If pressure gauges are not steady, what is the first action to take?

In the event that pressure gauges exhibit instability, the appropriate initial action is to position the UPPER RUDDER and LOWER RUDDER switches to off. This step is crucial because the rudder control system can impact various flight dynamics and systems, including the APU's performance. By disabling these switches, you can prevent further potential complications and help isolate the issue.

This action allows for a safe initial response to assess the situation without risking further damage to the system or affecting other critical components. Once the rudder controls are turned off, you can better analyze the cause of the pressure gauge instability and take subsequent corrective actions as needed.

It's important to remember that other options, such as turning off the APU, closing circuit breakers, or disconnecting external power, may not address the root of the problem as efficiently or safely. Such measures could lead to additional complications or power loss, which may not be necessary right away. Therefore, focusing on the specific controls related to the gauges offers a more targeted approach to troubleshooting the issue effectively.