Malaysia Airlines Berhad (MAB) chief executive Christoph Mueller has resigned, a year after taking up the post to revamp the beleaguered airline.

The 54-year-old German, who is also the airline's managing director, is stepping down "due to his changing personal circumstances", said the airline in a statement yesterday.

The national carrier has started searching for a replacement both internally and externally, while Mr Mueller serves a six-month notice period until September. He remains a non-executive director on MAB's board.

"Unfortunately, personal circumstances will make it difficult for me to complete my full term," Mr Mueller said in the airline's statement, without elaborating.

He had previously turned around Ireland's Aer Lingus and was brought in by MAB on a three-year contract, as part of the carrier's restructuring exercise to lift it from the red and revamp its image following two plane disasters in 2014.

He joined the airline's board in January last year, became CEO-designate in March and officially took over from previous chief Ahmad Jauhari Yahya on May 1 the same year.

The airline's chief operations officer Peter Bellew has been appointed as executive director with immediate effect.

Sovereign wealth fund Khazanah Nasional, sole owner of MAB, said in a separate statement that it would undertake succession planning for the airline's new chief executive through consultation with MAB's board and the finance ministry.

The fund also said that the airline's recovery plan is "on track".

MAB was known as Malaysia Airlines Systems Berhad (MAS) before the major restructuring started in August 2014, with the airline delisted from the local stock exchange in December 2014, appointment of new senior management and 6,000 jobs axed.