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A more predictable Air Traffic Management (ATM) system based on automation requires a precise Trajectory Computation Infrastructure (TCI). The accuracy of the computed trajectories does not only depend on the TCI trajectory integration capabilities, but also on the input received from the associated Aircraft Performance Model (APM), the operational instructions defining each trajectory, and the atmospheric data. EUROCONTROL Experimental Centre (EEC) conducts a number of activities in the domain of APMs, which are performed within the scope of Base of Aircraft Data (BADA). EEC has been supported by Boeing Research & Technology Europe (BR&TE) in the definition, development, implementation, and evaluation of an advanced APM suitable for the stringent requirements of future trajectory prediction tools. This new APM will become version 4.0 of BADA, released and maintained by EEC. BR&TE has also supported EEC in the design and development of an advanced bidimensional (vertical plane) TCI intended to exploit all the BADA 4.0 APM capabilities. This TCI accepts either a BADA 4.0 or a BADA 3.x APM, together with all kinds of winds, as well as temperature and pressure deviations over the International Standard Atmosphere (ISA). The TCI requires five simultaneous operational instructions to compute any trajectory segment. These instructions model the commands issued by the flight deck, and comprise the "aircraft intent" (AI). Three of them set the position of the landing gear, high lift devices, and speed brakes, while the other two determine the aircraft motion in the vertical plane. Accepted instructions include different speed, energy, altitude, vertical speed, path angle, and throttle laws, and even optimum speed laws intended to maximize certain flight characteristics, such as range or cost. This paper presents the TCI capabilities and interfaces. It describes the different elements involved in the trajectory computation process, placing special emphasis in - the instructions comprising the AI and how they can be combined, as well as the equations describing the aircraft motion and their integration. It also includes an example of the trajectory computation process.