviewed the governance and operations of the Airport and decided to transfer the City of Derry Airport business into a separate company which will be owned by the Council. Consideration has also been given to disposing of the Airport business to the private sector," he added.