Methods, apparatus and computer program products for determining the vertical speed of an aircraft

A method, an apparatus and a computer program product are provided for accurately determining the vertical speed of an aircraft in a manner independent of signals provided by an air data computer, an inertial reference system and an inertial navigation system. Initially, a first vertical velocity of the aircraft is determined based upon a pressure altitude value associated with the aircraft. A second vertical velocity of the aircraft is also obtained from a GPS receiver carried by the aircraft. The first and second vertical velocities are then combined to determine the vertical speed of the aircraft. In this regard, the first and second vertical velocities are combined by complimentarily filtering the first and second vertical velocities. More particularly, the first vertical velocity is typically low pass filtered to remove high frequency noise that is attributable to the relatively low resolution of the first vertical velocity value. Additionally, the second vertical velocity is typically high pass filtered to reduce errors due to long-term drift. Thus, the vertical speed of the aircraft is determined according to the present invention so as to have the best attributes of both the first and second vertical velocity values while eliminating the most common types of errors included within the first and second vertical velocity values.