EMMITSBURG, Md. (AP) — The skies were empty at a charity air show after participants were escorted out of the area by F-16 fighter jets sent up because President Bush was in town.

The president's security no-fly air zone was extended Sunday and included the Hagerstown event, but at least four pilots of antique airplanes who were supposed to join the charity show were apparently unaware of the Federal Aviation Administration restrictions. They were intercepted by F-16s and escorted out of the area, federal officials said.

Bush was speaking at the National Fallen Firefighters Memorial in Emmitsburg, about 26 miles from Hagerstown.

Several pilots headed to the benefit for the Experimental Aircraft Association and the Hagerstown Aviation Museum apparently were unaware of the security measure in part because their antique planes carried no radios.

A dozen planes flew into the area, causing the North American Aerospace Defense Command to scramble its fighters.