Turin - The A345/6 has the parking brakes powered by the blue hydraulic system. The parking brake selector valve, when set, acts as a pressure reducing valve and drops the upstream pressure in the brake lines to 175 bar ( 2535 psi ), this being the pressure that holds the brakes on. The system is designed to hold the aircraft with one engine at full power provided the others are all at idle. All this of course pre-supposes that you have ample blue system pressure to start with !