How many air data computers are required for RVSM operations?

• A. Two
• B. One
• C. Three
• D. Zero

Answer: (A)

RVSM operations hinge on having trustworthy and cross-checked altitude information, because the reduced vertical separation of 1000 ft means even small errors can lead to unsafe situations. Air data comes from pitot-static sensors that feed into air data computers, which derive altitude and other flight parameters used by the autopilot/flight guidance and the vertical separation management.

Having two independent air data computers provides the necessary fault tolerance. Each computer processes the same air data independently and their outputs are cross-checked. If one computer or its data starts to drift, the system can detect the discrepancy and rely on the other, maintaining accurate altitude information and safe operation. This redundancy is the minimum requirement to meet RVSM reliability standards.

Using just one computer would leave no redundancy for a fault, risking incorrect altitude indication and potential loss of RVSM capability. While some aircraft may have more than two computers for other reasons, the standard requirement specifically calls for two.