If you find a vacuum-operated instrument glass loose, what should you do?

When dealing with a vacuum-operated instrument that has a loose glass, the best course of action is to install another instrument. This is because a loose glass can lead to inaccuracies in the instrument readings, which can ultimately affect safety and operational performance. If the glass is not securely fitted, it may allow dirt, moisture, or other contaminants to enter the instrument, potentially leading to malfunction or failure.

Installing another instrument ensures that the equipment is functioning correctly and reliably, adhering to safety standards. It's crucial in aviation to maintain precise and accurate instruments, as any error could have significant implications during flight operations.

Other options such as attempting to secure it with adhesive, leaving it as is, or adjusting the vacuum pressure do not address the fundamental issue of the instrument being unsafe or unreliable, making them inappropriate courses of action in this situation. Ensuring that instruments are in optimal condition is vital for effective monitoring and control during flight.