Final answer:
Typically, only state aircraft like military or police services can enter RVSM airspace without required equipment, with ATC approval. Civil aircraft must usually meet stringent equipment standards for RVSM, with exceptions being rare.
Step-by-step explanation:
The aircraft that can enter Reduced Vertical Separation Minimum (RVSM) airspace without the required equipment, with the approval of Air Traffic Control (ATC), generally includes state aircraft such as military, customs, or police services. Civil aircraft, on the other hand, must meet strict equipment requirements to ensure their altitude-keeping performance is precise and reliable. Exceptions for civil aircraft are rare and typically only occur in extenuating circumstances where the safety of a flight could be compromised without access to RVSM airspace.