United Airlines Flight 585
Encyclopedia
United Airlines Flight 585 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 3 March 1991, the Boeing 737-200
, registered , carrying 20 passengers plus a flight crew of 5 (Captain Harold Green, 52, First Officer Patricia Eidson, 42, 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 4g
. The 737 crashed into nearby Widefield Park
, less than four miles from the runway threshold.
lasted one year and 9 months.
Although the flight data recorder
(FDR) outer protective case was damaged, the foil tape inside was intact and all the data was extractable. The FDR only recorded five parameters: 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 (PCU) servo
(which might have caused the rudder to reverse) and the effect that powerful rotor winds coming off of 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."
, 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."
show Mayday
(known as Air Emergency in the US, Mayday in Ireland and Air Crash Investigation in the UK and the rest of world). The episode is entitled "Hidden Danger".
Airline
An airline provides air transport services for traveling passengers and freight. Airlines lease or own their aircraft with which to supply these services and may form partnerships or alliances with other airlines for mutual benefit...
flight from the now-decommissioned Stapleton International Airport
Stapleton International Airport
Stapleton International Airport was Denver, Colorado's primary airport from 1929 to 1995. At different times it served as a hub for TWA, People Express, Frontier Airlines and Western Airlines as well as a hub for Continental Airlines and United Airlines at the time of its closure.In 1995 Stapleton...
in Denver
Denver, Colorado
The City and County of Denver is the capital and the most populous city of the U.S. state of Colorado. Denver is a consolidated city-county, located in the South Platte River Valley on the western edge of the High Plains just east of the Front Range of the Rocky Mountains...
to Colorado Springs Municipal Airport in Colorado Springs, Colorado
Colorado Springs, Colorado
Colorado Springs is a Home Rule Municipality that is the county seat and most populous city of El Paso County, Colorado, United States. Colorado Springs is located in South-Central Colorado, in the southern portion of the state. It is situated on Fountain Creek and is located south of the Colorado...
.
On 3 March 1991, the Boeing 737-200
Boeing 737
The Boeing 737 is a short- to medium-range, twin-engine narrow-body jet airliner. Originally developed as a shorter, lower-cost twin-engine airliner derived from Boeing's 707 and 727, the 737 has developed into a family of nine passenger models with a capacity of 85 to 215 passengers...
, registered , carrying 20 passengers plus a flight crew of 5 (Captain Harold Green, 52, First Officer Patricia Eidson, 42, and three flight attendants) crashed while on final approach to runway
Runway
According to ICAO a runway is a "defined rectangular area on a land aerodrome prepared for the landing and take-off of aircraft." Runways may be a man-made surface or a natural surface .- Orientation and dimensions :Runways are named by a number between 01 and 36, which is generally one tenth...
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
Thrust
Thrust is a reaction force described quantitatively by Newton's second and third laws. When a system expels or accelerates mass in one direction the accelerated mass will cause a force of equal magnitude but opposite direction on that system....
increase and 15-degree flap
Flap (aircraft)
Flaps are normally hinged surfaces mounted on the trailing edges of the wings of a fixed-wing aircraft to reduce the speed an aircraft can be safely flown at and to increase the angle of descent for landing without increasing air speed. They shorten takeoff and landing distances as well as...
s were unsuccessful. As the altitude decreased, acceleration increased to 4g
G-force
The g-force associated with an object is its acceleration relative to free-fall. This acceleration experienced by an object is due to the vector sum of non-gravitational forces acting on an object free to move. The accelerations that are not produced by gravity are termed proper accelerations, and...
. The 737 crashed into nearby Widefield Park
Security-Widefield, Colorado
Security-Widefield is a census-designated place in El Paso County, Colorado, United States. The population was 29,845 at the 2000 census.-Geography:Security-Widefield is located at ....
, less than four miles from the runway threshold.
Investigations
The subsequent investigation by the NTSBNational Transportation Safety Board
The National Transportation Safety Board is an independent U.S. government investigative agency responsible for civil transportation accident investigation. In this role, the NTSB investigates and reports on aviation accidents and incidents, certain types of highway crashes, ship and marine...
lasted one year and 9 months.
Although the flight data recorder
Flight data recorder
A flight data recorder is an electronic device employed to record any instructions sent to any electronic systems on an aircraft. It is a device used to record specific aircraft performance parameters...
(FDR) outer protective case was damaged, the foil tape inside was intact and all the data was extractable. The FDR only recorded five parameters: 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 (PCU) servo
Servomechanism
thumb|right|200px|Industrial servomotorThe grey/green cylinder is the [[Brush |brush-type]] [[DC motor]]. The black section at the bottom contains the [[Epicyclic gearing|planetary]] [[Reduction drive|reduction gear]], and the black object on top of the motor is the optical [[rotary encoder]] for...
(which might have caused the rudder to reverse) and the effect that powerful rotor winds coming off of the nearby Rocky Mountains
Rocky Mountains
The Rocky Mountains are a major mountain range in western North America. The Rocky Mountains stretch more than from the northernmost part of British Columbia, in western Canada, to New Mexico, in the southwestern United States...
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 B-737, USAir Flight 427USAir Flight 427
US Air Flight 427 was a scheduled flight from Chicago's O'Hare International Airport to Pittsburgh, with a final destination of West Palm Beach, Florida...
, 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."
Dramatization
The story of the disaster was featured on the sixth season of Canadian National Geographic ChannelNational Geographic Channel
National Geographic Channel, also commercially abbreviated and trademarked as Nat Geo, is a subscription television channel that airs non-fiction television programs produced by the National Geographic Society. Like History and the Discovery Channel, the channel features documentaries with factual...
show Mayday
Mayday (TV series)
Mayday, also known as Air Crash Investigation in the United Kingdom, Australia and Asia and Air Emergency and Air Disasters in the United States, is a Canadian documentary television programme produced by Cineflix investigating air crashes, near-crashes and other disasters...
(known as Air Emergency in the US, Mayday in Ireland and Air Crash Investigation in the UK and the rest of world). The episode is entitled "Hidden Danger".
See also
- Accidents and incidents in aviation
- Boeing 737 rudder issuesBoeing 737 rudder issuesStarting in 1991, a number of accidents and incidents involving the Boeing 737 were the result of the airplanes' unexpected movement of their rudders. The rudder is controlled by the Power Control Unit . Inside the PCU is a dual servo valve which helps direct hydraulic fluid in order to move the...
- USAir Flight 427USAir Flight 427US Air Flight 427 was a scheduled flight from Chicago's O'Hare International Airport to Pittsburgh, with a final destination of West Palm Beach, Florida...
- Eastwind Airlines Flight 517Eastwind Airlines Flight 517Eastwind Airlines Flight 517 was a scheduled flight from Trenton-Mercer Airport in Trenton, New Jersey to Richmond International Airport in Richmond, Virginia. The crew lost rudder control but successfully landed on June 9, 1996. No casualties occurred and one flight attendant suffered only minor...
- Loss of control