Small aircraft употребляется в USA (FAA) федеральное Авиационное Агенство.
http://aspmhelp.faa.gov/index.php/Weight_ClassВот их классификация.
Т.е. под Small они считают Beech 90, или Cessna Caravan (до 5700 кг).
Weight Class
Weight class is based are assigned by APO130 based on the TFMS observed aircraft codes. There are 6 categories -- (A) Heavy, (B) B757, (C) Large Jet, (D) Large Commuter, (E) Medium, (F) Small.
(A) Heavy: Any aircraft weighing more than 255,000 lb such as the Boeing 747 or the Airbus A340;
(B) B757: Boeing 757 all series;
(C) Large Jet: Large jet aircraft weighing more than 41,000 and up to 255,000 lbs such as the Boeing 737 or the Airbus A320;
(D) Large Commuter: Large non-jet aircraft (such as the Aerospatiale/Alenia ATR-42 and the Saab SF 340), and small regional jets (such as the Bombardier Canadair Regional Jet), weighing more than 41,000 and up to 255,000 lbs;
(E) Medium: Small commuter aircraft including business jets weighing more than 12,500 up to 41,000 lbs such as the Embraer 120 or the Learjet 35; and
(F) Small: Small, single, or twin engine aircraft weighing 12,500 lbs or less such as the Beech 90 or the Cessna Caravan.