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NTSB Report
October 24, 1991 · Boeing 747-122 · N4719U
Denver, CO
Overview
Report Status
Probable Cause
Event Type
Incident
Date
October 24, 1991
Injury Outcomes
No injuries (280 uninjured)
Location
Denver, CO
Aircraft
Boeing 747-122
Tail Number
N4719U
Operator
United Airlines
Injuries
None
NTSB Number
DEN92IA005
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.
NTSB Probable Cause
A MALFUNCTION IN THE STABILIZER TRIM CONTROL MODULE.
Full Narrative
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.
Flight
Event TypeIncident
Event Time14:00 MDT
Nearest Airport0nm N
Runway0
Flight Plan FiledIFR
Aircraft FireNo
Aircraft ExplosionNo
Aircraft
AircraftBoeing 747-122
Tail NumberN4719U
Aircraft CategoryAir
OperatorUnited Airlines
Operating RulePart 121
Engines4
Engine TypeTurbofan
Engine DetailsP&W · JT9D · Turbofan · 45800
Seats495
People & Injuries
Injury SummaryNo injuries (280 uninjured)
Fatal0
Serious0
Minor0
Uninjured280
Total280
Crew 1Unknown
Conditions
ConditionsVMC
LightDaylight
WindCalm
CeilingNone
Temperature / Dew Point0 C / 0 C
Altimeter0
Weather SourcePILO