The ground based radar tracking guidance computer calculates the aircraft position and transmits it to the aircraft by the up-link telemeter system. The telemeter receiver onboard the aircraft outputs this radar data to the Telemeter/HUD(TEL/HUD) inter-face. The TEL/HUD interface smoothes the radar position data by using the complementary filter shown in Fig.15, using the inertial velocities from the IRU This also removes the drifts from the inertial velocities. When a radar guidance mode is engaged, the HUD gets an initial value of the aircraft positions from the complementary filter.
Fig.15 Complementary Filter Block Diagram
Table 1 Complementary Filter Input-Output Table
The TEL/HUD interface integrates the inertial velocities from the initial position to get continuous position data for the perspective runway. When the error in the integrated position as compared with the radar data of the complementary filter output becomes more than 10 meters, HUD calculations get new correct initial values. In addition to trajectory and aircraft position information; ground speed, track angle, drift angle, arid wind data are calculated using these data in the TEL/HUD interface. These new data with a selected approach path angle and the runway heading are output to the HUD to display the perspective runway conformal with the real runway. As the flight path symbol now indicates correctly the direction of
