FlightFinder
Check my flight
No fatalities

Flap Disagree Message During Descent Leads to Abnormal Landing; Failed Torque Tube Coupling Found (N512US)

San Francisco, CA, US

On October 9, 1989, a Boeing 757-251 (registration N512US) operated by Northwest Airlines was involved in an aviation accident near San Francisco, CA. No fatalities were reported. Investigators recorded the probable cause as: 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. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive; 12 related events involving the same aircraft type or operator are linked below.

Sourcesthe U.S. National Transportation Safety Board (NTSB) historical archivePrimary reportUpdated 2026-07-04Data APIEditorial standards
Boeing 757-251
Photo: Ryanmac06 at English Wikipedia / Public domain, via Wikimedia Commons

A flight crew received a flap disagree message during descent. After checklist procedures failed, they performed an abnormal flap landing. Inspection revealed a failed inboard trailing edge flap drive torque tube coupling. Investigation found similar failures and wear on the 757 fleet.

Incident Description

A flight crew reported receiving a flap disagree message during the descent and approach to their destination airport. After attempting the associated checklist procedures without success, the crew performed an uneventful abnormal flap landing.

Post-Inspection Findings

A post-incident inspection revealed a failed inboard trailing edge flap drive torque tube coupling. Further investigation identified one similar failure in the fleet, and an examination of the operating 757 fleet discovered numerous occurrences of excessive wear on the aft coupling of the torque tube assembly.

Laboratory Analysis and Manufacturer Actions

Laboratory analysis of the wear and a metallurgical examination led the manufacturer to reduce the recommended maintenance interval and to recommend more frequent visual inspections of the component.

Related events

Same aircraft family

Same operator

More Boeing 757 safety records →

All Boeing 757-200 accidents →

Frequently asked questions

What happened in the 9 Oct 1989 Boeing 757-251 accident near San Francisco, CA?

A flight crew received a flap disagree message during descent. After checklist procedures failed, they performed an abnormal flap landing. Inspection revealed a failed inboard trailing edge flap drive torque tube coupling. Investigation found similar failures and wear on the 757 fleet.

Were there any fatalities in the 9 Oct 1989 Boeing 757-251 accident?

No fatalities were recorded in this accident.

What aircraft was involved and where did it happen?

The accident on 9 Oct 1989 involved a Boeing 757-251, registration N512US, operated by Northwest Airlines, at San Francisco, CA.

What was the probable cause of the accident?

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.

More accident analyses

Investigation report by the U.S. National Transportation Safety Board (NTSB) historical archive. Original record: https://carol.ntsb.gov/event/20001213X29555. This page is a structured re-presentation; facts and quotes are in the National Transportation Safety Board (NTSB), United States.