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Aviation safety reports, made easier to study

NTSB Reports is an independent research and search tool for public aviation accident and incident records. It brings NTSB aviation reports, structured fields, docket files, extracted figures, photos, videos, and update history into one searchable interface.

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NTSB Report

February 14, 1993 · Boeing 757-222 · N508UA

Grand Junction, CO

Overview

Report Status
Probable Cause
Event Type
Incident
Date
February 14, 1993
Injury Outcomes
No injuries (47 uninjured)
Location
Grand Junction, CO
Aircraft
Boeing 757-222
Tail Number
N508UA
Operator
United Airlines
Injuries
None
NTSB Number
DEN93IA027

WHILE CRUISING AT FL390, THE AUTOTHROTTLES AND AUTOPILOT DISENGAGED, THE CAPTAIN'S INSTRUMENTS FAILED, AND THE COCKPIT LIGHTING CYCLED ON AND OFF. THE LEFT GENERATOR LIGHT ILLUMINATED, THE EICAS FAILED, A CYCLIC BANGING WAS HEARD, AND AN ACRID ODOR WAS NOTICEABLE. THE LEFT AC BUS AND TRANSFER BUS WERE DEENERGIZED AND THE CAPTAIN ELECTED TO DIVERT TO THE NEAREST SUITABLE AIRPORT. POST INCIDENT INVESTIGATION DISCLOSED A SHORTED DIODE IS THE LEFT GCU (GENERATOR CONTROL UNIT), A DEFECTIVE IDG (INTEGRATED DRIVE GENERATOR), A SHORT IN THE INPUT POWER FILTER IN THE EICAS (ENGINE INDICATOR AND CREW ALERT SYSTEM), AND A DEFECTIVE BTB (BUS TIE BAR).

NTSB Probable Cause

FAILURE OF THE LEFT GENERATOR CONTROL UNIT (GCU), INTEGRATED DRIVE GENERATOR (IDG), RIGHT (SIDE) ENGINE INDICATOR AND CREW ALERT SYSTEM (EICAS), AND BUS TIE BAR (BTB).

Full Narrative

WHILE CRUISING AT FL390, THE AUTOTHROTTLES AND AUTOPILOT DISENGAGED, THE CAPTAIN'S INSTRUMENTS FAILED, AND THE COCKPIT LIGHTING CYCLED ON AND OFF. THE LEFT GENERATOR LIGHT ILLUMINATED, THE EICAS FAILED, A CYCLIC BANGING WAS HEARD, AND AN ACRID ODOR WAS NOTICEABLE. THE LEFT AC BUS AND TRANSFER BUS WERE DEENERGIZED AND THE CAPTAIN ELECTED TO DIVERT TO THE NEAREST SUITABLE AIRPORT. POST INCIDENT INVESTIGATION DISCLOSED A SHORTED DIODE IS THE LEFT GCU (GENERATOR CONTROL UNIT), A DEFECTIVE IDG (INTEGRATED DRIVE GENERATOR), A SHORT IN THE INPUT POWER FILTER IN THE EICAS (ENGINE INDICATOR AND CREW ALERT SYSTEM), AND A DEFECTIVE BTB (BUS TIE BAR).

Flight

Event TypeIncident
Event Time19:15 MST
Nearest Airport0nm N
Runway0
Flight Plan FiledIFR
Aircraft FireNo
Aircraft ExplosionNo

Aircraft

AircraftBoeing 757-222
Tail NumberN508UA
Aircraft CategoryAir
OperatorUnited Airlines
Operating RulePart 121
Engines2
Engine TypeTurbofan
Engine DetailsP&W · 2037-717 · Turbofan · 37000
Seats252

People & Injuries

Injury SummaryNo injuries (47 uninjured)
Fatal0
Serious0
Minor0
Uninjured47
Total47
Crew 1Age 58 · First Class

Conditions

ConditionsVMC
LightDark Night
Wind320° @ 5 kt
Visibility30 sm
CeilingNone
Temperature / Dew Point32 C / 21 C
Altimeter30.00 inHg
Weather SourceWIT

External Links

Appendix: Source Data