With over 25 years' experience as a turnaround specialist in the aviation, logistic and tourism industry, Mueller has been widely credited with leading the financial recovery of Aer Lingus.
From 1991 to 1994 he was a financial controller with Daimler-Benz Aerospace where he implemented restructuring programmes in the subsidiaries Elbe Flugzeugwerke, Dresden, Dornier and Fokker in Amsterdam.
Mueller raised funds and founded Brussels Airlines, which started operations a day after the grounding of Sabena, where he remained chairman until 2002.
[citation needed] He later served as the chief financial officer of DHL Worldwide where he was responsible for the successful turnaround programme which led to an improved bottom line of US$300 million within a year.
[citation needed] He has served as a Non Executive Director in multiple companies amongst others, LOT, Luxair, Lauda Air, Tuifly and Hapag-Lloyd Shipping.