Budget airline Ryanair was battling to deal with the 2,100 flights it cancelled this week after an error caused by a mix-up of pilots' holidays, which could be followed by further problems with repercussions for its growth plans.
Ryanair is cancelling between 40 and 50 flights every day for the next six weeks as it seeks to deal with a backlog of holidays from its pilots, with the cost to the company estimated to total as much as 20m euros.
The Irish airline could also be facing a second wave of flight cancellations as pilots prepare to reject a bonus offer if they give up days off, with the Guardian reporting that Ryanair pilots had drafted a letter rejecting the offer and warning they will now "work to rule".
Earlier on Wednesday, the Dublin-based carrier said that all 315,000 affected customers had been informed of the cancellations, with 55% of those being rebooked onto other flights, 63,000 flight refunds processed, and hopes for 95% of the cancellations to be resolved by the end of the week.
A day before boss Michael O'Leary faces shareholders at the group's annual shareholder meeting, communications manager Kenny Jacobs was heaping on the apologies.
"We apologise sincerely to each and every one of the 315,000 customers whose original flights were cancelled over a 6 week period in September and October, while we work to resolve this short term rostering failure," Jacobs said.
"We have taken on extra customer service teams to speed up the rate at which we accommodate and action alternative flight requests or refund applications. We expect to have the vast majority of these completed by the end of this week."
Repercussions of the cancellations were predicted for the company's M&A hopes in Europe.
In a note to investors on Tuesday, HSBC said industrial relations were likely to be "distracting management and investors".
Further analysts added: "Ryanair's assertive stances towards labour as well as governments and regulators will not help it in its efforts to take advantage of the politically sensitive restructurings at Alitalia and Air Berlin."
In reference to the sale of Alitalia, Italian transport minister Graziano Delrio said the impact of the cancellations was "very serious" and that his department "will monitor the situation, but we can't make allowances for such a huge amount of disruption".