Delta said Thursday morning that it expects its net income for the quarter to come in between $1.25 a share and $1.30 a share. Despite that encouraging news, investors focused on a slight reduction in its revenue expectations. Specifically, Delta expects unit revenue to rise by 3% in the quarter, down from its previous forecast of 3.5%.

Unit revenue is a metric that airlines use to measure revenue against available seat capacity. In an investor update, Delta said of its unit revenue that “the pace of improvement in late December was more modest than anticipated.” In a market where investors are skittish about any hint of a slowdown in earnings, the revision triggered a selloff in airline stocks.

Delta closed Thursday down 8.9% at $45.61 a share, with other airlines also suffering stock-price declines. American Airlines Group declined 7.5%, Mesa Air fell 6.3%, Spirit Airlines dropped 6.7%, United Continental declined 5% and Alaska Air fell 5.5%.

In the past five trading days, Delta’s stock has lost nearly a quarter of its market cap.

Some analysts outlined a scenario in which Delta or other airlines face increasing competitive pressure to lower airfares amid a decline in fuel prices as well as a possible slowdown in consumer spending should an economic downturn prompt households to tighten their budgets.

“In the past, the airlines have competed away gains from lower fuel as they reward customers with lower fares,” Cowen & Co. analyst Helane Becker said in a research note. “With oil trending lower in recent months, investors are worried this time will not be different.”

Concerns about slowing revenue growth is rattling investor confidence this week. The Dow lost 660 points Thursday after Apple warned that revenue during the December quarter would come in well below Wall Street expectations. The news triggered selling in other tech stocks as well as companies that, like Apple, have some exposure to China’s slowing economy.