Plain English Meaning

A rule that lets aircraft fly closer together vertically — 1,000 feet apart instead of 2,000 feet — at high cruising altitudes. Only aircraft with the right equipment and approval can use this airspace.

Full Definition

An air traffic control standard that reduces the required vertical spacing between aircraft from 2,000 feet to 1,000 feet in the airspace between FL290 (29,000 feet) and FL410 (41,000 feet) inclusive. To operate in this airspace, aircraft must meet specific altitude-keeping equipment requirements, the operator must hold an RVSM authorization, and pilots must be trained in RVSM procedures.

Context Anchor

Seen in instrument flight planning, high-altitude enroute operations, and discussions of aircraft approval for flight above about 29,000 feet.

Derivation

The phrase is descriptive: 'reduced' (less than before), '' (the up-and-down spacing between aircraft), and '' (the smallest amount). It signals a tightening of the older 2,000-foot rule into a 1,000-foot rule.