The chief executive and co-founder of Norwegian Air Shuttle, Bjørn Kjos, has stepped down after 17 years in charge at the airline.

Under the leadership of Mr Kjos, aged 72, Norwegian Air developed from a small domestic airline into Europe's third biggest low-cost carrier.

It also broke into the transatlantic market with low fares.

However, the firm has struggled to make profits and has also been hit by the grounding of the Boeing 737 Max plane.

Norwegian has 18 of the aircraft and on Thursday said that it did not expect them to return to service until October, later than its previous estimate of August.

The airline said the grounding could cost as much as 700m Norwegian kroner (£65m; $82m) this year, and could also undo its plan to return to profitability.

The 737 Max fleet of jets was grounded after two crashes, the first a Lion Air flight which crashed into the sea off Jakarta last year, and the second an Ethiopian Airlines' flight which crashed shortly after take off from Addis Ababa in March. In total 346 people were killed.

Norwegian's low fares have allowed it to grow rapidly. Last year it launched 35 new routes, carried more than 37 million passengers and added 2,000 staff.

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Its big innovation has been to operate low-cost long-haul flights between the UK and the US, which it started in 2014. It now flies to 12 US destinations from London's Gatwick airport.

It has become the biggest international carrier to serve the New York City area, carrying more passengers there than British Airways, Air Canada or Lufthansa, according to figures from the Port Authority of New York & New Jersey.

However, that growth has come at the expense of profits.

The airline lost 1.45bn kroner last year, which it blamed on fuel costs, tough competition and issues with engines on its Dreamliner aircraft.