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Casualties unknown

Separation of Right Wing #3 Leading Edge Slat During Descent (N124AA)

Dfw Airport, TX, US

On September 15, 1984, a Mcdonnell Douglas DC-10-10 (registration N124AA) was involved in an aviation accident near Dfw Airport, TX. Investigators recorded the probable cause as: Installation of a phenolic pulley (P/N 1969-172) in place of the required aluminum pulley (P/N 1969-132) on the #3 leading edge slat, which led to overload failure due to flight loads exceeding the design limit of the phenolic pulley. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.

Sourcesthe U.S. National Transportation Safety Board (NTSB) historical archivePrimary reportUpdated 2026-06-10Data APIEditorial standards
Aircraft registered N124AA
Aircraft registered N124AA. Photo: Glenn Beltz from Goleta, USA / CC BY 2.0, via Wikimedia Commons

A DC-10 experienced separation of the right wing #3 leading edge slat during approach. Investigation found an incorrect pulley installed during a C-check led to overload failure.

Incident Description

During descent for approach, the right wing #3 leading edge slat separated from the aircraft. The incident occurred on a DC-10 operated by an unspecified airline.

Maintenance History

On July 5, 1984, the aircraft underwent a C-check inspection. During this maintenance, a retract aluminum pulley for the #3 leading edge slat (part number 1969-132) was replaced with a phenolic pulley (part number 1969-172).

Investigation Findings

Metallurgical examination of the failed pulley and cable revealed evidence of overload failure. The DC-10 Parts Illustrated Catalogue specifies that an aluminum pulley must be installed on the #3 leading edge slat, as flight loads on that slat exceed the design load of the phenolic pulley. The incorrect pulley installation was identified as the cause of the failure.

Fleet Inspection

Inspection of other company DC-10 aircraft found at least three additional airplanes with phenolic pulleys installed in the #3 slat position.

Probable cause

Installation of a phenolic pulley (P/N 1969-172) in place of the required aluminum pulley (P/N 1969-132) on the #3 leading edge slat, which led to overload failure due to flight loads exceeding the design limit of the phenolic pulley.
Maintenance error

More accident analyses

Investigation report by the U.S. National Transportation Safety Board (NTSB) historical archive. Original record: https://carol.ntsb.gov/event/20001214X41063. This page is a structured re-presentation; facts and quotes are in the National Transportation Safety Board (NTSB), United States.