P-8A Poseidon – Operating Limitations Practice Exam

The main idea here is that RVSM altitude accuracy relies on two independent primary pressure-altitude measurement systems that are used continuously to maintain the required 1000 ft vertical separation. The standby altimeter is only a backup instrument; it isn’t part of the normal altitude-keeping loop and isn’t required to meet the same RVSM accuracy standards as the primary systems. That’s why it does not meet the RVSM accuracy requirements in the sense used for active RVSM operation. The primary altimeters are the ones that must meet the RVSM accuracy criteria, with the barometric altitude sensors providing the data to support those primaries. GPS altitude sensors are not used for RVSM altitude maintenance and are not certified to meet those barometric RVSM accuracy standards, which is why they aren’t considered meeting the requirements.