What is RVSM?

Background 
Because the accuracy of standard pressure altimeters decreases with altitude, increased vertical separation is required at higher altitudes to preserve risk margins. Accordingly, in 1958 ICAO introduced a minimum vertical separation standard of 2000 feet above FL290.  So, all usable cruising levels utilising standard vertical separation above FL290 have odd values. The flight levels FL310, 350, and 390 are used only for southerly (NZ domestic) or westerly (oceanic) cruising levels, and FL330, 370, and 410 for northerly or easterly tracks. There are no even-numbered flight levels available for level cruising flight using standard vertical separation above FL290.

As traffic volumes increased, studies began into how this standard could be reduced to 1000 feet for traffic capacity enhancement. By the 1990s, ground and airborne technology had improved to the extent that such a reduction became feasible, and airspace around the world progressively introduced this reduced separation standard.

Reduced vertical separation minima (RVSM) airspace now covers nearly all global airspace between FL290 and FL410 inclusive, and nearly all modern jet airliners are approved to operate under RVSM. If you plan to fly within these flight levels, the RVSM applies. If your aircraft is not equipped for RVSM, you are unlikely to receive a clearance above FL290, because ATC will also need to apply standard separation to any aircraft in your vicinity irrespective of their RVSM status if so cleared. Some countries may ban non-RVSM aircraft above FL290, but that is not, in itself, an RVSM requirement. Provided there are no aircraft in your vicinity within 2000 feet above and below you, and the State's local rules allow, flight by non-RVSM aircraft into RVSM airspace is possible.

If you plan to fly south in the NZZC (NZ Domestic) FIR or west in the NZZO Oceanic FIR, RVSM cruising levels are FL300, FL320, FL340, FL360, FL380 and FL400.

Cruising levels available under RVSM for north tracks in the NZZC FIR or east in the NZZO Oceanic FIR are FL310, FL330, FL350, FL370, FL390 and FL410.

Above FL410, RVSM does not apply, and vertical separation reverts to a minimum of 2000 feet with only odd-numbered flight levels. Thus, FL420 is not a valid cruising level anywhere globally, and you cannot plan to fly at that altitude. This error is common on VATSIM, however, you may only operate in level flight at FL420 with a “block” altitude clearance.

For more information on RVSM procedures - please visit the New Zealand AIP -  ENR1.1, Page 23.  ATS Airspace Classification may also prove to be an interesting read, available from the New Zealand AIP - ENR1.4.