ATP Flight School, headquartered in Jacksonville, Florida, is the largest flight training company in the United States. The privately held company was founded in 1984 in Atlanta, GA by its current management, a small group of airline pilots. ATP’s initial focus was providing flight training to U.S. military pilots who were seeking their Airline Transport Pilot Certificates to transition over to commercial air carrier operations.
Maintaining a focus on professional flight training, ATP later expanded its course offerings to include ab-initio training programs for domestic students seeking a career in commercial aviation. Today, ATP is the leading supplier of professionally trained pilots to the nation's regional airlines.
ATP Flight School has the largest multi-engine training fleet in the world, consisting exclusively of Piper Seminoles, with the exception of one Cessna CE-525 CitationJet. A mix of Piper Archers and Cessna CE-172 Skyhawks make up their single-engine fleet, the majority going to the latter.
According to en.wikipedia