What occurs when the AAN LT switch is set to TEST?

When the AAN LT switch is set to TEST, all flight deck annunciator lights illuminate. This function is a part of the annunciation system's self-test procedure, which is crucial for ensuring that pilots can verify the operational status of warning and caution lights on the flight deck. By illuminating all annunciator lights, the system allows for a visual confirmation that each light is functioning correctly.

This self-test is important for maintaining safety and operational readiness, as it ensures that any malfunctioning lights can be identified before takeoff. The illumination of cockpit lights or other parameters does not represent the full scope of the AAN LT switch's testing capability, as the primary purpose is to verify the status of all the annunciator lights in the cockpit.