Uncontrolled Descent and Collision with Terrain
United Airlines Flight 585
Boeing 737-200, N999UA
4 Miles South of Colorado Springs
Colorado Springs, Colorado
March 3, 1991
NTSB Number AAR-01/01
NTIS Number PB2001-910401
Synopsis: On March 3, 1991, a United Airlines Boeing 737, registration number N999UA, operating as flight 585, was on a scheduled passenger flight from Denver, Colorado, to Colorado Springs, Colorado. Visual meteorological conditions prevailed at the time, and the flight was on an instrument flight rules flight plan. Numerous witnesses reported that shortly after completing its turn onto the final approach course to runway 35 at Colorado Springs Municipal Airport, about 0944 mountain standard time, the airplane rolled steadily to the right and pitched nose down until it reached a nearly vertical attitude before hitting the ground in an area known as Widefield Park. The airplane was destroyed, and the 2 flight crewmembers, 3 flight attendants, and 20 passengers aboard were fatally injured.
The National Transportation Safety Board determines that the probable cause of the United Airlines flight 585 accident was a loss of control of the airplane resulting from the movement of the rudder surface to its blowdown limit. The rudder surface most likely deflected in a direction opposite to that commanded by the pilots as a result of a jam of the main rudder power control unit servo valve secondary slide to the servo valve housing offset from its neutral position and overtravel of the primary slide.
(Note: this report is a revision to AAR-92/06, and includes information developed after its adoption in December 1992.)