What is the maximum duration the standby hydraulic pump might operate when applying external or APU power?

The maximum duration that the standby hydraulic pump can operate when using external or APU power is 4 seconds. This limitation is designed to prevent overheating and potential damage to the pump if it operates beyond that duration. During situations where the standby hydraulic system is required, such as in emergencies or loss of primary hydraulic pressure, this time frame allows for quick and effective support of critical flight controls or systems. Understanding this limit is essential for pilots to manage hydraulic systems correctly and to ensure safety during operations that may necessitate the use of auxiliary hydraulic power.