What operational equipment must an aircraft have to maintain altitude in RVSM airspace?

In Reduced Vertical Separation Minimum (RVSM) airspace, maintaining altitude accurately is crucial for aircraft safety due to the reduced vertical separation between aircraft flying at the same altitude. An operational autopilot with altitude hold capability is essential because it ensures precise altitude maintenance, reducing the risk of altitude deviations. This is particularly important in RVSM airspace where even small altitude differences can lead to unsafe situations.

The use of an operational autopilot with altitude hold allows for continuous monitoring and maintaining of altitude with high accuracy, which assists in meeting the stringent requirements set by aviation authorities for aircraft operating in RVSM environments. This capability is critical for ensuring compliance with altitude regulations, thereby enhancing safety during flight operations.

Other options, while they may contribute to flight operations in general, do not fulfill the specific requirements needed to maintain altitude consistently and accurately in RVSM airspace.