Airlines have taken their eyes off the ball when it comes to cutting costs and may well suffer in the next economic downturn.
Speaking at Routes Europe 2018 in Bilbao, former easyJet CEO Ray Webster said costs have been rising as airlines relax thanks to the current relatively benign economic environment.
He added any future shocks, like a sharp increase in the oil price, would lead to problems in parts of the industry.
Webster said: "It is quite worrying actually. We've had a period of very good economic performance but what is there is a serious downturn with runaway fuel prices like we have had in the past.
"Airlines in general have had a very good run. They've been in a position where they have incrementally added to their costs and become less efficient. At some time in the future there's going to have to be a correction."