How can altitude be verified when air data readings are unstable in flight?

• A. Cross-check with standby instruments and outside references plus known ground features; maintain safe flight.
• B. Rely on airspeed only.
• C. Use cabin pressure gauge.
• D. Use GPS altitude only.

Answer: (A)

When the air data readings are unstable, you verify altitude using independent references that don’t depend on the pitot-static system. The standby altimeter, which is a mechanical instrument, continues to respond to static pressure changes and provides a reliable backup indication of your altitude. Cross-checking that instrument against what you’re seeing in the cockpit’s primary air data display helps you spot discrepancies and prevent misreadings from leading you off altitude.

In addition, look outside for real-world references: known ground features, terrain elevations, or obstacle heights published on charts and approach plates. If available, GPS altitude can serve as a supplementary check, but it shouldn’t be relied on as the sole source because GPS can have vertical errors or outages. By combining the standby instrument with outside references, you maintain a solid, independent sense of altitude and keep the flight safely above terrain and obstacles.