United Airlines Flight 585

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. The Boeing 737-200 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 on board died on impact.

The National Transportation Safety Board (NTSB) was initially unable to resolve the cause of the crash, but after similar accidents and incidents involving Boeing 737 aircraft, including the fatal crash of USAir Flight 427, the crash was determined to be caused by a defect in the design of the 737's rudder power control unit which caused the rudder to work in the opposite direction.

Accident

Flight 585 was a regularly scheduled 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 in Colorado Springs, CO, 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 40 knots and above." The flight crew added 20 knots 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 11000 ft. Colorado Springs Approach then cleared the flight for a visual approach to runway 35 (now 35L) 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 16 knots with gusts to 29 knots. At this moment, the aircraft was at 8000 ft. 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 15 knot loss at 500 ft, a 15 knot gain at 400 ft, and a 20 knot gain at 150 ft, 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, 5 mi 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 4 mi northeast of the accident when it occurred, and he had also reported slight, occasional, moderate chop at 7000 ft. The Cessna pilot had also noted indicated airspeed fluctuations between 65 knots and 105 knots with vertical speed indications of approximately 500 ft per minute.

At 09:41:23 (16:41:23 UTC), air traffic control directed Flight 585 to hold short of runway 30 after landing to allow 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 155 knots with 2 to 10 knot excursions.

About 20 seconds prior to the crash, the aircraft entered into a controlled 20-degree bank and turn for alignment with the runway. Around four seconds later, First Officer Eidson informed Captain Green that they were at 1000 ft.

Within the next four seconds, at 09:43:33 (16:43:33 UTC), the aircraft suddenly rolled to the right, heading rate increasing to about 5-degrees per second as a result, nearly twice that of a standard rate turn, and pitched nose down. First Officer Eidson stated "Oh God, [flip]!", and in the same moment Captain Green called for 15-degrees of flaps while increasing thrust, in an attempt to initiate a go-around. The altitude decreased rapidly and acceleration increased to over 4G until, at 09:43:41 (16:43:41 UTC), the aircraft crashed at an 80-degree nose-down angle, yawed 4-degrees to the right, into Widefield Park, less than 4 mi from the runway threshold, at a speed of 245 mph. The aircraft was destroyed on impact and by the post-crash fire. According to the accident report, the crash carved a crater 39 x 24 ft and 15 ft deep. Segments of the 737 were buried deep within this crater, requiring excavation. Everyone on board was killed instantly. The aircraft narrowly missed a row of apartments; a girl standing in the doorway of one of the apartments was knocked backwards by the force of the explosion, hitting her head, but was released from a local hospital with no further problems after treatment.