Boeing 747-251B N628US

Summary

On 5 January 1996 at about 20:30 local time, a Boeing 747-251B registered N628US was involved in an incident near Los Angeles, California, United States. 385 people were on board and nobody was injured. The aircraft was slightly damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

5 January 1996 at 20:30

Classification

Incident

Location

Los Angeles, California, United States

Coordinates

33.9510, -118.4009

Aircraft

Boeing 747-251B

Registration

N628US

Category

Airplane

Engines

4

Operator

Not recorded

Operating rule

Part 121: Air Carrier

Purpose of flight

Unknown

Phase of flight

Not recorded

Route

Unknown → Tokyo

Aircraft damage

Minor

Weather

VMC

Light

Day

NTSB number

LAX96IA087

Nobody was injured.

The fatigue fracture of the number 4 bearing oil pressure tube due to an improper maintenance cleaning procedure by company maintenance personnel.

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

As the aircraft climbed through 11,500 feet msl the number 2 engine sustained an uncontained failure of the low pressure turbine section. Following engine shutdown, the crew dumped 147,000 pounds of fuel and returned to Los Angeles, for an uneventful landing. Postaccident inspection of the aircraft revealed a 2-foot hole in the number 2 engine cowl turbine area at the 9 o'clock position. Minor dents were noted on the number 1 engine cowl, pylon, and the underside of the left wing. Several fan blades from the number 1 engine were found with nicks and leading edge damage. Disassembly of the engine revealed that the oil pressure line to the number 4 bearing had fractured, with evidence of oil spray and fire signatures on the 6th stage low pressure turbine disk. Measurements of the 6th stage disk disclosed disk growth about 1.06 inches over blueprint maximum, which liberated all 6th stage blades from the disk. Metallurgical examination of the tube fracture revealed a fatigue crack through about 25 percent of the tube circumference, with origins at spiral scratches found on the inside diameter of the tube. Periodically the tube must be cleaned of coke build-up. Northwest Airlines and Pratt & Whitney maintenance/overhaul documents relating to the overhaul and cleaning of the number 4 bearing internal pressure tube assembly specify a an oven baking procedure. Cautionary notes state that wire brushes or reamers are not to be used for internal cleaning of the tubes.

Quoted verbatim from the NTSB record.