of the lateral margins which is taken on a band of larger width various examples of positions 22 to 25 are given for the index of relative height of the aircraft when the index of relative height of the aircraft is in the positions 22 or 25 the safety floor of the aircraft is above the reliefs or obstacles on the ground of the part overflown of the navigation band but certain reliefs or obstacles on the ground that are laterally close to the navigation band are above the safety floor there are therefore limitations of lateral margin of maneuver when the index of relative height of the aircraft is in the positions 23 or 24 the safety floor of the aircraft is above any relief or obstacle on the ground that are close there is therefore no limitation of the lateral margins of maneuver for the formulation of the vertical profiles 20 21 of the navigation band and of the lateral margins the terrain elevations are derived from a database of terrain elevations as a function of the plot of the trajectory scheduled in the flight plan and of the widths allowed for the navigation band 5 alone and the navigation band 5 increased by the lateral margins 9 and 10 to fix the lateral dimensions of the right and left margins 9 10 the basis therefor is an estimation of the lateral dimensions of the horizontal areas occupied by the ground trace of the trajectory traversed by the aircraft when it performs at least one half revolution flat by tightening the turn to the maximum permitted and in the presence of a local wind for this estimation one begins by establishing the parametric equations of the ground trace in the absence of local wind.