EasyJet will partly fill the slots at Gatwick Airport which will be vacated by Aer Lingus later this year.
The budget airline is adding three aircraft to its fleet at Gatwick but has not revealed where they will fly.
Aer Lingus meanwhile will take two of its Airbus A320s out of operation, reducing its fleet size to just three at Gatwick.
The move will become effective from the end of March.
The three aircraft will continue to serve three existing routes to Malaga, Dublin and Knock and a new route to Cork.
Aer Lingus has deferred delivery of two A320 aircraft originally due for delivery in October and November 2010 to April and May 2011, respectively.
Savage pay cuts, a round of redundancies and large capacity reductions means the Irish flag carrier will post a small operating profit this year.
A statement read:
“As a result of cost and capacity management actions implemented during 2009, the Group expects to report a small operating profit (before exceptional items) for the second half of 2009.
“This performance primarily reflects better than expected yields in the second half of 2009, which have been driven by removal of a long haul aircraft in September and tactical route cancellations in November.”
Passenger figures were also up in December, by 9% year-on-year to 766,000.
Easyjet’s regional general manager Paul Simmons said: “We are proud to have developed our business at Gatwick over the last few years.
“As a result of this additional capacity we plan to announce some great new routes from Gatwick for this summer within the next few weeks.”