A method includes repeatedly determining a distance of an aircraft from a landing location. The method also includes, during a first stage in which the aircraft is at least a threshold distance from the landing location, performing iono-free processing during navigation of the aircraft. The method further includes, during a second stage in which the aircraft is less than the threshold distance from the landing location and a velocity of the aircraft is greater than a velocity threshold, performing divergence-free processing during navigation of the aircraft to address possible ionospheric threats. In addition, the method includes, during a third stage in which the aircraft is less than the threshold distance from the landing location and the velocity of the aircraft is less than the velocity threshold, calculating one or more floor values for a Differential Ionospheric Correction (DIC) sigma, and determining a navigation solution to protect against nominal ionospheric conditions.