Southwest ( LUV) says its traffic has continued to slow in March. "We saw things weaken sequentially in February," CEO Gary Kelly said Tuesday, at the JPMorgan Aviation and Transportation Conference in New York. "It appears that the first week of March is weaker still than what we had in February." Passenger revenue per available seat mile fell about 7% in the first week of March, said Kelly, adding that the trend could worsen because Easter will occur in April this year after falling in March 2008. "I don't see that we're stable on the revenue front at this point," he said. "I don't know that we've reached a bottom." Both Kelly and Continental ( CAL) President Jeff Smisek said business traffic, as discerned by close-in bookings, is slowing more precipitously than leisure traffic. "Leisure bookings have held up much better than business bookings," Smisek said. In particularly, business travel across the Atlantic has fallen, he said.