The stock slid 4.1% to $32.04 a share. The company said in an investor update Thursday it now expects fourth-quarter revenue to rise 1.5% year over year, which is at the lower end of the 1.5% to 3.5% forecast.
"This change is due primarily to a lower than anticipated improvement over a strong fourth quarter of 2017 in the domestic market," the update said.
The airline also slightly lowered its earnings-per-share forecast. Management expects full-year 2018 EPS in a range between $4.40 and $4.60. Following its third-quarter earnings, American Airlines said it was expecting a range of $4.50 to $5.00.
American's warning came not long after Delta Airlines Inc. (DAL) - Get Report also revised its outlook for the fourth quarter. Delta said earlier this month it now expects quarterly revenue to rise 3% from a year earlier, rather than initial expectations of a 3.5% increase.