Definition
A U.S. domestic airspace rule that reduces the vertical separation between aircraft from 2,000 feet to 1,000 feet between flight levels FL290 and FL410 inclusive. To operate in this airspace, both the aircraft and operator must be specifically authorized, with altimetry equipment that meets stricter accuracy and performance standards than those required at lower altitudes.
Plain English
In the high-altitude airspace where airliners cruise, aircraft are allowed to fly only 1,000 feet apart vertically instead of the older 2,000-foot spacing. This lets more aircraft fit into the busy upper altitudes, but only aircraft with very accurate altitude-measuring equipment are allowed in.
Context Anchor
Seen in instrument flying, high-altitude operations, altimeter system discussions, and equipment requirements for aircraft operating in RVSM airspace.
Derivation
‘Reduced Vertical Separation Minimum’ describes exactly what the rule does: it reduces the minimum vertical distance required between aircraft. ‘Domestic’ marks it as the U.S. version of the international RVSM standard. The ‘minimum’ refers to the smallest legal spacing allowed — not a target, but a floor.
Why Pilots Care
Allows aircraft to access more usable flight levels, improving routing options, fuel efficiency, and airspace capacity.
Intuition Check
Reduced does not mean less strict. It means the allowed vertical spacing is smaller, so the equipment and altitude-keeping requirements are stricter.
Example Sentence 1
Before climbing to FL350, the crew confirmed the aircraft was DRVSM-authorized and that both altimeters agreed within tolerance.
Example Sentence 2
DRVSM procedures permit 1,000-foot separation between FL 330 and FL 340 for approved operators.