Lufthansa appointed Christoph Franz, the head of its Swiss unit, as deputy CEO, backing up chief executive Wolfgang Mayrhuber.

Franz, 48, would also oversee the company's main business, passenger airlines, Lufthansa said in a statement on Thursday.

German media have speculated that Franz is a leading candidate to succeed Mayrhuber, who retires next year at age 63.

Franz, a former executive at Deutsche Bahn, has been with Swiss since 2004, a year before Lufthansa bought the company in the biggest airline merger since Air France took over KLM Royal Dutch Airlines.

His appointment, effective from June 1, expands the management board to four from three members. It now comprises Mayrhuber, Chief Financial Officer Stephan Gemkow and Stefan Lauer, head of personnel.

Lufthansa also said its supervisory board would decide the extension of Lauer's contract for a further five years as early as legally possible.