Date:	Sunday 3 March 1991
Time:	09:44
Type:	Boeing 737-291
Owner/operator:	United Airlines
Registration:	N999UA
MSN:	22742/875
Year of manufacture:	1982
Total airframe hrs:	26050 hours
Cycles:	19734 flights
Engine model:	Pratt & Whitney JT8D-17
Fatalities:	Fatalities: 25 / Occupants: 25
Aircraft damage:	Destroyed, written off
Category:	Accident
Location:	6,4 km S of Colorado Springs, CO -   United States of America
Phase:	Approach
Nature:	Passenger - Scheduled
Departure airport:	Denver-Stapleton International Airport, CO (DEN/KDEN)
Destination airport:	Colorado Springs-Peterson Field, CO (COS/KCOS)
Investigating agency:	NTSB
Confidence Rating:	Accident investigation report completed and information captured

Narrative:
United Airlines flight 585 left Peoria for Colorado Springs, with intermediate stops at Moline, IL and Denver, CO. The aircraft took off from Denver at 09:23 for the last segment of the flight, estimating Colorado Springs at 09:42. The aircraft was cleared for a visual approach to runway 35. The aircraft then suddenly rolled to the right and started to pitch nose down. The crew tried to initiate a go-around by selecting 15-deg. flaps and an increase in thrust. The altitude decreased rapidly, acceleration increased to over 4G until the aircraft struck the ground of Widefield Park almost vertically.
After a 21-month investigation, the NTSB issued a report on the crash in December 1992. In that report, the NTSB said it 'could not identify conclusive evidence to explain the loss of' the aircraft, but indicated that the two most likely explanations were a malfunction of the airplane’s directional control system or an encounter with an unusually severe atmospheric disturbance.

Investigation into a September 1994 crash of a USAir Boeing 737-300 and an loss of control incident on June 9, 1996 (Eastwind Airlines Boeing 737-200), cited a malfunction in the plane’s rudder system as the most likely cause of all three events.

PROBABLE CAUSE: "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."

Aviation Week & Space Technology 11.03.1991 (25-26)
Flight International 14-21 December 1992 (34)
NTSB Safety Recommendations A-92-57 and -58
NTSB/AAR-92/06
Scramble Vol.13, nr.04
Scramble 165

photo (c) Werner Fischdick; Denver-Stapleton International Airport, CO (DEN); 31 July 1988

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