the master cylinder. Power brake systems use utility ormain hydraulic system pressure from the aircraft. Thepower brake systems allow for higher brake linepressures than can be obtained with the independentsystem.INDEPENDENT-TYPE BRAKE SYSTEMThe depth of independent brake system mainte-nance allowable at the intermediate and organizationallevels of maintenance varies with the complexity of thecomponents. System maintenance at the organizationallevel generally consists of servicing, troubleshooting,parts replacement, and “on aircraft” repairs. Bleeding ofthe brake system is discussed later in this chapter.Reservoir maintenance is limited to servicing,removal, repair, parts replacement, testing, andinstallation. Servicing of the reservoir requires thatfiltered hydraulic fluid be gravity fed into the reservoirthrough the filler opening until the sight gauge indicatesit is full. The reservoir should not be overfilled. The areaaround the filler neck should be cleaned before youremove the filler plug to prevent any form ofcontamination from being introduced into the reservoirand the brake system. Maintenance of the reservoir, themaster brake cylinder, and the brake assembly isdiscussed later in this chapter.As with other systems, a troubleshooting chart is fur–nished in the MIM for use in troubleshooting/ analyzingmain landing gear wheel and independent brake systemmalfunctions. Chapter 3 of this training manual containsexamples of troubleshooting tables and charts.POWER-TYPE BRAKE SYSTEMOrganizational maintenance of the power/manualbrake system consists of checking system operation,system adjustment, isolating malfunctions, andreplacement and adjustment of system components. Seefigure 12-35. The checkout procedures in most MIMsare provided for use during established inspections orfor use in performing trouble analysis.GENERAL BRAKE SYSTEMMAINTENANCEProper functioning of the brake system is of theutmost importance. Inspections must be performed atfrequent intervals, and maintenance work must beperformed promptly and carefully.Operational ChecksPrepare the aircraft for an operational checkout byinstalling the landing gear down locks, jacking theaircraft to provide proper ground clearance for thelanding gear, and applying external electrical power.Placing the antiskid switch in the OFF position shouldilluminate the antiskid warning light. When the landinggear handle is moved to the UP position, the antiskidlight should go out. At this point, external hydraulicpower is slowly applied to the utility system. The wheelsshould not rotate. By placing the landing gear handle tothe DOWN position, it should illuminate the antiskidlight and free the wheels to rotate. The brake pedalsshould be fully depressed to apply the brakes a minimumof three times.With external hydraulic and electrical powerremoved from the aircraft, operationally check theemergency system by pulling the emergency brakehandle. The wheels should not rotate when the handle ispulled. Releasing the handle should immediately releasethe brakes. If any portion of the operational or functionaltest does not meet the results specified in the MIMs,refer to the trouble analysis sheets for the brake system.Functional TestsPrepare the aircraft for a complete functionalcheckout by installing the landing gear down locks,jacking the aircraft to provide ground clearance for thelanding gear, installing pressure gauges in the wheelbrake assembl y’s bleed ports, and applying externalelectrical and hydraulic power.When the antiskid switch is in the OFF position, theantiskid warning light will illuminate. Move the landinggear handle to the UP position, which will cause theantiskid warning light to go out. The gauges on the brakeassemblies should indicate 650 to 1,000 psi. Place thelanding gear handle to the DOWN position to illuminatethe antiskid warning light. The brake gauges shouldindicate a maximum of 75 psi, and the wheels should befree to rotate.Remove electrical power from the aircraft. Depressthe brake pedals several times to check braking action.Place a bubble protractor on the brake pedals and adjustto zero when the brakes are in the OFF position. Whenthe brakes are fully depressed, the protractor shouldindicate 30 degrees ±1 degree, and the hydraulic gaugeson the brake assemblies should indicate the samepressure as the external hydraulic power source.The external hydraulic power is shut down andsystem pressure is relieved by operating the rudderpedals. Check brake accumulator action by fullydepressing the brake pedals several times and checkingthe brake assembly action. Check the emergency brakesystem in the same manner as described for theoperational checkout.12-41
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