In RVSM operations, how many Air Data Computers must be operational?

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

Answer: (B)

In RVSM operations, reliability of altitude information is crucial because aircraft operate with a tight vertical separation. The Air Data Computer provides the essential air data, including pressure altitude, to the flight control and navigation systems. To avoid a single point of failure affecting altitude accuracy, at least two independent Air Data Computers must be operational so they can cross-check each other and maintain correct altitude data if one unit fails. Having two working ADCs allows the system to keep reliable altitude information even in the presence of a fault, whereas relying on only one ADC removes that redundancy and isn’t acceptable for RVSM. If more than two ADCs are installed, they can all contribute, but the minimum required is two, which is why two is the correct requirement.