Malaysia Airlines CEO Peter Bellew is leaving after just over a year in charge to return to Ryanair as chief operations officer to tackle the pilot shortages that has resulted in it cancelling more than 20,000 flights over the winter season.

The move means that Malaysia Airlines will have to appoint a third chief executive in three years as it continues to recover from two tragedies in 2014, when flight MH370 disappeared in what remains a mystery and flight MH17 was shot down over eastern Ukraine.

Malaysia Airlines said in a statement the move was "unexpected" but the airline's turnaround remained "on track and on schedule".

For Ryanair Bellew's return on Dec 1 comes as Europe's busiest airline is trying to recruit additional pilots and persuade existing pilots to stay with the offer of new, improved conditions to avoid a repeat of the cancellations.

Bellew was director of flight operations at Ryanair before he left in 2014. He joined Malaysia Airlines as chief operations officer in September 2015 and took over as chief executive in July last year.

Ryanair said that Bellew would be given a specific responsibility for managing pilots. His mission will be "to ensure that the pilot rostering failure which Ryanair suffered in early September will never be repeated," the company said in a statement.

Ryanair in all has announced the cancellation of around 20,000 flights after admitting it did not have enough standby pilots to operate a reliable schedule.

Irish stockbroker Goodbody last week said in a note that Bellew was well regarded in the industry and was "thought to have had a good relationship with the pilots when he was there."

In recent weeks pilots at Ryanair, which does not recognize any labor union, have been getting together on social media to lobby for a major overhaul of the company's employment conditions.

Bellew's decision to leave Malaysia Airlines comes just over a year after former chief executive Christoph Mueller left the airline, citing personal circumstances a year after being hired on a three-year mission to revive the state-controlled firm.

Mueller, formerly CEO of Ryanair's Irish rival Aer Lingus, later joined Emirates as its chief digital and transformation officer.

Under Bellew’s leadership Malaysia Airlines has been restructuring its fleet, while its owner, the state investment fund Khazanah, has said it plans to relist the airline's shares on the stock exchange in 2019.

"So much (management) turnover makes the attempted turnaround even more challenging," said CAPA Center for Aviation Chief Analyst Brendan Sobie.

In its statement, Malaysia Airlines said that Bellew had said publicly on Sept 27 that he was committed to the airline and that the turnaround of Malaysia Airlines would be "the greatest achievement of my life".