In the context of helicopter aerodynamics, the statement about rotor disc loading in a horizontal curve refers to the forces experienced by the rotor blades when the helicopter banks to make a turn. Rotor disc loading is defined as the total weight supported by the helicopter's rotor system divided by the area of the rotor disc.

The correct statement is, it increases with increasing bank angle.

This is correct because when a helicopter banks to enter a horizontal turn, the lift generated by the rotor system must not only support the weight of the helicopter but also provide the centripetal force necessary to execute the turn. As the bank angle increases, the portion of lift directed towards counteracting gravity (supporting the weight) decreases, while the portion directed towards producing the centripetal force increases. To maintain altitude and turn effectively, the helicopter's rotor system must generate additional lift, thereby increasing the rotor disc loading.

To put it simply, a higher bank angle during a turn requires more lift from the rotor system, leading to increased rotor disc loading.