What indicates the reliability of gyro instruments?

The reliability of gyro instruments is indicated by checking the suction gauge is in the green. Gyro instruments, such as the artificial horizon and heading indicator, rely on a vacuum or pressure source to operate properly. The suction gauge measures the vacuum or pressure being applied to these instruments, and a reading within the green arc signifies that the system is functioning correctly and providing adequate power to the gyros.

A reading outside of the green range indicates a potential malfunction, which could lead to instrument failure. Continuous operation without issues, while important, does not provide an immediate indication of reliability like the suction gauge does. Additionally, fluctuations in the readings or null readings would suggest that there is a problem with the instrument, making the suction gauge check the most direct indicator of reliability.