Ryanair's Chief Operations Officer has decided to resign, the airline announced this evening.
Michael Hickey has spent nearly 30 years with Ryanair, having joined the company in 1988 as an engineer.
He has been in the role of Chief Operations Officer since 2014 and will finish up at the end of this month.
"Over the past 30 years Mick Hickey has made an enormous contribution to Ryanair, especially the quality and safety of our engineering and operations functions," said Ryanair boss Michael O'Leary.
"He will be a hard act to replace, which is why we are grateful he has agreed to continue in an advisory role to smooth the transition to a successor," added Mr O'Leary.
In mid-September Ryanair announced it would be cancelling up to 50 flights a day from its schedule for the next six weeks, up to the end of October, due to a backlog of holidays for pilots and crew members.
The airline was criticised by customers and the Commission for Aviation Regulation.
The Commission for Aviation Regulation said Ryanair will have to pay compensation to passengers whose flights have been cancelled with less than two weeks' notice.