What happened
During normal braking operations following a landing, the right brake disc of VH-PPDO experienced a structural failure. The component was found to be severely corroded, which compromised its ability to withstand operational loads. While the failure did not result in no injuries or additional damage to the aircraft, the breakdown of the braking system presented a risk of runway excursions or collisions with other surface movements.
The investigation
The investigation focused on the condition of the Rapco brake disc installed on the Sling LSA. It was determined that this specific part was not approved by the aircraft manufacturer for use on this model, meaning the suitability of the replacement part had not been verified. Although the materials used were similar to the original Matco components, the disc featured an electroless nickel barrier coating. This type of coating is susceptible to corrosion if the plating becomes discontinuous at any point.
Investigators noted that VH-PPDO was frequently parked outdoors in a saltwater-proximate environment, which likely accelerated the degradation. This environmental impact was also evident in the brake assemblies of six other aircraft within the same fleet. Because the exact date of the disc's installation was unknown, the precise duration of the corrosion process could not be determined.
Findings
- The primary cause of the failure was that the corrosion on the brake disc assembly was not identified by the operator or maintenance provider as having reached a level that threatened the component's structural integrity.
- The installed Rapco brake disc lacked manufacturer approval for fitment to the Sling LSA.
- Maintenance and daily pilot inspections failed to detect the progression of the corrosion.
- The maintenance organisation was aware that corrosion was present but did not implement actions to address its advancement.