Which of the following rules is basic to aircraft hydraulic servicing?

Maintaining a high state of cleanliness is vital in aircraft hydraulic servicing because contamination can lead to system failures, decreased performance, and potentially hazardous situations. Hydraulic systems are sensitive to particulates and moisture that can impair function, cause corrosion, or lead to pump failure. Ensuring that all tools, containers, and transfer equipment are clean reduces the risk of introducing contaminants into the hydraulic system. This practice not only extends the life of the hydraulic components but also ensures the safety and reliability of the aircraft during operation. Proper cleanliness standards include using approved hydraulic fluids, keeping servicing areas organized, and using clean, closed containers whenever possible to minimize exposure to contamination.