Plain English Meaning

It's a note added to a flight plan that tells air traffic control the aircraft is not approved to fly in the high-altitude airspace where planes are kept just 1,000 feet apart vertically. The controllers will then keep the aircraft below or outside that airspace.

Full Definition

A flight plan remarks entry used in the ICAO flight plan format to indicate that an aircraft is not approved to operate in airspace where Reduced Vertical Separation Minimum (RVSM) applies. RVSM airspace, generally between FL290 and FL410, requires aircraft and crews to be specifically certified to maintain 1,000 feet of vertical separation. Filing STS/NONRVSM tells ATC that the aircraft cannot legally fly within this airspace and must be routed around or below it.

Context Anchor

Seen in ICAO flight plan entries, especially when planning a flight that may involve high-altitude airspace where RVSM rules apply.