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* Simone Menne to join unlisted Boehringer Ingelheim as CFO
* Lufthansa shares down 5.5 pct, biggest Dax faller (Recasts, adds details, shares, analyst comment)
FRANKFURT, June 10 (Reuters) - The chief financial officerof airline Lufthansa, Simone Menne, will joinGermany's second-largest drugmaker Boehringer Ingelheim inSeptember, her departure knocking shares in the carrier onFriday.
Lufthansa announced late on Thursday the well-regarded Mennewas leaving from Aug. 31 and Boehringer said on Friday she wouldjoin the family-run company as CFO on Sept 1.
Shares in the carrier fell 5.5 percent to their lowest sinceSept 2015, making it the biggest faller on the German blue-chipindex as investors worried the company's cost-cuttingplans could be thrown off course.
Her departure comes at a time when Lufthansa is grapplingwith cost challenges, notably on the labour front, and expandingbudget unit Eurowings to offer cheaper tickets and defend routesagainst the likes of Ryanair and easyJet.
CFO for the last four years, Menne has maintainedLufthansa's investment grade credit rating, helped steer thegroup to record profit and last month she said the group hadreached a turning point on bringing down unit costs excludingthe price of fuel and currency.
However, the group still needs to strike wide-ranging dealswith pilots and cabin crew over pay and conditions, disputesthat have seen a series of strikes over the last two years.
Credit Suisse analysts said her departure would deal a blowto the confidence in the airline's cost-cutting efforts, alsohighlighting how Lufthansa has seen other top executives departduring periods of restructuring, such as former CEO ChristophFranz to Roche in 2013 and CFO Stephan Gemkow to Haniel in 2012.
Gerald Khoo at Liberum said however, her departure wasunlikely to impact cost saving plans in the short term, and thata new CFO should be in place in due course.
"Lufthansa does have strength in depth, assuming it does notgo for an external candidate as replacement," he told Reuters.
Analysts also cited weak May traffic figures from Thursdayas a concern for the carrier, with passenger traffic down 2percent and its planes less full.
Menne, the first female CFO at a German blue-chip companyand who had been with Lufthansa since 1989, has previouslyspoken of her ambition to become chief executive of a Dax 30company.
At unlisted Boehringer, she will succeed CFO Hubertus vonBaumbach, a member of Boehringer's founding family and who willtake over as the group's chief executive in July. (Reporting by Victoria Bryan and Ludwig Burger; Editing by ArnoSchuetze and David Evans)
