Abstract: Methods and apparatus for determining altitude, specifically altitude in an aircraft, and an estimated error of the altitude. The altitude determination preferably uses a first altitude based on hydrostatic calculations, including local pressure and temperature, as well as a second altitude which is preferably a GPS altitude. A radio altimetry can also be used instead of or to complement the GPS altitude. Other sources of altitude determination can be used in the equation for the calculation of the final altitude. Each of the sources of altitude determination is provided with a complementary estimated error. In the final determination of the probable altitude, each source of altitude information is preferably accorded a weighting according to the estimated error of the altitude source. For global positioning altitude, the final combination of the altitude sources uses a complementary filter which takes into account the selective availability of the GPS altitude.

Abstract: A terrain awareness system and method which provides increased warning times to the pilot of an aircraft of a hazardous flight condition while minimizing nuisance warnings. An important aspect of the invention is that the terrain background information as well as the terrain advisory and warning indications may be displayed on a navigational or weather display, normally existing within an aircraft, which reduces the cost of the system and obviates the need for extensive modifications to existing displays, such as a navigational and weather radar type display.