A computer-implemented method of operating an aircraft, the method comprising: identifying a first speed constraint associated with a navigational reference point; identifying a second speed constraint associated with a second navigational reference point preceding the navigational reference point; determining a speed envelope region en route to the navigational reference point based at least in part on the first speed constraint, the second speed constraint and a maximum acceleration of the aircraft, wherein determining the speed envelope region comprises: determining a minimum travel time boundary for the speed envelope region between the navigational reference point and the second navigational reference point based at least in part on the first speed constraint, the second speed constraint, the maximum acceleration of the aircraft, and a maximum speed associated to the navigational segment between the navigational reference point and the second navigational reference point; and determining a maximum travel time boundary for the speed envelope region based at least in part on the first speed constraint, the second speed constraint, the maximum acceleration of the aircraft, and a minimum speed associated to the navigational segment between the navigational reference point and the second navigational reference point; wherein said minimum speed and maximum speed are determined based on the aircraft capabilities while en route to the navigational reference point; identifying a target speed en route to the navigational reference point; determining a speed profile for travel en route to the navigational reference point, within the speed envelope region, wherein the speed profile intersects the target speed within the speed envelope region and a slope of the speed profile is influenced by the target speed; and autonomously operating the aircraft in accordance with the speed profile. identifying a first speed constraint associated with a navigational reference point; identifying a second speed constraint associated with a second navigational reference point preceding the navigational reference point; determining a speed envelope region en route to the navigational reference point based at least in part on the first speed constraint, the second speed constraint and a maximum acceleration of the aircraft, wherein determining the speed envelope region comprises: determining a minimum travel time boundary for the speed envelope region between the navigational reference point and the second navigational reference point based at least in part on the first speed constraint, the second speed constraint, the maximum acceleration of the aircraft, and a maximum speed associated to the navigational segment between the navigational reference point and the second navigational reference point; and determining a maximum travel time boundary for the speed envelope region based at least in part on the first speed constraint, the second speed constraint, the maximum acceleration of the aircraft, and a minimum speed associated to the navigational segment between the navigational reference point and the second navigational reference point; wherein said minimum speed and maximum speed are determined based on the aircraft capabilities while en route to the navigational reference point; determining a minimum travel time boundary for the speed envelope region between the navigational reference point and the second navigational reference point based at least in part on the first speed constraint, the second speed constraint, the maximum acceleration of the aircraft, and a maximum speed associated to the navigational segment between the navigational reference point and the second navigational reference point; and determining a maximum travel time boundary for the speed envelope region based at least in part on the first speed constraint, the second speed constraint, the maximum acceleration of the aircraft, and a minimum speed associated to the navigational segment between the navigational reference point and the second navigational reference point; wherein said minimum speed and maximum speed are determined based on the aircraft capabilities while en route to the navigational reference point; identifying a target speed en route to the navigational reference point; determining a speed profile for travel en route to the navigational reference point, within the speed envelope region, wherein the speed profile intersects the target speed within the speed envelope region and a slope of the speed profile is influenced by the target speed; and autonomously operating the aircraft in accordance with the speed profile.