# NTSB DEN92IA005: Boeing 747-122, N4719U, Denver, CO, October 24, 1991

- Type: NTSB incident investigation
- Classification: Incident · No injuries · Incident investigation · Final report
- Date: October 24, 1991, 14:00 local (20:00 UTC)
- Place: Denver, CO
- Coordinates: 39.789226, -104.960266 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=39.7892&lon=-104.9603&mi=10
- Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 280 uninjured
- Status: Completed, report May 5, 1993
- Report: Approved by Office Director
- NTSB case key (mKey): 18164
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=DEN92IA005
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/18164/pdf
- Page: https://openairdocs.org/ntsb/DEN92IA005

## Probable cause

A MALFUNCTION IN THE STABILIZER TRIM CONTROL MODULE.

## Analysis

DURING LEVEL OFF AT FLIGHT LEVEL 290, WHILE ON A SCHEDULED INTERNATIONAL PASSENGER FLIGHT FROM SAN FRANCISCO, CALIFORNIA, TO LONDON, ENGLAND, ELEVATOR PITCH CONTROL BECAME ERRATIC AND OSCILLATIONS OF UP TO 1,000 FEET EITHER SIDE OF THE BASE ALTITUDE OCCURRED.  THE AUTO PILOT WAS DISCONNECTED, COMMUNICATIONS WITH MAINTENANCE CONTROL WAS HELD, AND THE FLIGHT PROCEEDED TO THE NEAREST AIRPORT WITH RUNWAYS EXCEEDING 10,000 FEET IN LENGTH.  AN UNEVENTFUL PRECAUTIONARY LANDING WAS CONDUCTED IN DENVER, COLORADO.  STABILIZER TRIM COMPONENTS WERE EXAMINED REVEALING DISCREPENCIES IN THE TRIM MODULE AND ELEVATOR FEEL COMPUTER, DUE TO NORMAL WEAR.

## Sequence of events

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

- Altitude deviation,uncontrolled, cruise - normal
  - flt control syst,elevator control - erratic (cause)
- Forced landing, descent - emergency
  - precautionary landing - performed, pilot in command

## Aircraft

- Registration: [N4719U](https://openairdocs.org/deregistered/N4719U-1998-08-06), registration cancelled 1998-08-06, S/N 19880 (OpenAirDocs)
- Reported make and model: BOEING 747-122
- Registry model: [Boeing 747-122](https://openairdocs.org/model/boeing-747-122) (registry code 1384872) (OpenAirDocs)
- Category: Airplane
- Serial number: 8019
- Engines: P&W JT9D 45800 lbs thrust turbo fan
- Damage: No damage
- Flight: Part 121
- Operator: United Airlines
- Registered owner: United Airlines
- Airworthiness certificate: Standard, Transport
- Last inspection: Continuous airworthiness, January 2, 2000
- Departed: SFO, SAN FRANCISCO, CA
- Destination: LHR, LONDON
- Flight plan: IFR

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; airline transport; airplane ratings: multi-engine land; instrument ratings: airplane; medical: unknown, unknown; seat: left; flight hours: 25,000 total

## Weather

- Conditions: Visual (VMC), Day

## FAA reports on this event (1)

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

- [Incident 19911024057319I](https://openairdocs.org/incident/19911024057319I), Oct 24, 1991: Boeing 747122, Denver, CO. Had pitch control malfunction en route. Diverted to Denver. Found cadc and elevator field computers inoperative.

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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