Airline investors usually love a drop in fuel prices which are, after all, the industry’s single biggest cost. The International Monetary Fund just downgraded its global forecasts again. As of August, demand in the year to date was up by just 3.1%, according to Deutsche Bank estimates, setting up what could be the weakest year for growth in oil consumption there since 2005. So far, though, it has chosen to defend its market share instead, and seems to be banking on lower oil prices forcing some higher-cost rivals offline instead.