Aircraft integrity

For the concept of integrity applied to aircraft navigation via satellite navigation, imagine the aircraft in question with horizontal and vertical circles around it, taking in all the permissible places it might be, known as its ‘protection levels’. Around these in turn are wider circles representing its ‘alert level’ – so called because when the combined uncertainty level reaches this threshold then an alarm is raised to the user. The aim is to provide full confidence in the navigation system, including the ability to detect when the system should not be used for navigation.