Process for displaying flying aid symbols on a screen on board an aircraft

Process for the display of flying aid symbols on a screen (EV) on board an aircraft, for traversing a flight path formed by successive approach segments (S1 to S4), a final segment (S5) and a rounding off segment traversed up to the touchdown point (F) of the aircraft wheels on a runway (P) comprising:

• defining a fixed reference mark frame (O, Xt, Yt, Zt) linked with the runway and having orthogonal axes, having for its origin a theoretical wheel touchdown point on the runway, said point being located on a longitudinal axis of the runway, the fixed reference frame having a first axis (Xt) coinciding with the longitudinal axis of the runway, a second axis (Yt) perpendicular to the first axis in a plane of the runway and a third axis (Zt) perpendicular to the first and second axes of the fixed reference mark frame;
• defining a mobile reference mark frame (G, X.sub.A, Y.sub.A Z.sub.A) linked with the aircraft and having for its origin the center of gravity (G) of the aircraft and a first axis (X.sub.A) coinciding with a longitudinal axis of the aircraft, a second axis (Y.sub.A) perpendicular to a plane of symmetry of the aircraft and passing through the longitudinal axis and a third axis (Z.sub.A) perpendicular to the first and second axes of the mobile reference mark frame;
• recording in a memory of on board computer, reference coordinates of the essential points of the segments of the flight path (S1 to S5, PR) measured in the fixed reference mark frame (Co, Xt, Yt, Zt);
• determining on the basis of information received from an inertial system, the coordinates of the effective positions of the aircraft relative to the fixed reference mark frame, during the traversing of the flight path, as well as values respectively corresponding to the roll (.phi.), attitude (.theta.) and bearing (.psi.) angles or Eulerian angles of the aircraft, and the orientations of a speed vector (V) of the aircraft, measured in the mobile reference mark frame;
• displaying on said screen (EV) during the traversing of the flight path, an image obtained in a plane perpendicular to the first axis (X.sub.A) of the aircraft, in the vicinity of its center of gravity (G) following a processing of the values of the Eulerian angles, of the effective coordinates, of the reference coordinates and the orientations of the speed vector, said image comprising at least:
• two identical fixed symbols (A1, A2) representing the aircraft wings, aligned on a first axis (Y.sub.E) of the screen, parallel to the second axis (Y.sub.A) of the mobile reference frame and passing through a central point (O') of the screen,
• a symbol (CP) representing a model of the aircraft indicating the orientation of the longitudinal axis of the aircraft and moving along the first axis of the screen, between the two fixed symbols representing the wings of the aircraft,
• a line (H) moving in translation and in inclination, called the artificial horizon, subdividing the screen (EV) into an upper part (H1) representing the sky and a lower part (H2) representing the ground, and making it possible to reference with respect to the fixed symbols representing the aircraft wings, the roll (.phi.) and attitude (.theta.) pitch angles of the aircraft during passage, said line being graduated so as to form a heading scale and for indicating the bearing (.psi.) of the aircraft, a symbol (V) indicating the orientation of the speed vector of the aircraft and mobile along said orientation, along a second axis (Z.sub.E) of the screen (EV) and passing through the central point (O') and perpendicular to the first axis (YE) of the screen,
• characterized in that it also comprises displaying in accordance with a three-dimensional representation, approach segments (S1 to S5) located on the flight path to be covered by the aircraft, the segment being traversed, as well as at least the segment following that being traversed, being respectively displayed in accordance with two elongated parallelepipeds, in perspective, having respectively segments for axes, each parallelepiped in perspective, having in the traversing direction of the corresponding segment, an entrance base (B1) into the segment and an exit base (B2) from the segment, said bases being rectangular, so that during the traversing of a segment, the entry base (B1) of a parallelepiped corresponding to said segment has a fixed dimension in the reference mark frame and the exit base (B2) an increasing dimension between a minimum dimension, when the aircraft starts to traverse this segment, and a maximum dimension equal to the dimension of the entry base (B1) with which it coincides at the end (B) of the traversing of said segment and at the start of the traversing of the following segment (S2) of the flight path, the process also consisting of displaying the final segment (S5) in the form of a pyramid (P3) in perspective and having a rectangular base (F3), with on the screen an apex corresponding to the touchdown point (PR) of the wheels on the runway, so that during the traversing of the final segment, the base (F3) of the pyramid of the final segment (S5) has a decreasing dimension during the traversing of said final segment up to the touchdown point (PR) of the wheels, each base of the parallelepiped and the base of the pyramid having sides located on the screen (EV) as a function of the values of the Eulerian angles and coordinates of the origin (G) of the mobile reference mark frame with respect to the fixed reference mark frame, the symbol indicating the orientation of the speed vector (V) having to be located in the center of the entry base (B1) of the parallelepiped (P1) in perspective, representing the segment being traversed, or in the center of the base (F3) of the pyramid (P3) representing the final segment, when the aircraft is correctly located on a segment.