Ryanair’s chief executive apologized to shareholders and customers on Thursday, looking to stanch criticism over the cancellation of more than 2,100 flights after it scheduled too many pilots for vacation.

The budget airline — known for ultralow prices that it combines with charges for services most airlines offer for free, like airport check-in and reissuing a boarding pass — has faced a wave of customer anger over the move to cancel the flights over a six-week period this month and next month.

The move, which affects about 315,000 customers flying through airports across Europe, has cost it 25 million euros, or about $30 million, and sent its shares 3 percent lower since it first announced the cancellations on Friday.

It has prompted a strong reaction, even by Ryanair’s standards — the airline often notes that while its customers may complain about how they are treated compared to full-service carriers, they often continue flying with Ryanair because of its bargain fares.