Process and device for determining an optimal flight path of an aircraft

A process for determining an optimal flight path (T) of an aircraft (2) during the cruising phase of said aircraft (2) from a first vertical position corresponding to an initial position (PO) at cruising altitude to a second vertical position corresponding to a terminal position (PF) at cruising altitude, said flight path (T) consisting of adjacent straight vertical path portions (PT), said method comprising:

• forming a grid (M) of the space between said first and second positions (PO, PF), said grid (M) corresponding to the division, in a vertical plane (OXY), of the space between said first and second positions (PO, PF) at cruising altitude, into N successive steps, namely steps 1, 2, . . . , k, . . . , N, N being a specified integer and k being any integer lying between 1 and N, each of said successive steps 1 to N being successively performed in order from said first position to said second position, the first position (PO) representing a step O and the second position being situated at step N, each of said N steps k being defined by a vertical line (L1 to LN) of said vertical plane (OXY), defining for each of said N steps, various positions (PkA, PkB, PkC, PkD) situated at various altitudes (A, B, C,) along the corresponding vertical line (Lk), and associating with each of said N steps k, path portions (PT1 to PT10) permitted for flight by the aircraft (2), between the positions (Pk-1A, Pk-1B, Pk-1C, Pk-1D) defined for step k-1 and the positions (PkA, PkB, PkC, PkD) defined for said step k;
• and
• repeating the following operations, relating to a step k, for each of steps 1 to N:
• a) selecting the path portions (PT1, PT2, PT4, PT5, PT7, PT8, PT10) liable to be followed by said aircraft (2) from all the path portions (PT1 to PT10) associated with step k and defined in said grid (M), on the basis of specific characteristics of the aircraft;
• b) evaluating the cost of each of said selected path portions, said cost corresponding to the value of a cost criterion relating to the traversal of said aircraft (2) of each path portion;
• c) determining various possible paths for joining up with various positions (PkA, PkB, PkC, PkD) of step k starting from the first position (PO) on the basis of the paths (Tk-1A, Tk-1B, Tk-1C, Tk-1D) retained in a previous performance of operation f) relating to step k-1 and on the basis of the path portions selected in the present performance of operation a) relating to k;
• d) computing the cost of each of said possible paths determined in the present performance of operation c) relating to k on the basis of the cost of the paths retained during a previous performance of operation f) relating to step k-1, and of the cost evaluated in the present performance of operation b) relating to k;
• e) comparing, for each of the positions of step k, the costs computed in the present performance of operation d) relating to k of the paths arriving at said position with one another;
• and
• f) retaining the path exhibiting the lowest cost, the path (T) retained for step N and arriving at said second position (PF) corresponding to said sought-after optimal flight path.