Method for assisting low altitude navigation of an aircraft

A method of assisting low-altitude navigation of an aircraft equipped with a flight management system suited to determining a flight-plan ground trajectory for the aircraft based on a sequence of straight and/or curved segments joining intermediate points on the ground P at an altitude alt(P), where the ground trajectory takes into consideration the aircraft's performance and limitations, comprising the following steps:

• for each point P on the ground trajectory, calculating a safe altitude, alt safe, to obtain a point Psafe such that alt safe (Psafe)=Max[alt(P+lat mrg R), alt(P+lat mrg L)]+vert mrg, where lat mrg R and lat mrg L are respectively predetermined right and left lateral margins and vert mrg is a predetermined vertical margin,
• calculating a safe profile formed from safe segments joining the points Psafe,
• extracting summit points S from among the points Psafe of the safe profile such that the K points located before S and after S have a safe altitude below that of S, K being a determined parameter,
• determining the aircraft's weight at these points S as a function of the distance along the safe profile between the aircraft and this point S and of the aircraft's consumption over this distance, where the consumption is an aspect of ‘the aircraft’s performance and limitations,
• for each point S, determining the maximum climb slope (MaxClimbFPA) that the aircraft can support to reach S and the maximum-descent slope (MaxDescFPA) which the aircraft can support for following the lowest ground trajectory after having passed through S as a function of the aircraft's performance and limitations and the weight, defining two performance segments which have a first end at S, slopes MaxClimbFPA and MaxDescFPA on either side of the point S and a second end at the point of intersection with the terrain or with another performance segment arising from another point S and calculating a performance profile formed from performance segments and which makes it possible to associate at each point P of the safe profile a performance altitude, alt perf (P).