United Airlines Flight 585

United Airlines Flight 585

A United Airlines Boeing 737-200 Advanced similar to the one involved.
Accident summary
Date	March 3, 1991
Summary	Rudder hardover
Site	Security-Widefield, El Paso County near Colorado Springs, Colorado, United States
Passengers	20
Crew	5
Fatalities	25 (all)
Survivors	0
Aircraft type	Boeing 737-291
Operator	United Airlines
Registration	N999UA
Flight origin	Greater Peoria Regional Airport
Last stopover	Stapleton International Airport
Destination	Colorado Springs Municipal Airport

United Airlines Flight 585 was a scheduled passenger flight from the now-decommissioned Stapleton International Airport in Denver to Colorado Springs, Colorado.

On March 3, 1991, the Boeing 737-291 operating the flight, registered N999UA (previously N7356F with Frontier Airlines), carrying 20 passengers plus a flight crew of 5, crashed while on final approach to runway 35 at Colorado Springs Municipal Airport. There were no survivors.

Accident

The flight crew consisted of Captain Harold Green, 52, First Officer Patricia Eidson, 42, and Flight Attendants Lisa Church, Anita Lucero, and Monica Smiley. The captain, who had almost 10,000 flight hours, was regarded by colleagues as a conservative pilot who always followed standard operating procedures. The first officer had accumulated almost 4,000 flight hours and Captain Green considered her to be a very competent pilot.

Flight 585 left Peoria for Colorado Springs, with intermediate stops at Moline, Illinois and Denver, Colorado. 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, at 09:43. The aircraft then suddenly rolled to the right and pitched nose down. The crew tried to initiate a go-around by selecting 15-degree flaps and an increase in thrust. The altitude decreased rapidly and acceleration increased to over 4G until the aircraft crashed into nearby Widefield Park, less than four miles from the runway threshold, at a speed of 245 mph.

Investigations

The subsequent investigation by the NTSB lasted one year and nine months.

Although the flight data recorder outer protective case was damaged, the data tape inside was intact and all the data were recoverable. Five parameters were recorded: heading, altitude, airspeed, normal acceleration (G loads), and microphone keying. The data proved insufficient to establish why the plane suddenly went into the fatal dive. The NTSB considered the possibilities of a malfunction of the rudder power control unit servo (which might have caused the rudder to reverse) and the effect of powerful rotor winds from the nearby Rocky Mountains might have had, but there was not enough evidence to prove either hypothesis.

Thus, the first NTSB report (issued on 8 December 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."

Probable cause

The NTSB reopened the UAL 585 case after the crash of another 737, USAir Flight 427, which occurred three and a half years later. It was eventually determined that both crashes were the result of a sudden malfunction of the rudder power control unit. 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."

See also

• Boeing 737 rudder issues
• Eastwind Airlines Flight 517
• USAir Flight 427
• American Airlines Flight 1
• Northwest Airlines Flight 85

External links

• AirDisaster.com Special Report: United Airlines Flight 585
• Accident description at the Aviation Safety Network
• Boeing 737 Rudder Design Defect
• Airliners.net Pre-crash photos