DUBLIN — Ryanair (RYAAY.O) chief operations officer Michael Hickey will resign from the end of the month, the under-fire airline said on Friday, becoming the first executive to leave since a rostering mess-up led to the cancellation of thousands of flights.

Hickey was responsible for rosters when the disruptions began but that function was taken over by Ryanair's Chief People Officer, Edward Wilson, on Sept. 27 when the Irish airline announced its second wave of cancellations.

"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. He will be a hard act to replace," Ryanair chief executive Michael O'Leary said in a statement.