INS/Baro vertical channel performance using improved pressure altitude as a reference

An altitude reference is usually required to damp the error growth in the inherently unstable vertical channel of an Inertial Navigation System (INS) for long flights. The solution for INS vertical channel in GPS-denied environments commonly uses a Baro altitude for reference in an INS/Baro system. The Baro altitude is usually obtained by computing the pressure altitude based on a standard atmospheric model for the standard day via the aircraft Central Air data computer (CADC). However, due to significant errors in pressure altitude, the altitude and vertical velocity errors exhibited by the pressure altitude stabilized vertical channel can be unacceptably large and this can adversely impact applications requiring high accuracy. A more accurate altitude and velocity of the INS vertical channel can be achieved by using a pressure altitude algorithm with improved modeling. This paper describes the performance results (altitude and velocity errors) for a vertical channel using pressure altitude with improved error modeling that demonstrates excellent results. The INS errors and pressure altitude errors are estimated by a Kalman filter. Flight test data obtained from flights of an aircraft with high dynamic maneuvers are post processed using the new vertical channel. The results of the new vertical channel exhibit excellent performance for altitude and vertical velocity errors. The flight tests are described and the performance results with the new vertical channel mechanization are presented in the paper.