NTSB Identification: LAX84IA350.
The docket is stored on NTSB microfiche number 25003.
Scheduled 14 CFR operation of UNITED AIRLINES
Incident occurred Monday, June 11, 1984 in SAN FRANCISCO, CA
Aircraft: BOEING 747-122, registration: N4712U
Injuries: 4 Uninjured.

NTSB investigators used data provided by various sources and may not have traveled in support of this investigation to prepare this aircraft incident report.

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.

The National Transportation Safety Board determines the probable cause(s) of this incident to be:

FLIGHT CONTROL,FLAP ATTACHMENT..CORRODED

The National Transportation Safety Board determines the probable cause(s) of this incident to be:

FLIGHT CONTROL,FLAP ATTACHMENT..FATIGUE


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