To safely and efficiently accommodate the air traffic growth in the coming years, a new concept of a time window (TW) flight has been recently proposed. A TW is a period of time during which the aircraft is required to arrive at a waypoint in the flight trajectory. It is characterised by an opening time, which represents the earliest possible time to cross the waypoint, and by a closing time, which represents the latest possible time to cross the same waypoint. Any delay from the TW in crossing the waypoint is as much a distortion of the trajectory as a change in horizontal position. The width of the TW indicates the amount of flexibility that airlines have during flight execution, as aircraft have to remain within the TW to avoid potential demand and capacity imbalances in sectors. The larger the TW width, the more flexibility a flight has. TW flights allow for flexibility in operations, through the TW width, while simultaneously maintaining predictability. The flight schedules increase traffic predictability as they are developed in the strategic (months before the day of operation) and pre-tactical (seven to one day before operation) flight planning levels. Therefore, they facilitate the development of flight schedules that satisfy demand and capacity imbalances in the air traffic network early in the planning process and provide a common view of the air traffic environment on the day of operation. This research tackled the challenge of evaluating the impact of the TW concept of operations on individual flight performance during the tactical phase (day of operation) of air traffic flow management. The flight time and fuel consumption needed to adhere to the TWs are under consideration. For the tactical assessment, a control model based on speed adjustments that allow aircraft to track contiguous TWs placed at critical waypoints along the trajectory was proposed.