ByJohn S. McClenahen Total billings for the U.S. general aviation industry, driven by record shipments of business jets in the U.S. and abroad, reached a record high of $4.4 billion during the first half of this year, reports the Washington-based General Aviation Manufacturers Assn. The figure was 2.8% better than the $4.3 billion in billings recorded in the first six months of 2000. Some 303 business jets were shipped between January and June this year, 5.2% more than during the first half of 2000. Turboprop shipments matched last year's first-half figure of 165. However, shipments of piston-driven aircraft fell 5.6% to 816 units, resulting in a 2.5% decline to 1,284 in the total number of general aviation airplanes shipped during the first six months of 2001.