RIO DE JANEIRO, June 9 -- For a decade the Gulf's three biggest airlines turned a patch of desert into the crossroads of global aviation, routing the planet's long-haul traffic through Dubai, Doha and Abu Dhabi. This year some of them are expected to fly it at a loss.

The reason sits a few thousand miles to their north, in the oil that the war on Iran has made expensive. The International Air Transport Association, the trade body that speaks for most of the world's carriers, delivered the downgrade at its annual meeting in Rio de Janeiro, and it was a steep one. The industry is now expected to clear about $23 billion in net profit in 2026, down from the $41 billion the group had penciled in only months ago and roughly half the $45 billio...