Definition
Pie-shaped divisions of the area surrounding a navigation facility on an instrument approach chart, each labeled with its own minimum safe altitude. They provide obstacle clearance for an aircraft within 25 nautical miles (or 30 NM for some approach charts) of the facility, with each sector reflecting the highest obstacle in that slice of airspace.
Plain English
On an approach chart, the area around a navigation station is split into pie slices, and each slice has its own lowest safe altitude. Different slices can have different minimum altitudes because the terrain or obstacles are different in each direction.
Context Anchor
Seen on IFR low altitude en route charts when choosing or changing the ATC frequency for a route segment.
Derivation
Sector comes from a Latin word meaning “to cut.” In aviation, airspace is cut into manageable pieces so different controllers can handle different areas. Altitude comes from a Latin word meaning “height,” which fits the idea that these sectors apply to aircraft operating in a lower height band.
Why Pilots Care
Knowing you are operating inside a low altitude sector helps anticipate controller handoffs and frequency changes.
Intuition Check
Low altitude sectors are not simply “low areas near the ground.” They are controller airspace areas used for lower IFR en route operations. They also are not minimum safe altitude areas; they are mainly about ATC responsibility and communication.
Example Sentence 1
After the missed approach, the pilot checked the low altitude sector for their position and climbed to the published minimum for that sector.
Example Sentence 2
Departures from this airport remain in low altitude sectors until reaching 14,000 feet.