Definition
Q-routes are published high-altitude RNAV (area navigation) airways used in the conterminous United States from 18,000 feet MSL up to and including FL 450. They are flown using approved RNAV equipment rather than ground-based VOR navigation, and they appear on en route high-altitude charts with a 'Q' designator (for example, Q-100).
Plain English
Q-routes are high-altitude highways in the sky designed for aircraft using GPS-style navigation instead of older ground-based radio beacons. They run from 18,000 feet up to 45,000 feet and are identified by a 'Q' followed by a number.
Context Anchor
You will see Q-routes on high-altitude instrument en route charts and in instrument flight clearances for aircraft operating in the high-altitude system.
Derivation
The 'Q' is simply a letter designator chosen by the FAA and ICAO to distinguish these RNAV-based high-altitude routes from the older 'J' (jet) routes that rely on VORs. There is no deeper meaning to the letter itself.
Why Pilots Care
They enable more direct and fuel-efficient routing at altitude while reducing dependence on older ground-based navigation aids.
Intuition Check
Do not read the “Q” as an abbreviation with a hidden phrase to expand. Here, Q is simply the identifying letter for this class of published high-altitude route.
Example Sentence 1
ATC cleared the Citation to fly Q-146 from Denver to Kansas City at FL 380.
Example Sentence 2
ATC issued a reroute that replaced several Victor airways with a single Q-route segment above FL350.