Equipment for operation in defined airspace with reduced vertical separation minima (RVSM)

An operator shall ensure that aeroplanes operated in RVSM airspace are equipped with:
1. two independent altitude measurement systems;
2. an altitude alerting system;
3. an automatic altitude control system; and
4. a secondary surveillance radar (SSR) transponder with altitude reporting system that can be connected to the alti- tude measurement system in use for altitude keeping.

Source: EU-OPS

See also:
Equipment for operation in defined airspace with reduced vertical separation minima (RVSM)
Operation in defined airspace with reduced vertical separation minima (RVSM)