How long must the manual parking brake release button be pushed to release pressure?

The manual parking brake release button must be held for 30 seconds to ensure proper release of pressure. This duration is designed to allow the hydraulic system adequate time to vent any residual pressure, thereby ensuring that the aircraft can safely disengage the parking brake mechanism. This is critical for maintaining operational safety, as improper or insufficient release may lead to complications during taxiing or takeoff. Understanding the specific time requirement helps pilots and ground crew effectively manage the aircraft's braking system, emphasizing the importance of adhering to the manufacturer’s guidelines in operational procedures.