In recent decades, the helicopter has become a safe and suitable solution for future traffic, both in congested megacities and in isolated places as well as in mountainous environment where the terrain can be dangerous. Adding the third dimension to multimodal urban transport networks will improve the way we live. In order to solve the challenge of navigation towards more autonomy, it is necessary, during mission planning and flight execution, to generate effective, accurate and feasible paths. However, the major works in the literature do not address the effectiveness - flyability and controllability - of the generated trajectories for helicopters. This paper proposes an approach with continuous-curvature trajectory generation into inclined planes and proves the controllability by a simulated autopilot system designed for an Airbus Helicopters model in Matlab Simulink environment. We found that this type of trajectories is effective and controllable by an autopilot with only 3% of deviation error. The results are promising and the approach will be integrated in our works on a 4-dimensional flight management system for helicopters.