What is a requirement for aircraft under Reduced Vertical Separation Minimum (RVSM)?

Under Reduced Vertical Separation Minimum (RVSM), one key requirement is that aircraft must be equipped with two independent altitude measurement systems. This requirement is critical because RVSM allows aircraft to operate at altitudes where the vertical separation between them is reduced from 2,000 feet to 1,000 feet.

Having two independent altitude measurement systems ensures that there is a reliable backup in case one system fails, significantly enhancing the safety and accuracy of altitude reporting. Accuracy in altitude measurement is essential for safe separation between aircraft in RVSM airspace, as any discrepancies could lead to potential midair collisions.

Other choices, while possibly relevant to different regulatory or operational aspects, do not meet the specific requirement for RVSM. For example, one altimeter system alone does not provide the necessary redundancy for safety. Similarly, a transponder with mode A does not pertain directly to altitude measurement, and an automatic speed control system, while useful for maintaining flight parameters, does not address altitude accuracy or reporting necessary under RVSM regulations.