If any of these symptoms sound familiar and you’re certain the thrust reverser (TR) is rigged correctly, then you may want to look at the Flex Shaft Lock. The Flex Shaft Lock is normally at a quiescent state blocking bleed air from reaching the pneumatic drive unit. This is both its purpose and downfall.
Inactive bleed air inevitably leads to carbon deposit and condensation, which in turn leads to corrosion and contamination. Over time this corrosion and resulting contamination finds its way into the TR system where it can wreak havoc.
The Flex Shaft Lock is the first component in the TR bleed air path and contains a filter to help protect it and other components from failure due to contaminants. Over time, the filter will eventually become overwhelmed and not allow full air passage or at all. This can lead to the inability to Stow or Deploy the TR.
The intermittent problems arise when bleed air finds a passage through the plugged filter to Deploy the TR but becomes blocked during Stow.
If you're experiencing these types of problems, it may be a good idea to have the Flex Shaft Lock cleaned, resealed and function-tested.
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