A two-month, $3.3 million repair project began Wednesday at Leesburg Executive Airport that will include resurfacing the 5,500-foot runway, fixing a sag at the north end and installing brighter lights.

"It's a necessary facelift," said Cindi Martin, the airport's director. "It [the runway] has passed its useful life and was beginning to disintegrate."

Leesburg is the second-busiest general aviation airport in Virginia, averaging about 90,000 takeoffs and landings a year. It is a reliever airport for Dulles International Airport and is home to Piedmont Hawthorne's American Beechcraft Service Center, which provides maintenance services and sells fuel and airplanes; a Federal Aviation Administration Flight Service Station that provides weather and advisory information; several flight schools; and more than 200 private aircraft.

During the repairs, flights will be limited to daylight hours and conditions with good visibility, instead of 24 hours a day and most weather conditions. Jets, turbo props and large twin-engine planes will not be allowed. Air ambulance services will not be affected, but some other helicopter services will be restricted at night.

Stephen Axeman, chairman of the Leesburg Airport Commission, said he expected at least a 20 percent reduction in flights during the repairs but said the work is necessary as a safety measure and to ensure that the airport makes a long-term economic contribution to the region. The airport contributes an estimated $40 million a year to the local economy, most of which benefits Loudoun County, Axeman said.

"If you don't have a runway, you don't have an airport," Axeman said. "And larger jets aren't going to want to come into a runway that's crumbling. . . . You can see there's cracks all over the place. I don't think it would have made it another year."

Martin said the runway, which has a lifespan of about 15 years, was last replaced in the early 1990s, when it was widened to 100 feet and lengthened. She said the crown, a high point that is supposed to run along the center line of the runway to allow water to drain, was not moved when the runway was widened and must be recentered.

Work has been scheduled so it will interfere with as few flights as possible. Repairs will be made on the southern 2,750 feet of the runway until the end of June, at which point that portion will be reopened and work will begin on the northern half. The entire runway is expected to be closed for about two days in August so grooves can be carved into the pavement to help prevent planes from skidding in wet conditions.

The Federal Aviation Administration is paying 95 percent of the project's cost. The Virginia Department of Aviation will cover 4 percent and the town of Leesburg the rest, about $33,000. Funds were included in the 2005 budget.

An instrument landing system, which will give pilots more precise guidance as they descend, is scheduled to be installed in June 2006.