After wrangling with the U.S. Department of Transportation, the carrier last week reinstated a "Passenger Usage Fee" of $4.90 each way.

Spirit began charging the fee last summer, along with a $2.50 "natural occurrence interruption fee" and an $8.50 "international service recovery fee."

A natural occurrence is more commonly known as "weather." The recovery fee aimed to offset the costs of doing business with international destinations.

The DOT quickly slapped the fees down and levied a $40,000 fine against the carrier for misleading advertising: An airline operating in the U.S. may not advertise fares that do not include fees that are imposed on all passengers. Fuel surcharges are the most common example.

Spirit does not intend to reinstate the natural occurrence and international service fees.

However, it tweaked the presentation of the Passenger Usage Fee on its Web site so that it is included in the "Total departure air fare per passenger including all taxes and fees" amount and is explained in the "Quick note about taxes and fees" that appears in small print below the search results. What the note does not explain is that the fee can be avoided by purchasing the ticket at the airport counter, which is a departure from the way airlines have operated in the era of Internet travel sales.

Airlines have sought to encourage customers to book through their Web sites by tacking on fees for call center bookings and airport ticket counter bookings. The fees are justified, they say, because human intervention adds to labor costs. Spirit, however, is waiving the fee for what is probably its most expensive method of distribution. The fact that it also is its least convenient means of distribution for the passenger may be a factor.

Spirit is not the first airline to try to offset distribution costs through the introduction of fees. Allegiant Air assesses a "convenience fee" of $13.50 per passenger for bookings on its Web site. It charges an additional $10.00 per segment for call center bookings. Fees are not charged for airport ticket counter bookings.

Ryanair, meanwhile, charges a "payment handling fee" of £4.75 or €5 per passenger per one-way flight, whether the booking is made online, through a call center or at the airport.