The Economist investigates:
Averaged over the past four decades, the net profit margin of the world’s airlines, taken together, has been a measly 0.1%. By contrast, other bits of the travel business that depend on the airlines—such as aircraft-makers, travel agents, airports, caterers and maintenance firms—have done very nicely.
The airlines aren't without blame:
The airlines’ chronic unprofitability is partly the result of a wave of competition—especially from new low-cost carriers—unleashed by the steady deregulation of aviation since the 1970s. But it is also due to two moves by the airlines, from the 1990s onwards, that in retrospect were strategic errors. One was to stop paying direct commissions to travel agents. The other was to set the reservation systems free to become (as the airlines see it) profit-gobbling monsters that devour their parents.
The Dish 