SANTA ROSA -- The number of passengers flying in and out of Charles M. Schulz--Sonoma County Airport climbed 7.7 percent in March this year from February but dropped slightly compared with a year before, according airport figures released today.

In March, a total of 16,158 passengers used the airport, up from February's total of 14,996. In March 2011, 16,370 passengers were counted, for a decrease of 1.3 percent over the year.

But through March of this year,  passenger volume reached 45,834, up 2 percent from the first quarter of 2011 to an all-time high,  according to the airport.

The figures come from Alaska Airlines, the airport's only  carrier, which operates five flights a day to Los Angeles, Las Vegas, Portland and Seattle through subsidiary Horizon Air.

Earlier this year, the airline announced it would add flights to San Diego while discontinuing the Las Vegas route, saying at the time that the route was not profitable enough to continue.

The airport is also awaiting federal approval for an $84 million upgrade and expansion that would increase its capacity and allow larger jets to land and depart from Santa Rosa. The Sonoma County Board of Supervisors unanimously approved the project earlier this year.