It's led to the cancellation of thousands of flights.
The Irish airline, the largest in Europe by passenger numbers, has in recent weeks disrupted the plans of more than 700,000 passengers by failing to have enough standby pilots to ensure the smooth operation of its schedule.
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 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.
O'Leary told Ryanair's annual shareholder meeting last month that while the shortages were created by mismanagement in its rostering section, he took personal responsibility for the "cock up".
Asked by an investor at the Sept. 21 meeting if he had made changes to the rostering department, O'Leary said that it was "not the time to be taking people out and shooting them."
Hickey joined Ryanair as an engineer in 1988 when the airline was far from the dominant carrier it is today and became Director of Engineering in 2000 before taking over as Chief Operations Officer three years ago.
Ryanair said it would start the process of identifying and recruiting a successor and that Hickey would hand over his responsibilities over the next 3 weeks.
After the cancellations sparked customer outrage and a wave of negative media coverage across Europe, Ryanair has been scrambling to appease its pilots and promised them significant improvements in pay and conditions on Thursday.
Ryanair has said reports it had a pilot shortage were false and that less than 260 of its 4,200 pilots had left so far this year amid some being poached by rival Norwegian Air Shuttle .
In a separate statement on Friday, it said it had hired 210 new pilots in the past 12 weeks, bringing to 822 the number who have joined since the start of the year.
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