Regional airline Flybe has cancelled dozens of flights on Wednesday morning for what it describes as "operational reasons".
Five flights from Belfast City Airport and four from Birmingham are among those affected, along with departures from Southampton, Aberdeen, Edinburgh and Newcastle.
Most of the flights are within the UK.
The airline said it would like to "sincerely apologise for any inconvenience caused".
"All customers affected have been emailed and advised they can rebook for travel on an alternative flight or apply for a full refund," the company said in a statement.
Customers vented their frustration on social media.
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On Monday, Flybe passengers on a new route were left with a six-hour coach journey when their aircraft was grounded.
The 18:40 service from Newquay to Heathrow could not take off on Sunday because of a "technical issue".
Cornwall Airport Newquay said passengers were offered "rebooking for another flight or ground transport to London Heathrow".
Flybe was bought early this year in a rescue deal following poor financial results.
Connect Airways, a consortium led by Richard Branson's Virgin Atlantic, paid a total of £2.8m for Flybe's assets and operations.
The Exeter-based regional airline put itself up for sale last November, following a profit warning the previous month.
Virgin, Stobart Air and Cyrus Capital set up Connect Airways in December.
Flybe fell into difficulty in 2017, after what was considered a too-aggressive expansion strategy. The company ran up a near-£20m loss in the financial year ending 31 March 2017.
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Passengers were booked onto a brand new route from Newquay to Heathrow but ended up on a coach
This January, one employee was moved to send an email accusing the firm's directors of ruining a profitable company.
The employee, a senior pilot, addressed the email to Flybe's chief executive, Christine Ourmieres-Widener.
"Congratulations, in two years at Flybe you and your fellow incompetent cohorts have managed to totally destroy a viable airline which was making profits when you took over," he wrote.
The BBC understands that the airline has suspended the pilot.
Flybe told the BBC that "an individual was suspended on 17 January 2019 in accordance with company policy".
Broken Q400s? or Something deeper?