Someone asked, Parking brake powered by hydraulic; and hydraulic power is supplied by Engine; but when all engines shutdown, how would the Parking Brake maintain the hydraulic pressure?
In a A330, there is 3 hydraulic system(Green, Yellow and Blue) for redundancy. (it differs from from different aircraft type and design.)
In general, there is couple hydraulic pressure source: 1. From the Engine Driven Pump; 2. Electric pump; 3. Brake Accumulator (NOT really a source, but like a pressure holder); 4. RAT ram air turbine.(some aircraft design)
Normally, Hydraulic Pressure will be provide by the engine driven pump. And while the Engine is running, the engine driven pump will pressurized the system, and (in blue system) the brake accumulator(yellow circle) will maintain pressure within the accumulator. When the engine is off, brake accumulator pressure with provide the pressure for the parking brake.
Don't confuse with the accumulator (orange circle) those are not for brake pressure. Those are designed to help maintain constant pressure by covering transient demands during normal operation.
Comment below if you have any questions/ doubts/ wonders/ even complaint lol
Detail explanations, thanks a lot! Just a small question, as I saw from the FCOM description of the parking brake, it does have a time limit for the brake accumulator to provide sufficient hydraulic pressure for the parking brake. However, if a situation like the long term parking aircraft in VHHH now. They have to park for way more than 12 hours. Without starting an APU or supplies of ground electrical power to drive the electric hydraulic pump, does the aircraft only rely on the wheel chocks for holding them still?
Besides, quite curious about the triple indicator on Airbus aircraft, which three brake systems is indicated on the triple indicator and when do we need to read the indications on it?