Aviation safety investigations & reports

Assistance to the Civil Aviation Safety Authority in the examination of a cracked control cable terminal

Investigation number:
AE-2015-020
Status: Completed
Investigation completed

Report

The Civil Aviation Safety Authority (CASA) released Airworthiness Directive AD/GEN/87 Primary Flight Control Cable Assembly Retirement in February 2015 which required the retirement of control cable assemblies after 15 years in service. Following the release of the AD, CASA received a service difficulty report where a cable terminal fitting exhibited cracking after less than 10 years in service. As the cable exhibited cracking prior to the retirement life stated in the AD, it was requested that the Australian Transport Safety Bureau (ATSB) examine the terminal to determine the mode of failure, and if it was the same mechanism as that described in the AD.

The submitted terminal exhibited four longitudinal cracks extending approximately 5mm from the end of the terminal. Small indentations were identified on either side of two of the cracks on opposite sides of the terminal. These were considered to be an artefact of the swaging process. The location and orientation of the cracking was different to those of the terminals examined previously as part of investigation AE-2012-028. There was no evidence of the highly branched cracking that was seen in other examples and which is normally associated with stress corrosion cracking.

The cracking on the submitted terminal likely initiated as a result of the mechanical damage that occurred during the manufacturing process. The terminal has been returned to CASA, who are continuing their investigations into the origin of the terminal and the mechanical damage.

Figure 1: Terminal submitted to the ATSB, crack location arrowed
Terminal submitted to the ATSB, crack location arrowed

Source: ATSB

Figure 2: Magnified view of terminal, showing the mechanical damage either side of the crack
Magnified view of terminal, showing the mechanical damage either side of the crack

Source: ATSB

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General details
Date: 12 February 2015   Investigation status: Completed  
  Investigation level: Defined - click for an explanation of investigation levels  
Location   (show map): ATSB Central Office    
State: Australian Capital Territory   Occurrence type: Flight control systems  
Release date: 08 September 2015   Occurrence class: Technical  
Report status: Final   Occurrence category: Other  
  Highest injury level: None  
Last update 14 November 2018