On a cross-country flight, how often should you update your altimeter setting?

• A. Every 20–30 minutes
• B. Every 5–10 minutes
• C. Every 60 minutes
• D. Only when ATC requests

Answer: (A)

Keeping the altimeter setting current is essential because the surrounding air pressure changes as you move. Resetting the altimeter to the local pressure setting (QNH) ensures the instrument's reading reflects your true height above mean sea level. If you don’t update, a shift in pressure can make your indicated altitude drift, which can put you too close to terrain or traffic.

Updating every 20–30 minutes is a practical pace that keeps your altitude indication accurate without unnecessary workload. Pressure environments can change fairly quickly on a cross-country trip, especially around weather systems, so this interval helps you stay aware of your actual altitude.

Relying on ATC to request updates isn’t a substitute for keeping your own instrument current; ATC procedures may not cover every change in terrain or airspace, and outdated settings can still lead to errors. Updating more frequently than this is usually unnecessary, while waiting too long increases the chance of a larger altitude discrepancy.