Boeing 757-251 N512US

Summary

On 9 October 1989 at about 18:45 local time, a Boeing 757-251 registered N512US, operated by Northwest Airlines, was involved in an incident near San Francisco, California, United States. 147 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

9 October 1989 at 18:45

Classification

Incident

Location

San Francisco, California, United States

Coordinates

37.7998, -122.3995

Aircraft

Boeing 757-251

Registration

N512US

Category

Airplane

Engines

2

Operator

Northwest Airlines

Operating rule

Part 121: Air Carrier

Purpose of flight

Unknown

Phase of flight

Not recorded

Route

Detroit → Unknown

Aircraft damage

Minor

Weather

VMC

Light

Day

NTSB number

CHI90IA006

Nobody was injured.

THE EXTREME WEAR AND EVENTUAL FAILURE OF A TORQUE TUBE IN THE INBOARD TRAILING EDGE FLAP SYSTEM. INSPECTION AND LUBRICATION INTERVALS WERE A FACTOR, AS WAS THE PHYSICAL LOCATION OF THE TORQUE TUBE WITH REFERENCE TO EXTERNAL FACTORS.

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

Read the full NTSB narrative

THE FLIGHT CREW REPORTED THAT THEY RECEIVED A 'FLAP DISAGREE' MESSAGE DURING THE DESCENT AND APPROACH TO THEIR DESTINATION AIRPORT. WHEN CHECKLIST PROCEDURES WERE NOT SUCCESSFUL IN CORRECTING THE SITUATION, AN UNEVENTFUL 'ABNORMAL FLAP' LANDING WAS PERFORMED. POST-INCIDENT INSPECTION REVEALED A FAILED INBOARD TRAILING EDGE FLAP DRIVE TORQUE TUBE COUPLING. FURTHER INVESTIGATION REVEALED ONE SIMILAR FAILURE, AND EXAMINATION OF THE OPERATING 757 FLEET REVEALED NUMEROUS OCCURRENCES OF EXCESSIVE WEAR ON THE AFT COUPLING OF THE TORQUE TUBE ASSEMBLY. LAB ANALYSIS OF THE WEAR, AND A METALLURGICAL EXAMINATION RESULTED IN THE MANUFACTURER REDUCING THE RECOMMENDED MAINTENANCE INTERVAL AND RECOMMENDING MORE FREQUENT VISUAL INSPECTIONS OF THE COMPONENT.

Quoted verbatim from the NTSB record.