In what phase of flight is the static system leakage check required to be performed?

The static system leakage check is a crucial procedure performed to ensure the integrity of the aircraft's static pressure system, which affects altimeters, airspeed indicators, and vertical speed indicators. This check is required to be conducted before a flight operation, as it confirms that the static system is functioning correctly and will provide accurate readings throughout the flight.

By performing this check prior to flight, pilots can ensure that any potential leaks are identified and addressed before takeoff, thereby enhancing safety and reliability during the subsequent phases of flight. Conducting the leakage check before operating the aircraft allows for corrective actions to be taken if any issues are discovered, ensuring that all instruments will perform as expected in-flight.