Before entering the RVSM flight level band, which altitude measurement capability is required?

• A. Two independent primary altimetry systems
• B. One independent primary altimeter
• C. No altitude measurement requirement
• D. A single altimeter with autopilot

Answer: (A)

RVSM airspace tightens vertical separation to 1,000 feet, so aircraft must have highly reliable and continuously verified altitude information. This is achieved by using two independent primary altimetry systems, providing redundancy so that if one system fails there is a second source of altitude data to rely on. The two systems are typically fed by separate pitot-static sources and are cross-checked by the aircraft’s altitude-keeping logic, which helps detect discrepancies and prevent uncontrolled altitude deviations. Relying on a single altimeter would not meet the safety requirement for RVSM, and the other options either ignore the need for altitude measurement or rely on autopilot alone without the necessary redundancy.