Abstract: This paper discussed a kind of Kalman filter used in the pilotless helicopter hov er ing flight with small radius and stable v elocity . The authors put forward st ate equations of this flight mo de, the auto-judging method at entrance or ex it of the hovering flight mode, and the auto-processing method on outlier data rejection. T his paper givest he error analysis o n data process and false alarm probability of flight mode judgment using t he filter. This filter canbe used in nav igation, antenna tracking, and telemetry data processing systems to improve the locating accur acy andto r ealize the flig ht mode auto judgment.

Key words: Kalman filter, circle flight, mode judgment, outli er rejection