Shares of Spirit Airlines, long a Wall Street darling, fall on reduced profit-margin outlook

Shares of Spirit Airlines Inc. fell Wednesday after the low-fare carrier cut its forecast for third-quarter profit margin because of underpayment of fuel excise taxes going back several years.

Spirit's shares closed down $3.35, or 5.3 percent, to $60.17. Shares of other U.S. airlines fell but by smaller percentages.

The Miramar, Florida-based airline's shares were up 40 percent this year at the beginning of trading on Wednesday.

In a regulatory filing, Spirit said that it recently learned of an underpayment of federal excise taxes on some of the fuel it bought between July 2009, when it changed fuel-service providers, through August of this year.

Based on July and August results, and including an adjustment for 2014 fuel costs to include the taxes, Spirit said that third-quarter operating margin would be in the lower half of its previously expected range. The company said it will provide more details and third-quarter guidance on Oct. 15.

Spirit made the disclosure as it reported a 13.5 percent increase in traffic for September, compared with a year earlier. That wasn't enough, however, to offset an 18 percent increase in flying, so the average flight was 81.5 percent full, down from 84.7 percent a year earlier.

Spirit usually undercuts larger airlines on fares but takes in a higher percentage of its revenue from fees, such as a charge for buying a ticket online or stowing a bag in the overhead bin. It has been adding flights aggressively while most larger airlines limit their growth.