Definition
The vertical division of an Air Route Traffic Control Center (ARTCC) airspace block into two altitude bands, each worked by a different controller. The low sector handles traffic below a defined altitude (often around FL240, but it varies by Center), and the high sector handles traffic at and above that altitude. Each sector has its own radio frequency and controller responsible for separation and traffic flow within that altitude band.
Plain English
ARTCC airspace is split into upper and lower slices. One controller works the lower slice, another works the upper slice, and they each have their own frequency. Which one you talk to depends on how high you are flying.
Context Anchor
Seen when learning how an Air Route Traffic Control Center organizes its airspace and why pilots are sometimes changed to a different Center frequency.
Derivation
Sector comes from a Latin word meaning “to cut.” In aviation, a sector is a cut-out portion of controlled airspace. High and low describe the altitude layer of that portion.
Why Pilots Care
A controller handoff between high and low sectors occurs when a flight climbs or descends through the dividing altitude.
Intuition Check
High and low do not mean better or worse, and they do not describe radio strength. Here they mean altitude layers within Center-controlled airspace.
Example Sentence 1
After leveling off at FL280, the pilot was handed off from the low sector controller to the high sector controller on a new frequency.
Example Sentence 2
High sector controllers typically manage faster jet traffic while low sector controllers handle a mix of slower aircraft below.