Ferrovial of Spain, owner of BAA Ltd, has agreed to sell George Best Belfast City Airport to an ABN Amro fund for £132.5m.
The Spanish company paid £43m for the airport, which aims to handle 2.5m passengers this year, in 2003.
Although both are owned by Ferrovial, Belfast City is not run by BAA.
Its main competitor is Belfast International Airport, 15 miles to the north west of Belfast and owned by TBI, another Spanish controlled company.
Belfast City also competes to some extent with Dublin International Airport with many passengers from the Irish Republic finding it easier to travel north and use the Northern Ireland hub.
Aer Lingus is now a major operator at the airport.
Belfast City Airport has applied for planning permission for the cap on outbound ticket availability to be raised from the present 3m to 4m, with a corresponding increase of movements from 45,000 a year to 48,000.
But the night-time curfew will remain in place.
A runway extension has also been applied for and this could open up the airport for transatlantic Boeing 757 operations.
It is expected that the sale of the airport will be completed by the end of the month.
An announcement concerning the future of Southend Airport is also said to be imminent with a purchase by London City owners AIG Financial Products Corp and Global Infrastructure Partners (GIP) understood to be a distinct possibility.