Category A and category B referred to in the RFM cover many certification requirements beyond just helicopter performance. Performance classes are concerned only with the helicopter's ability to climb, particularly in the event of an engine failure. Data from both category A and category B parts of the RFM charts are used to derive the maximum masses to meet the requirements of a particular performance class, but category and performance class are not synonymous.
Even when category A RFM data are used to calculate performance class data, operations will not necessarily be conducted within the category A operating envelope (for example, transition through the height-velocity avoid curve during takeoff and landing at helidecks).