DAYTON — Passenger boardings at Dayton International Airport declined by 6 percent in April from the same month a year ago, but the airport’s top manager said he expects an overall increase for all of 2011.

“I don’t think it’s a trend,” Terrence G. Slaybaugh, Dayton’s director of aviation, said Wednesday.

The airport’s passenger traffic showed increases of 9 percent in January from a year earlier, 3 percent in February and 2 percent in March. Last year, passenger traffic dropped in March but ended with a 1 percent total increase for 2010.

Airline changes in the number and sizes of planes flown in any given month can cause such fluctuations, Slaybaugh said.

The Dayton airport’s boardings in April totaled 102,010, down from 108,545 a year earlier. But, boardings for the year to date have increased by 1.4 percent to 382,051, up from 376,929.