An embodiment includes an apparatus that supports a user to make planning decisions of fuel efficiency of an aircraft versus time of arrival of the aircraft along a flight path. An embodiment of the apparatus accepts input data related to the aircraft. The input data may include (i) flight plan data that includes a flight path of the aircraft, (ii) state of the aircraft along the flight path, (iii) environmental data, and (iv) an aircraft performance model of the aircraft. The apparatus calculates aircraft performance and an objective function for a range of altitudes and speeds as a function of the input data. The apparatus causes a user interface to display aircraft performance contour boundaries and a vertical routing path that meets the objective function to provide graphical representations to support a user's planning decisions.