Starting in 1991 , several accidents and incidents involving the Boeing 737 were the result of uncommanded movement of their rudders . On 3 March 1991 , United Airlines Flight 585 , a 737-200 , crashed in Colorado Springs , Colorado , killing 25 people . On 8 September 1994 , USAir Flight 427 , a 737-300 , crashed near Pittsburgh , Pennsylvania , killing 132 people . There were four more incidents where a 737 rudder power control unit ( PCU ) malfunction was suspected
USAir Flight 427
USAir Flight 427
SilkAir Flight 185