The category-defining specification is, in the end, the fuselage width. ICAO defines ten airport categories and specifies the minimum amount of water, dry chemical powders (or “other complementary agents having equivalent fire fighting capability”) and discharge rates of the crash tenders for each case.

Cat 1: 0m < L ≤ 9m, fuselage Ø < 2m Cat 2: 9m < L ≤ 12m, fuselage Ø < 2m Cat 3: 12m < L ≤ 18m, fuselage Ø < 3m Cat 4: 18m < L ≤ 24m, fuselage Ø < 4m Cat 5: 24m < L ≤ 28m, fuselage Ø < 4m Cat 6: 28m < L ≤ 39m, fuselage Ø < 5m Cat 7: 39m < L ≤ 49m, fuselage Ø < 5m Cat 8: 49m < L ≤ 61m, fuselage Ø < 7m Cat 9: 61m < L ≤ 76m, fuselage Ø < 7m Cat 10: 76m < L ≤ 90m, fuselage Ø < 8m

Index A includes aircraft less than 90 feet in length. Index B includes aircraft at least 90 feet but less than 126 feet in length. Index C includes aircraft at least 126 feet but less than 159 feet in length. Index D includes aircraft at least 159 feet but less than 200 feet in length.