In FAA Part 29 manuals, the maximum operating weight for the type of operation (Cat A or B) is expressed in the WAT curve, the weight, Altitude and Temperature that defines the max operating weight. For Cat B that is based on the basis of safe landing after engine failure, in conjunction with the H-V curve, and on the ability to demonstrate normal takeoff and landing. The Cat B WAT chart is many times identical to the HIGE hover chart, but many Bells have operating conditions where the tail rotor prevents crosswind ops and therefore becomes the limitation, instead of the main rotor performance. In those, the WAT chart shows a lower weight at some places than the HIGE chart. It can be seen as "bent lines" at perhaps 4000 feet where clearly something is reducing weight faster than normal atmospherics.
Some Bell manuals have a magic recovery of operating weight where pilots are allowed to ignore tail rotor weakness. These WAT curves for the 412 are specially marked "For operations with winds + 45 degrees of the nose". These special WAT curves allow operations where loss of yaw can occur when landing or hovering in cross winds. The normal FAR REQUIRES a cross wind capability of 17 knots for all helicopters, Bell applied for a special consideration as long as they were operating Cat B, with 9 passengers or less. The operator can attempt to work around the tail rotor's limitations by assuring themselves that they will not have a cross wind.
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