Classification of attack helicopters are not done on the basis of empty weight only. Classification of attack helicopters are based on certain guidelines provided by aviation controlling authorities just like commercial helicopters. Like FAA(Federal Aviation Administration) of USA has one classification criteria while other aviation administration of other countries have other own scales. Attack helicopters are classified on the basis of Empty weight + weight of crew + Certain fixed payload. Take an example of commercial or passenger helicopters:
Type-I (Heavy) - Skycrane / S-61 / 214ST
Type-II (Medium) - Bell 205
Type-III (Light) - Jetranger / Md-500
Helicopter Classification per USFS:
ICS-type I:
700 gal water, 16 seats including the pilot, allowable payload 5000 lbs. (e.g.: Boeing-234, S-64, AS-332, Vertol-107)
ICS-type II:
300 gal water, 10 seats including the pilot, allowable payload 2500 lbs. (e.g.: Bell-212, Bell-205, BK-117, S-58)
ICS-type III:
100 gal water, 5 seats including the pilot, allowable payload 1200 lbs. (e.g.: Bell-206B-III, Lama, MD-500, AS-355)
ICS-type IV:
75 gal water, 3 seats including the pilot, allowable payload 600 lbs. (e.g.: Bell-47, Hiller-12E)
