How often should the altimeter difference in-flight be checked?

The correct choice reflects a best practice in aviation safety regarding altimeter checks during flight. Pilots are trained to monitor their altimeter status to ensure they maintain proper altitude. Checking the altimeter difference every hour aligns with standard operating procedures. This interval allows pilots to adjust for changes in barometric pressure and ensure that their altitude readings remain accurate, which is crucial for safe navigation and maintaining appropriate separation from other aircraft. Regular checks of the altimeter help to prevent potential issues, such as altitude deviations that could lead to dangerous situations.

While other intervals may seem reasonable, hourly checks provide a balance between safety and operational efficiency, ensuring pilots stay informed of any significant changes in atmospheric conditions that might affect altitude.