Many ICAO regs (and therefore NAA regs) use 5,700 kg (12,500lb) and 3,175 kg (7,000 lb) as a reference for the division between small, medium and large helicopters. Things such as licensing and maintenance seem to use this threshold a lot.
Thanks to TC for giving me a prod. Having carried these numbers around for so many years I should have checked before making the post - must be the Altzheimers catching up with me.
G
