Patent ID: 7479923

Claim:
A method of analysing position data relating to an airborne platform, the method comprising: providing an indication of reliability of position data relating to the airborne platform responsive to a comparison between one or more predetermined thresholds and the difference between a measure of rate of change of pressure altitude and a measure of rate of change of geometric altitude in which the comparison is made based on the relationship: T T * ⁢ ω ≈ w + f g ⁢ s ⁢ ⁢ σ in which: T is the air temperature, T* is the air temperature in the standard atmosphere, ω is the rate of change of pressure altitude, w is the rate of change of geometric altitude ƒ is the Coriolis parameter g is gravitational acceleration s is the air speed of the aircraft, and σ is the crosswind experienced by the aircraft.