The significance of 4D trajectory planning in Flight Management Systems (FMS) is paramount, especially with the advent of Trajectory Based Operations, which necessitate compliance with Required Time of Arrival (RTA) constraints. Despite extensive research into the generation and optimization of 4D trajectories, few studies have addressed trajectory generation under simultaneous RTA restrictions and altitude-speed restrictions along the route. To tackle this issue, this paper introduces a modular framework with a specially designed RTA adjust module. The framework initially assesses the feasibility of multiple RTA-waypoints using time windows and subsequently adjusts speeds along the flight plan to meet these RTA restrictions. Simulation results confirm that the generated trajectories meet these multiple restrictions, demonstrating the framework’s efficacy for trajectory prediction in FMS.