TERRAIN FOLLOWING APPARATUS FOR A VEHICLE

A Terrain Following Apparatus for a vehicle such as an aircraft includes means (1) for effecting autonomous following of terrain by the vehicle, a control device (2), operable by a person operating the vehicle, to engage and disengage the means (1), a Terrain Referenced Navigation system (3) operable to provide navigation data for the vehicle, and validation means (4) for validating the integrity of the navigation data to provide when the integrity of the navigation data is validated for engagement of the autonomous Terrain Following means (1) by the device (2) and when the integrity of the navigation data is invalidated, for preventing operation of the means (1) when the control device (2) is operated.