China was the first country to ground the 737 Max in March after two fatal crashes involving the jets.Read more
The International Air Transport Association cut its forecast for the industry's profits in 2019 to $35.5bn from $38bn, after $32.3 billion in 2018.
Now Reuters reports there are signs of a further downgrade when the industry body meets next month.
Alexandre de Juniac, IATA director general, told a meeting of industry officials: "I am a bit worried and I am sorry to tell you that I think we are at a turning point. The figures will be in the black but will be more difficult".
BBC Radio 4
Johan Lundgren, the chief executive of Easyjet, has been speaking to BBC Radio 4's Today Programme.
He says trading is in line with expectations - no airline expects to make a profit in the winter season - but that conditions are tougher than last year.
"It's not so much that there isn't demand out there but it is definitely a tougher trading environment," he said.
"It's partly down to the uncertainty that existed and exists around Brexit. There are macro-economic uncertainties in a number of European countries," he said.