United Airlines Flight 585 was a scheduled passenger flight on March 3, 1991, from Denver to Colorado Springs, Colorado, carrying 20 passengers and 5 crew members on board. The plane experienced a rudder hardover while on final approach to runway 35 at Colorado Springs Municipal Airport, causing the plane to roll over and enter an uncontrolled dive. All 25 people on board were killed.
The NTSB was initially unable to resolve the cause of the crash, but after similar accidents and incidents involving Boeing 737 aircraft, the crash was determined to be caused by a defect in the design of the 737's rudder power control unit.
Aircraft and flight crew
Flight 585 was operated by a Boeing 737-291, registered . The 737 was originally manufactured for the original incarnation of Frontier Airlines in 1982 and was acquired by United Airlines in 1986 when the former went out of business (a new airline company with the same name formed eight years later). On the date of the accident, the aircraft had accumulated approximately 26,000 flight hours.
The captain of the flight was Harold Green, age 52. He had over 10,000 hours as a United Airlines pilot (including 1,732 hours on the Boeing 737), was regarded by colleagues as a conservative pilot who always followed standard operating procedures. The first officer was Patricia Eidson, age 42. She had accumulated over 4,000 flight hours (including 1,077 hours on the Boeing 737), and she was considered by the captain to be a very competent pilot.
On February 25, 1991, the aircraft was flying at when the rudder abruptly deflected 10 degrees to the right. The crew on board reduced power and the aircraft returned to normal flight. A similar event occurred two days later. Four days later, the aircraft crashed.
Accident
Flight 585 was a regularly scheduled United Airlines Flight, originating at General Wayne A. Downing Peoria International Airport in Peoria, Illinois to Colorado Springs, Colorado, making intermediate stops at Quad City International Airport in Moline, Illinois, with an intended final stop at the now-decommissioned Stapleton International Airport in Denver, Colorado, at 09:46 Mountain Standard Time (16:46 UTC). On March 3, 1991, the flight operated from Peoria to Denver without incident.
At 09:23 (16:23 UTC), Flight 585 departed Denver with 20 passengers and 5 crew members on board. At 09:30:37 (16:30:37 UTC), the aircraft received Automatic terminal information service "Lima", that was about 40 minutes old, stating "Wind three one zero at one three gust three five; low level wind shear advisories are in effect, local aviation wind warning in effect calling for winds out of the northwest gust to and above." The flight crew added to their target landing airspeed based on this information.
At 09:32:35, First Officer Eidson reported to Colorado Springs Approach Control that their altitude was . Colorado Springs Approach then cleared the flight for a visual approach to runway 35 and instructed the flight to contact Colorado Springs Tower.
At 09:37:59 (16:37:59 UTC) Colorado Springs Tower cleared Flight 585 to land on runway 35, notifying the flight that wind was 320 degrees at with gusts to . At this moment, the aircraft was at . First Officer Eidson inquired about reports from other aircraft about airspeed changes, and at 09:38:29 (16:38:29 UTC) the tower replied that another 737 had reported a loss at , a gain at , and a gain at , at approximately 09:20 (16:20 UTC), 17 minutes prior. Eidson replied, "Sounds adventurous... United five eighty-five, thank you."
At 09:40:07 (16:40:07 UTC), Flight 585 was informed of traffic, a Cessna at their eleven o'clock, northwest bound, landing at runway 30. The crew was unable to locate the traffic, but 37 seconds after it was reported, the tower informed the flight that the traffic was now behind them. This Cessna was located about northeast of the accident when it occurred, and he had also reported slight, occasional, moderate chop at . The Cessna pilot had also noted indicated airspeed fluctuations between and with vertical speed indications of approximately per minute.
At 09:41:23 (16:41:23 UTC), air traffic control directed Flight 585 to hold short of runway 30 for departing traffic. Eidson replied "We'll hold short of three-zero, United five eighty five." This was the last transmission received from the flight.
In the final minute of the flight, normal acceleration varied between 0.6-1.3g, with an airspeed of with 2 to 10 knot excursions.