Accident
Last updated: 23 November 2014
Statuts:Enquête Officielle
Date:dimanche 3 mars 1991
Heure:09:44
Type/Sous-type:Silhouette image of generic B732 model; specific model in this crash may look slightly different
Boeing 737-291
Compagnie:United Airlines
Immatriculation: N999UA
Numéro de série: 22742/875
Année de Fabrication: 1982-05-11 (8 years 10 months)
Heures de vol:26050
Cycles:19734
Moteurs: 2 Pratt & Whitney JT8D-17
Equipage:victimes: 5 / à bord: 5
Passagers:victimes: 20 / à bord: 20
Total:victimes: 25 / à bord: 25
Dégats de l'appareil: Détruit
Conséquences: Written off (damaged beyond repair)
Lieu de l'accident:6,4 km (4 milles) S of Colorado Springs, CO (   Etats-Unis d'Amérique) show on map
Phase de vol: En approche (APR)
Nature:Transport de Passagers Nat.
Aéroport de départ:Denver-Stapleton International Airport, CO (DEN/KDEN), Etats-Unis d'Amérique
Aéroport de destination:Colorado Springs-Peterson Field, CO (COS/KCOS), Etats-Unis d'Amérique
Numéro de vol: 585
Détails:
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. (MST). 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.

Sources:
» Aviation Week & Space Technology 11.03.1991 (25-26)
» Flight International 14-21.12.1992 (34)
» NTSB Safety Recommendations A-92-57 and -58
» NTSB/AAR-92/06
» Scramble Vol.13, nr.04
» Scramble 165

Official accident investigation report
investigating agency: National Transport Safety Bureau (NTSB) - United States of America
report status: Final
report number: NTSB/AAR-01-01
report released:27-MAR-2001
duration of investigation:3677 days (10 years )
download report: Aircraft Accident Report: Uncontrolled Descent and Collision with Terrain, United Airlines Flight 585, Boeing 737-200, N999UA, 4 Miles South of Colorado Springs Municipal Airport Colorado Springs, Col (NTSB/AAR-01-01)
cover

Opérations de secours

NTSB issued 24 Safety Recommendations

Show all AD's and Safety Recommendations

Photos

photo of Boeing 737-291 N999UA
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Video/animation

Plan
Ce plan montre l'aéroport de départ ainsi que la supposé destination du vol. La ligne fixe reliant les deux aéroports n'est pas le plan de vol exact.
La distance entre Denver-Stapleton International Airport, CO et Colorado Springs-Peterson Field, CO est de 109 km (68 miles).

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