Passengers will hear next week if new airlines can be attracted to fill the routes left vacant by the sudden shutdown of bmibaby's Belfast flights.
George Best Belfast City Airport chief executive Brian Ambrose said he is in talks with other carriers and has set the target of getting answers within seven days.
Thousands of people in Northern Ireland have had their summer travel plans thrown into chaos by the announcement that the budget airline will stop its Belfast flights on June 11.
Mr Ambrose said he had been negotiating a potential replacements in the event of a cancellation of flights in the autumn, but was shocked by the decision to pull the plug with five weeks notice.
“For the last couple of months we have been speaking to airlines,” he said.
“We have quite a number of airlines who have expressed an interest in these routes.”
But on the timing of the bmibaby announcement, he added: “June 11 was totally out of the blue. It is just now a more difficult transition.”
He said exploratory talks had opened up potential deals with carriers who could have set up in Belfast in October.
“We are trying to find airlines who will pick up these routes,” he said.
“It's a big ask now to find an airline who can mobilise in five weeks.”
Last year, a total of 420,000 passengers - 20% of the airport's business - flew with bmibaby.
The shock decision leaves three of the airport's domestic flights and eight international routes vacant as the summer season looms.
As angry customers said they faced paying for more expensive flights, Mr Ambrose said his airport would refund anyone who had pre-booked car parking for bmibaby flights.
He said it was hoped that any of the 100 bmibaby staff in danger of losing their jobs would be taken on by new carriers or ground crews who might be attracted.
But he accepted the future was uncertain: “It is a worrying time for thousands of customers. It is a worrying time for staff.”
He said the airport had recovered from similar blows in the past, but the difficulty was the tight timeframe.
Mr Ambrose said his team was working “day and night” to fill the vacant routes, adding: “The next seven days will be important.”
The trade union Unite attacked the plan to shut down bmibaby operations at Belfast City Airport, branding it a “lamentable decision”.
Unite regional industrial organiser David McMurray: “bmibaby has been offering the Ulster travelling public alternative routes to the UK and Europe and this decision by International Airlines Group (IAG), the owners of British Airways, who recently bought over BMI, has come as a total shock for the public and the staff.”
Meanwhile, Consumer Council chief executive Antoinette McKeown said she was to challenge BMI's new owners on a number of issues, including the timing of the Belfast decision.
She said: “Why are British Airways withdrawing bmibaby from Belfast in advance of the busy holiday season when other bases around the UK are to stay open until the autumn?”
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