By John S. McClenahen Apparently a slowing U.S. economy is not going to ground business jets and other general aviation aircraft. With a substantial backlog of orders and new business jets slated to roll out this year, "2001 will be another good year for general aviation," predicts Mike Smith, chairman of the General Aviation Manufacturers Assn., Washington. Last year was a very good year for the industry. General aviation billings in 2000 reached a record $8.6 billion, up 9.1% from 1999's $7.8 billion. Manufacturers' shipments increased 12.5% to 2,816 airplanes -- 1,913 piston-powered aircraft, 315 turboprops, and 588 turbofans.