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NTSB Report
June 12, 1984 · Boeing 747-122 · N4712U
San Francisco, CA
Overview
Report Status
Preliminary report
Event Type
Incident
Date
June 12, 1984
Injury Outcomes
No injuries (4 uninjured)
Location
San Francisco, CA
Aircraft
Boeing 747-122
Tail Number
N4712U
Operator
United Airlines
Injuries
None
Aircraft Damage
Minor
NTSB Number
LAX84IA350
JUST INSIDE THE OUTER MARKER, A 'LOUD BANG' WAS HEARD & LEFT AILERON INPUT WAS NEEDED TO CONTROL ACFT HEADING. THE LANDING WAS MADE WITHOUT INCIDENT UNTIL THE FLAPS WERE RAISED WHILE TAXIING & THE FLT ENGINEER REPORTED A #4 HYDRAULIC SYSTEM FAILURE. THE CAPT LOST BRAKES AND HAD TO UTILIZE STANDBY BRAKES. AT THIS TIME A SPLIT FLAP INDICATION WAS OBSERVED. INSPECTION REVEALED FLAP TRACK FRACTURED APRX 6 INCHES AFT OF THE FORWARD ATTACH POINT. THE FRACTURE INITIATEDON OUTBOARD FLANGE #1 BOLTHOLE WALL BECAUSE OF PITTING CORROSION. A PORTION OF THE FORE FLAP & A SMALL WING PANEL SEPARATED FROM THE ACFT. DURING FLAP RETRACTION AFTER LANDING, THE TRANSMISSION BALL NUT JAMMED. THE DRIVE TORQUE TUBE FRACTURED AT THIS TIME AND THE BROKEN END OF THE ROTATING TORQUE TUBE DAMAGED HYDRAULIC LINES, CAUSING A LOSS OF HYDRAULIC FLUID. AN ALERT SERVICE BULLETIN WAS ISSUED BY BOEING AFTER THIS INCIDENT & UNITED AIRLINES INITIATED A FLEET WIDE INSPECTION.
Full Narrative
JUST INSIDE THE OUTER MARKER, A 'LOUD BANG' WAS HEARD & LEFT AILERON INPUT WAS NEEDED TO CONTROL ACFT HEADING. THE LANDING WAS MADE WITHOUT INCIDENT UNTIL THE FLAPS WERE RAISED WHILE TAXIING & THE FLT ENGINEER REPORTED A #4 HYDRAULIC SYSTEM FAILURE. THE CAPT LOST BRAKES AND HAD TO UTILIZE STANDBY BRAKES. AT THIS TIME A SPLIT FLAP INDICATION WAS OBSERVED. INSPECTION REVEALED FLAP TRACK FRACTURED APRX 6 INCHES AFT OF THE FORWARD ATTACH POINT. THE FRACTURE INITIATEDON OUTBOARD FLANGE #1 BOLTHOLE WALL BECAUSE OF PITTING CORROSION. A PORTION OF THE FORE FLAP & A SMALL WING PANEL SEPARATED FROM THE ACFT. DURING FLAP RETRACTION AFTER LANDING, THE TRANSMISSION BALL NUT JAMMED. THE DRIVE TORQUE TUBE FRACTURED AT THIS TIME AND THE BROKEN END OF THE ROTATING TORQUE TUBE DAMAGED HYDRAULIC LINES, CAUSING A LOSS OF HYDRAULIC FLUID. AN ALERT SERVICE BULLETIN WAS ISSUED BY BOEING AFTER THIS INCIDENT & UNITED AIRLINES INITIATED A FLEET WIDE INSPECTION.
Flight
Event TypeIncident
Event Time21:30 PDT
Nearest Airport0nm N
Runway0
Runway Length0
Runway Width0
Flight Plan FiledIFR
Aircraft FireNo
Aircraft ExplosionNo
Aircraft
AircraftBoeing 747-122
Tail NumberN4712U
Aircraft CategoryAir
DamageMinor
OperatorUnited Airlines
Operating RulePart 121
Engines4
Engine TypeTurbofan
Engine DetailsP&W · JT9D-3 · Turbofan
Seats429
People & Injuries
Injury SummaryNo injuries (4 uninjured)
Fatal0
Serious0
Minor0
Uninjured4
Total4
Crew 1Age 59 · First Class
Conditions
ConditionsVMC
LightDusk
Wind280° @ 25 kt
Visibility15 sm
CeilingNone
Temperature / Dew Point55 / 45 C
Altimeter29.00 inHg
Observation Time03:53
Weather SourceWFAC