(CNN) - The chief executive of one of Europe's largest low-cost carriers stepped down Thursday from the company he founded and still partially owns.
Norwegian Air's Bjoern Kjos said that he would continue working as an adviser to the airline's chairman, focused on industry alliances and building on a recent agreement with rival EasyJet.
Chief Financial Officer Geir Karlsen will act as interim CEO while the company hires a permanent replacement.
Norwegian Air shook up global aviation by offering discounted flights within Europe and to the United States, Asia, and Latin America. Kjos owns part of a 17% stake in the carrier through a holding company under his control.
The company's future has been called into question after a rapid expansion left it in debt. In January, it sought to raise 3 billion Norwegian kroner ($352 million) to shore up finances.
Analysts say the departure of Kjos, a former fighter pilot who led the company for 17 years, could remove a roadblock to a possible sale to a larger aviation group. It previously rebuffed offers from British Airways owner IAG.
"Bjoern has been the driving force behind the business — the big question now is whether [Norwegian Air] can maintain momentum as he takes a less active role," said analysts at research firm Bernstein.
Shares in the company dropped more than 7% in Oslo after it announced Kjos' departure and reported earnings for the second quarter. Revenue and profit both topped analyst expectations.
Norwegian Air was founded in 1993 as a small regional airline in Scandinavia, but it now flies Boeing Dreamliner aircraft from bases in Barcelona, Copenhagen, London, Paris, Rome and Stockholm to some of the main tourist and business destinations in the United States.
The company was forced to cut several routes after the Ethiopian Airlines disaster led to a global grounding of Boeing 737 Max 8 jets, of which Norwegian Air was a launch customer.
Norwegian Air is seeking compensation from Boeing. It said Thursday that the grounding will cost it 700 million Norwegian kroner ($82 million) in 2019.
The European aviation industry has had a tough time recently. Icelandic budget carrier Wow Air ceased operations in March, following the demise of Germania and British airline Flybmi a month earlier.