# NTSB LAX84IA350: Boeing 747-122, N4712U, San Francisco, CA, June 12, 1984

- Type: NTSB incident investigation
- Classification: Incident · No injuries · Incident investigation · Final report
- Date: June 11, 1984, 21:30 local (Jun 12, 1984, 04:30 UTC)
- Place: San Francisco, CA
- Coordinates: 37.609416, -122.379501 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=37.6094&lon=-122.3795&mi=10
- Phase of flight: [Approach](https://openairdocs.org/ntsb-phases/500) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 4 uninjured
- Status: Completed
- Report: Approved by Office Director
- NTSB case key (mKey): 24044
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=LAX84IA350
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/24044/pdf
- Page: https://openairdocs.org/ntsb/LAX84IA350

## Sequence of events

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

- Airframe/component/system failure/malfunction, approach
  - flight control,flap attachment - corroded (cause)
  - flight control,flap attachment - fatigue (cause)
  - hydraulic system,line - leak
  - landing gear,normal brake system - inoperative

## Analysis

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.

## Aircraft

- Registration: N4712U (not matched to a registry record)
- Reported make and model: BOEING 747-122
- Category: Airplane
- Serial number: 19757
- Airframe hours: 45436
- Engines: P&W JT9D-3 turbo fan
- Damage: Minor damage
- Flight: Part 121
- Operator: United Airlines
- Registered owner: Banker Trust Co. Trustee
- Airworthiness certificate: Standard, Transport
- Last inspection: AAIP, January 27, 1984, 1,178 hours before
- Departed: HNL, HONOLULU, HI
- Destination: SFO, SAN FRANCISCO, CA
- Flight plan: IFR

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 59; airline transport; airplane ratings: multi-engine land; instrument ratings: airplane; medical: class 1, valid medical--w/ waivers/lim; seat: left; flight hours: 31,140 total

## Weather

- Conditions: Visual (VMC), Dusk
- Wind: 280° at 25 knots
- Visibility: 15 statute miles
- Lowest ceiling: none
- Temperature: 55 °F, dew point 45 °F
- Altimeter: 29.00 inHg
- Observed at: SFO, 5 nm away

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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