“Michael Hickey ... has decided to resign effective from the end of October,” the low-cost carrier said in a statement issued late Friday.
“Over the next three weeks he will work on an orderly handover of his responsibilities, while Ryanair will commence the process of identifying and recruiting a successor.”
Last month, Ryanair was forced to cancel 20,000 flights up to March, mainly owing to a shortage of pilots.
Pilots and cabin crew have been forced to take outstanding holiday entitlement by the end of the year as part of new company rules. Ryanair also blamed air traffic control delays, strikes and weather disruption.
On Friday, it emerged that chief executive Michael O’Leary has written to pilots with a pledge to beat the pay offered by competitors and to improve working conditions over the next six months.
In the statement announcing Hickey’s resignation, O’Leary praised his “enormous contribution,” noting he joined Ryanair as an engineer in 1988 and has been in his current role since 2014.
“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 and to complete a number of large projects he is currently working on,” he said.