Abstract: The theory of stability of differential equations is used to analyse the' effect of reversal slope of pitch moment to the stability of aircraft.It is believed that reversal slope range is one of the important factors which leads to sudden change of angle of attack and then the aircraft may proceed to post-stall flight when aircraft flies norimaneuverably at high angle of attack and low angle of sideslip. The width and the depth of the reversal slope range influence seriously the characteristics of this post-stall flight and its entry and recovery.

Key words: reversal slope of pitch moment curve, nonlinearity, the global stability, bifurcation analysis and catastropli}e bheory