Malaysia Airlines Bhd's chief executive officer and managing director Christoph Mueller has resigned just after one year at the helm. He has a three-year contract in place with the airline.

The airline, which made the announcement, said that Mueller was resigning due to "changing personal circumstances." It did not give any other reasons.

Mueller will serve a six-month notice period until September to facilitate an orderly transition, the airline said. He will remain with Malaysia Airlines as a non-executive director, it added.

"The board has acknowledged Mr Mueller's plan to leave ahead of time, which is due to this changing personal circumstances and has commenced a search for a new CEO, which will encompass both internal and external potential candidates," the airline said.

"We are very disappointed to lose Christoph as CEO, but we fully understand his reasons and respect his need to do this," the airlines' chairman Md Nor Yusof said in a statement. "In the meantime, the board is actively working to search for a new CEO, after which Christoph has indicated his intention to stay on as non-executive director of the board to facilitate an orderly transition."

Malaysia Airlines also announced the appointment of chief operations officer Peter Bellew as an executive director with immediate effect. Bellew was the director of flight operations at Ryanair before he took up his current post on 1 September 2015. He has held a hosts of different posts at the low-cost carrier, including director of training and recruitment flight operations, and head of sales and marketing.

The hiring of both Mueller and Bellew was part of the airlines' restructuring programme after it lost two Boeing aircraft and passengers within a matter of months in 2014. Part of the restructuring included shedding 6,000 employees.

Malaysia Airlines' MH370 which was on a routine flight from Kuala Lumpur to Beijing in March 2014 with 239 people on board disappeared and is yet to be found. Another aircraft MH17 was shot down over Ukraine in July 2014 killing all 298 on board.

Malaysia Airline's parent Khazanah Nasional Bhd, the government's investment arm, said it will undertake the succession planning for the new CEO in consultation with the airline's board, and the government, through the Minister of Finance. It said the final decision on the new CEO will be undertaken through all necessary consultations and approvals before the end of Mueller's term in September.

In a separate statement, Khazanah said that the implementation of the airline's five year 12-point recovery plan was on track and on schedule over the 20-month period since it was announced in August 2014. It also said that Mueller's departure had been discussed at a board meeting earlier on 19 April.

"While we would have wanted Mueller to continue as planned, we also respect and ultimately agree to his decision to leave ahead of the end his three-year contract, due to a change in his personal circumstances. We note that Mr Mueller has laid the groundwork, put in place a strong management team, and undertaken the necessary measures and initiatives that have produced encouraging signs of progress on Malaysia Airlines' path to recovery."

Speculation over Mueller's departure

There has been speculation over Mueller's departure in the social media. One person called Yi Wen noted that perhaps Mueller decided to leave after he realised that he could not change how the airline operated or had problems with its decision-making process.

Another person speculated that perhaps Mueller had opted to leave as there was too much politics involved in the running of the airlines. In a note to airline staff, Mueller said he was leaving due to "personal reasons which are beyond my control."

He said that the company was making very good progress and was on track with its plans. "We have delivered our financial budget for the first three months of 2016, our on-time performance is increasing and very stable and our customer service index is recovering with more significant improvements in the pipeline."

He said the airline has "already seen a profit in February and we are also ahead of budget which gives a strong indication that our turnaround initiatives are pulling through faster than expected." He also expressed sadness at having to leave "when we see the first pay back of the hard work of the team."