What is the required operational status of altitude reporting transport for RVSM compliance?

For Reduced Vertical Separation Minimum (RVSM) compliance, it is required that at least one altitude reporting transport system be operational. RVSM is designed to allow aircraft to operate at altitudes where a reduced vertical separation of 1,000 feet can be used between aircraft at altitudes from 29,000 to 41,000 feet. Therefore, having at least one operational altitude reporting system ensures that the aircraft can accurately report its altitude to air traffic control and maintain safe vertical separation from other aircraft.

While both systems being operational offers redundancy and improves safety, the regulatory requirement specifically states that having just one operational system is sufficient for compliance. This allows for flexibility in situations where a backup system may become inoperative, provided that there is at least one functioning system to maintain RVSM standards.