# NTSB DCA91MA023: Boeing 737-291, N999UA, Colorado Spgs, CO, March 3, 1991

- Type: NTSB accident investigation
- Classification: Accident · Fatal · Class 1 · Major · Final report
- Date: March 3, 1991, 09:44 local (16:44 UTC)
- Place: Colorado Spgs, CO
- Location: 38.8339° N, 104.8214° W: Placed by OpenAirDocs: center of Colorado Springs, CO, within about 8 miles (OpenAirDocs)
- Nearby events: https://openairdocs.org/map.md?lat=38.8339&lon=-104.8214&mi=10
- Phase of flight: [Approach](https://openairdocs.org/ntsb-phases/500) (OpenAirDocs' grouping)
- Highest injury: Fatal
- Injuries: 25 fatal
- Status: Completed, report August 5, 1993
- Report: Board-adopted at Board Meeting
- Investigation class: Class 1
- NTSB office: Major Investigations Division
- Safety recommendations: Yes
- NTSB case key (mKey): 15948
- NTSB case page: https://www.ntsb.gov/investigations/Pages/DCA91MA023.aspx
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/15948/pdf
- Board report AAR0101 (PDF): https://www.ntsb.gov/investigations/AccidentReports/Reports/AAR0101.pdf
- Page: https://openairdocs.org/ntsb/DCA91MA023

## Probable cause

A loss of control of the airplane resulting from the movement of the rudder surface to its blowdown limit. 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.

## Sequence of events

In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf).

- Airframe/component/system failure/malfunction, approach
  - flight control,rudder surface - uncommanded (cause)
  - flight control,rudder - jammed (cause)
- Loss of control - in flight, descent - uncontrolled
  - aircraft control - not possible
- In flight collision with terrain/water, descent - uncontrolled
  - terrain condition - ground

## Analysis

Executive Summary

On March 3, 1991, a United Airlines (UAL) Boeing 737, registration number N999UA, operating as flight 585, was on a scheduled passenger flight from Denver, Colorado, to Colorado Springs, Colorado. Visual meteorological conditions (VMC) prevailed at the time, and the flight was on an instrument flight rules (IFR) flight plan. Numerous witnesses reported that shortly after completing its turn onto the final approach course to runway 35 at Colorado Springs Municipal Airport (COS), about 0944 Mountain Standard Time, the airplane rolled steadily to the right and pitched nose down until it reached a nearly vertical attitude before hitting the ground in an area known as Widefield Park. The airplane was destroyed, and the 2 flight crewmembers, 3 flight attendants, and 20 passengers aboard were fatally injured.

## Aircraft

- Registration: [N999UA](https://openairdocs.org/deregistered/N999UA-1992-02-05), registration cancelled 1992-02-05, S/N 22742 (OpenAirDocs)
- Reported make and model: BOEING 737-291
- Registry model: [Boeing 737-291](https://openairdocs.org/model/boeing-737-291) (registry code 138448W) (OpenAirDocs)
- Category: Airplane
- Serial number: 22742
- Airframe hours: 26050
- Engines: P&W JT8D-17 15000 lbs thrust turbo jet
- Damage: Destroyed
- Fire: On-Ground
- Flight: Part 121
- Operator: United Airlines
- Registered owner: United Airlines
- Airworthiness certificate: Standard, Transport
- Last inspection: Continuous airworthiness, May 27, 1990, 2,046 hours before
- Departed: DEN, DENVER, CO
- Flight plan: IFR

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 52; commercial, flight engineer, airline transport; airplane ratings: multi-engine land, single-engine land; instrument ratings: airplane; medical: class 1, valid medical--w/ waivers/lim; seat: left; toxicology performed; flight hours: 9,902 total, 1,732 in this make and model

## Weather

- Conditions: Visual (VMC), Day
- Wind: 330° at 23 knots, gusting 33
- Visibility: 99 statute miles
- Lowest ceiling: none
- Temperature: 48 °F, dew point 9 °F
- Altimeter: 30.00 inHg
- Observed at: COS, 3 nm away

## FAA reports on this event (1)

The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs).

- [Accident 19910303003669A](https://openairdocs.org/incident/19910303003669A), Mar 3, 1991: Boeing 737291, Colorado Spring, CO, Destroyed, 25 fatal. Rolled vertical on final and dived into ground. Windshear sigmets and rotor clouds in area. Rudder and wind suspects

From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model.

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