By now investors should know better than to put their money in US airlines. Over almost any given long-run period, the sector underperforms the broader indices as the world finds new ways to crush industry hopes. Late last year, falling oil prices suggested bumper profits in 2009, until the depth of the recession put paid to that notion. Yet the listed airline sector has again been caught in a gust of optimism, rallying 75 per cent from its February lows. Positive sentiment alone is unlikely to keep it aloft.

There is little other impetus for the rally. Since it began, earnings expectations have collapsed. Next year’s forecast for Southwest, the largest carrier by revenues, has halved. Predictions that United Airlines would be profitable this year have shifted to a loss of almost $10 a share, while the analyst consensus for 2010 has been slashed from $5 per share to less than $2. Fuel prices, meanwhile, have been steadily rising.