Travelers should pack light because air carriers in the United States will be operating planes filled to capacity during the Thanksgiving holiday, the Air Transport Association of America said Monday.

But don’t let the full planes fool you, the ATA said. Planes will be fully loaded because airlines, including Dallas-based Southwest Airlines Co. and Fort Worth-based American Airlines, have been cutting capacity —or the number of flights offered on certain routes — to deal with falling demand in a lackluster economy.

Therefore, full planes do not indicate higher traffic. In fact, the ATA said air travel this Thanksgiving holiday season is expected to be down 4 percent when compared with last year.

The busiest travel days will occur on Nov. 20, Nov. 25 and Nov. 29-30, the ATA said.