Delta had predicted a month ago that the figure — revenue for each seat flown one mile — would rise by between 2 percent and 4 percent for the key July-through-September quarter, but on Wednesday it lowered the outlook to between 2 percent and 3 percent. The statistic typically rises when an airline fills more seats, charges higher average fares, or both.
The airline said the revenue figure would have increased by 3 percent last month but was held down by "events in Russia, the Middle East and Africa," an apparent reference to fighting between Ukraine and rebels backed by Russia, violence in the Middle East, and an Ebola outbreak in Africa.
Delta also slightly increased its forecast for third-quarter fuel expense.
Within minutes of Wednesday's opening bell, Delta shares had fallen by $1.73, or 4.2 percent, to $39.20. They started the day up 49 percent so far in 2014.
Delta was able to pack a few more passengers on U.S. flights. Overall, the average flight in August was 87.6 percent full, up from 87.3 percent in August 2013 despite a few more empty seats on international flights. Since some early-morning and late-night flights rarely sell out, that probably means that many peak flights were full or even oversold.
Delta, the third-largest airline operator, said passengers flew 20.03 billion miles last month, up 3.1 percent from August 2013. Domestic traffic rose 3.8 percent while international travel increased 2.1 percent.
The airline raised passenger-carrying capacity by 2.7 percent. Airlines usually increase capacity by adding flights or using bigger planes.
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