Cat B Definition
The definitions of Cat B are fully defined in the airworthiness requirements which are CS/FAR 29 for large helicopters.
There are two types of Cat B envelopes (CS29/FAR29); one for helicopters with 9 or less passenger seats and one for more than 9 passenger seats.
Basic AW139 RFM provides the Cat B envelope for the more than 9 passenger seats configuration while Supplement 51 covers the 9 or less passenger seats configuration.
In the Basic RFM configuration the Cat B envelope provides assurance that for any take off/landing carried out outside of the H-V envelope within the maximum weight defined by the WAT charts a safe reject can be succesfully achieved after an engine failure provided this happens over a flat and prepared surface and up/from 50 ft height of the profile. Furthermore a climb capability at OEI CONTINOUOS rating is assured if the Vy is achieved. There is a undetermined portion of the take off profile from the climb out speed (50 KIAS) at 50 ft up to Vy where the regulation does not require a safe OEI capability (nonetheless the 139 is still capable in most of its envelope). The 139 in this Cat B enevlope guarantes also the in ground effect low speed controllability up to 40 kts from all directions.
The other Cat B envelope, that is included in Supplement B, there are no limitations (as per regulation requirements) other than the HIGE performance for take off and landings. Climb out or rejects are not required to be demonstarted although also in a considerable part of this envelope the 139 has such capabilities (providing a suitable surface is available for rejects).