There are specific procedures for checking hydraulic fluid levels in each model of aircraft. These procedures must be followed to make sure the system operates at the required fluid level. Fluid level is generally determined by an indicating device at the system reservoir. The type of indicator used varies with the aircraft model. Sight-glass, gauge, and piston-style indicators are commonly used. There is close tolerance between the operating parts of equipment used in aircraft hydraulic systems and the level of hydraulic fluid contamination; therefore, do not introduce foreign matter into a system being serviced. All servicing must be accomplished by qualified personnel using authorized fluid-dispensing equipment.

The information contained in this section gives general guidance and requirements to follow when fluid servicing hydraulic systems and components. Remember, you need to follow the procedures contained in the applicable technical manuals when you actually service hydraulic systems and components. When you service these systems, use approved fluid-dispensing equipment that is equipped with 3-micron (absolute) filtration. Maintain equipments according to the applicable MIM and MRC. Keep hydraulic fluid dispensing equipment clean. Store it in a clean, protected environment. Service this equipment on a periodic basis, including filter servicing. Protect all fittings or hose ends with approved metal closures when not in use.

Use the correct fluids for each piece of fluid-dispensing equipment, and mark the equipment to indicate the type of fluid. Use the specified hydraulic fluid to service hydraulic systems. Take precautions to avoid accidental use of any other fluid. Do not leave hydraulic fluid in an open container any longer than necessary, particularly in dusty environments. Exposed fluid will readily collect contaminants, which could jeopardize system

performance. With the exception of fluid cans or drums installed in approved dispensing units, open cans of hydraulic fluid are prohibited. Containers for disposal of used fluid must be prominently marked and identified. Empty fluid containers must be destroyed or returned to supply as appropriate.

Do not reuse hydraulic fluid drained from hydraulic equipment or components. Dispose of drained fluid immediately so it wont be accidentally reused. In the event hydraulic fluid is spilled on other parts of equipment on the aircraft, remove spilled fluid using approved wiping materials and dry-cleaning solvent P-D-680.