DALLAS (AP) — A big drop in passenger complaints is helping U.S. airlines post their best quality ratings ever, according to academics who study the industry. Consumer complaints to the government are down 15 percent even though more flights are late and more bags are being mishandled. Virgin America topped the ratings released Monday by researchers from Wichita State University and Embry-Riddle Aeronautical University. Three regional airlines ranked at the bottom. The researchers grade airlines on on-time performance, mishandled bags, bumping passengers, and complaints to the government.