Event Details

Title:Uncontrolled Descent and Collision With Terrain, United Airlines Flight 585, Boeing 737-200, N999UA, 4 Miles South of Colorado Springs Municipal Airport, Colorado, Springs, Colorado, March 3, 1991
Micro summary:This Boeing 737 encountered an in-flight upset and crashed.
Event Time:1991-03-03 at 0944 MST
File Name:1991-03-03-2-US.pdf
Publishing Agency:National Transportation Safety Board (NTSB)
Publishing Country:USA
Report number:NTSB/AAR-01/01
Site of event:3.47 nm south of COS RWY 35
Latitude/Longitude:N3844'09.4 W10442'42.4"
Departure:Denver Stapleton International Airport, Denver, Colorado, USA
Destination:Colorado Springs Airport, Colorado Springs, Colorado, USA
Airplane Type(s):Boeing 737-291 (ADV)
Flight Phase:Descent
Operator(s):United Airlines
Type of flight:Revenue
Serious Injuries:0
Other Injuries:0
Executive Summary:Abstract: This amended report explains the accident involving United Airlines flight 585, a Boeing 737-200, which entered an uncontrolled descent and impacted terrain 4 miles south of Colorado Springs Municipal Airport, Colorado Springs, Colorado, on March 3, 1991. Safety issues discussed in the report are the potential meterological hazards to airplanes in the area of Colorado Springs; 737 rudder malfunctions, including rudder reversals; and the design of the main rudder power control unit servo valve.

Executive Summary 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.
Learning Keywords:Operations - Uncontrolled Flight into Terrain
Operations - Upset in-flight (extreme attitudes, stall, spin)
Systems - Flight Control System
Other - Boeing 737 In-flight upsets
Other - Certification
Consequence - Hull Loss
Close match:Final report of the accident investigation, Flash Airlines Fight 604, Boeing 737-300 SU-ZCF, Red Sea off Sharm El-Sheikh, Egypt, January 3, 2004
Descent from cruise and crash into river, Aircraft Accident Report, Silkair Flight MI 185, Boeing B737-300, 9V-TRF, Musi River, Palembang, Indonesia, 19 December 1997
In-Flight Fire And Impact with Terrain, Valujet Airlines Flight 592, DC-9-32, N904VJ, Everglades, Near Miami, Florida, May 11, 1996
In-flight upset, United Airlines Flight 585, Boeing 737-291, N999UA, Uncontrolled Collision with Terrain for Undetermined Reasons, 4 Miles South Of Colorado Springs Municipal Airport, Colorado Springs, Colorado, March 3, 1991


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