Final answer:
A flexible hose installed in an aircraft's hydraulic system should have enough slack to allow for a slight bend, often referred to as a 'service loop', to avoid excessive wear and potential failure from vibration and thermal expansion. Specific guidelines depend on the aircraft manufacturer and hose type.
Step-by-step explanation:
The minimum amount of slack that must be left when a flexible hose is installed in an aircraft hydraulic system varies depending on specific aircraft manufacturer guidelines and the type of hose being used. However, a general rule of thumb is that a hose should not be stretched tight between two fittings, as this can cause excessive wear and failure due to vibration and thermal expansion. Typically, the slack should allow for a slight bend in the hose, often referred to as a 'service loop'. It's essential that the installation accounts for all conditions the hose will encounter, such as pressure, temperature changes, and potential movements of the components it connects. Adhering to the specific aircraft's maintenance manual and the hose manufacturer's guidelines is crucial for proper installation.