Aircraft height monitoring is one of the requirements for reducing the vertical separation minimum above flight level 290 from 2,000 ft to 1,000 ft. As a subsystem of the height monitoring system, a simple Secondary Surveillance Radar(SSR) was developed. Flight experiments were carried out for evaluating the performance of the SSR. Obtained SSR data were analyzed by comparing with the GPS positioning data collected for the experimental flights. The results are as follows. 1) The average of the range error Δr is -37 m and standard deviation of Δr is 29 m. 2) The frequency of extremely large absolute azimuth errors (±180°) is approximately 10%. 3) The data shown in 2) can be reduced by simple tracking procedures.
