Hence RVSM ends at FL410. Aircraft certified after 1997 actually have tighter altimetry system tolerances. But the airspace structure must accommodate aircraft certified prior to this period. Furthermore, there is really no need to extend RVSM airspace, since airspace in the 40s is relatively empty.

Reduced Vertical Separation Minima (RVSM) is currently limited to the airspace between FL290 and FL410 inclusive. Above FL410 (41,000 feet), vertical separation reverts to the traditional 2,000-foot standard. This restriction exists primarily due to the Altimetry System Error (ASE). At extreme altitudes, air density is significantly lower, making it much harder for standard pressure altimeters to maintain the high degree of accuracy required for 1,000-foot separation. The error budget for avionics increases as the aircraft reaches the upper boundaries of its flight envelope, where small atmospheric fluctuations can lead to larger discrepancies in indicated altitude. Furthermore, few commercial aircraft are certified to operate efficiently above FL410, meaning there is less demand for the increased capacity that RVSM provides. For safety margins, ICAO and the FAA maintain the 2,000-foot buffer to ensure that any altimeter drift or "weight over atmospheric pressure" (W/δ) errors do not result in a mid-air collision in the thin upper atmosphere.