Low cost airline Flybe has cancelled flights - blaming the Easter holidays and a "shortage of pilots" among several reasons for the disruptions.
Boasting of carrying 8 million passengers a year between 81 airports across the UK and Europe, the airline issued an apology on Wednesday to its customers.
Ten Flybe flights in and out of Belfast City Airport have been cancelled.
Flights affected include services to Birmingham, and round trips to and from Leeds Bradford and Aberdeen. One flight from Cardiff Airport to Verona was cancelled.
A flight from East Midlands was also cancelled.
In a statement, a spokesperson for the airline wrote: "Flybe sincerely apologises to all our customers and partners affected by the current flight cancellations. Whilst 95% of Flybe flights are operating as per normal, we do recognise the impact of today's cancellations.
"We are doing our best to mitigate the impact of the current situation that has arisen due to a combination of factors including seasonality, pilots' end of leave year, Easter holidays, base restructuring and the shortage of pilots across the industry that Flybe has highlighted over recent months.
"We have already identified several mitigation actions and will be issuing further updates throughout the day.
"All those affected have been emailed and advised they can re-book for travel on an alternative flight or apply for a full refund."
ITV News' Consumer Editor Chris Choi has been following the announcement. He tweeted:
Cardiff Airport CEO Deb Barber has confirmed doubts of the airline's future at the Welsh airport.
She said: “Flybe’s plan to restructure and reduce its jet operations across many bases is part of the company’s long-standing objective to stabilise the business. This is a further sign to UK Government that more needs to be done to support regional flying; the uncertainty of BREXIT, currency and fuel costs are all impacting on the industry. Air Passenger Duty (APD) presents an additional cost burden, especially with the ‘double hit’ on domestic services which make up the majority of the Flybe network.
“We are working closely with Flybe to ascertain its plans moving forward and the role it will continue to have in connecting Cardiff with key routes in the UK and Europe. The winter programme will be launched shortly, but in the meantime, we would reassure passengers that the summer schedule is underway and operating as normal.
“If passengers have any queries, they should contact Flybe in the first instance.”
Passengers received texts and emails on Tuesday evening telling them of problems with their flights.
The disruption followed the launch of the airline's summer schedule.
Flybe was recently bought by the Connect Airways consortium, which includes Virgin Atlantic.