What is the minimum amount of slack that must be left when a flexible hose is installed in an aircraft hydraulic system?

• A. The hose should be at least 1% longer than the distance between fittings.
• B. The hose should be at least 5% longer than the distance between fittings.
• C. The hose should be 10% longer than the distance.
• D. The hose should be exactly the distance between fittings.

Answer: (B)

The minimum slack is about 5% longer than the distance between fittings. This extra length provides room for movement, vibration, and thermal expansion so the hose won’t become taut or kink under normal operation. In an aircraft hydraulic system, components can shift slightly and fluids heat up, causing expansion; a little extra length lets the hose flex without placing stress on fittings or abrading the hose. For example, if the fittings are 20 inches apart, you’d leave about 1 inch of slack. Too little slack (like 1% or no slack) can lead to strain and failure; too much (like 10%) can create routing issues or unnecessary slack.