Navigation assistance method for monitoring navigation performance in linear or angular mode

A method for assisting in the navigation of an aircraft navigation, the method comprising:

• calculating and displaying a linear deviation, expressed by a lateral component and a vertical component, for an aircraft in an approach phase towards an arrival airport on a first section, called a linear section, the linear deviation representing a distance separating an estimated position of the aircraft and a desired position on a target trajectory;
• calculating and displaying an angular deviation, expressed by a lateral component and a vertical component, for the aircraft in the approach phase towards the arrival airport on a second section, called an angular section, the angular deviation representing an angle formed at a touchdown point situated in proximity to a landing runway threshold between the target trajectory and a straight line joining the touchdown point to the estimated position of the aircraft;
• selecting between a linear scale and an angular scale for displaying the vertical or lateral component of the linear or angular deviation of the aircraft;
• converting the angular deviation into an equivalent linear deviation if the selected scale is the linear scale, or converting the linear deviation into an equivalent angular deviation if the selected scale is the angular scale;
• and
• displaying the vertical or lateral component of the equivalent linear deviation or the equivalent angular deviation on the selected linear or angular scale,
• wherein the method continuously monitors navigation performance, either on the angular or linear scale, independently of a switchover between a linear and an angular navigation.