Nov. 9 (Bloomberg) -- U.S. airline travel will decline 4 percent during the 12-day Thanksgiving holiday period this month as the slow economy discourages passengers from buying tickets, the carriers’ trade group said today.

Economic headwinds “are anything but behind us” and unemployment surpassing 10 percent is “one of the key factors” that affects consumer purchasing, James May, president of the Air Transport Association trade group in Washington, said in a statement.

The group, with members including Delta Air Lines Inc. and AMR Corp.’s American Airlines, said the holiday travel period will run from Nov. 20 through Dec. 1. The busiest day will be Nov. 30, followed by Nov. 29, 20, and 25, the trade group said.

U.S. airlines this year have been cutting the number of seats they offer for sale by the most since 1942 as travel demand has slumped during the U.S. recession, the group said. Holiday flights will likely be “quite full” due to the capacity cuts and fare discounting, the association said.

A year ago the Air Transport Association projected a 10 percent year-over-year decline for the 2008 Thanksgiving holiday period.

U.S. airlines’ on-time arrival rate in September was the highest in six years, as the number of scheduled flights fell to the fewest for the month since 2002, the Transportation Department reported earlier today.

The department tracked almost 511,000 airline flights in September, down from about 541,000 in the same month the previous year. In September 2002 there were 430,000.

To contact the reporter on this story: John Hughes in Washington at jhughes5@bloomberg.net

Last Updated: November 9, 2009 15:17 EST