was a scheduled domestic passenger
Airline flight from the now-decommissioned
Stapleton International Airport in
Denver to
Colorado Springs Municipal Airport in
Colorado Springs, Colorado .
On
March 3 ,
1991 , the
Boeing 737-200 , registered , carrying 20 passengers plus a flight crew of 5 (Captain Harold Green, First Officer Patricia Eidson and three flight attendants) crashed while on final approach to
Runway 35, at the Colorado Springs airport. There were no survivors.
Flight 585 suddenly rolled to the right and began to pitch downward, nose first. Attempts to initiate a go-around using a
Thrust increase and 15-degree
Flap s were unsuccessful. As the altitude decreased, acceleration increased to 4
''g'' . The 737 crashed into nearby
Widefield Park , exploding on impact, less than 4 miles from the runway threshold.
Patricia Eidson was the second female pilot to die in an accident involving a United States commercial airliner. The first female pilot fatality, was that of First Officer Zilda A. Spadaro-Wolan, in the Henson Airlines flight 1517 crash of September 23, 1985 near Grottoes, Virginia.
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The subsequent investigation by the
NTSB lasted one year and 9 months.
The
Flight Data Recorder only recorded five parameters: heading; altitude; airspeed; normal acceleration (G loads); and
microphone keying. Although the FDR outer protective case was damaged, the foil tape was intact and all the data was extractable. But, that proved insufficient to establish why the plane suddenly went into the fatal dive. The NTSB did consider the possibilities of a malfunction of the rudder PCU servo (which might have caused the rudder to reverse), and the effect that powerful rotor winds coming off of the mountains, might have had, but there simply wasn't enough evidence to prove either scenario.
Thus the first NTSB report (issued on December 8, 1992), did not conclude with the usual "probable cause." Instead, it said "The National Transportation Safety Board, after an exhaustive investigation effort, could not identify conclusive evidence to explain the loss of United Airlines flight 585."
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However, after the crash of another B-737,
USAir Flight 427 , the NTSB was forced to re-open the UAL 585 case. It was finally determined that both crashes were the result of a sudden malfunction of the
Rudder power control unit (PCU). The pilots lost control of the airplane because "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."
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