Definition
A defined area on an instrument approach chart, depicted as part of the sectorized minimum safe altitude (MSA) or terminal arrival area (TAA) construct, in which the published altitude provides obstacle clearance but is lower than the highest sector altitude and higher than the final approach segment. It allows aircraft arriving from that direction to descend in a stepped manner toward the final approach course while remaining clear of terrain and obstacles.
Plain English
A pie-slice-shaped piece of the approach chart with its own minimum altitude. It sits between the highest protected altitude and the final approach altitude, giving you a safe step-down level as you get closer to the airport from that direction.
Context Anchor
Seen on instrument approach charts that divide the arrival or approach area into sectors with different minimum altitudes.
Derivation
"Intermediate" comes from Latin intermedius, meaning "in the middle." "Sector" comes from Latin sector, meaning "a cutter" or "a slice" — a pie-slice-shaped portion of an area. Together: a middle-level slice of the protected airspace around an airport.
Why Pilots Care
Following the published altitude in this sector keeps the aircraft clear of obstacles during the approach transition.
Intuition Check
Do not read “intermediate” as vague or approximate. Here it means a specific published middle area of the procedure with a specific altitude limit.
Example Sentence 1
Arriving from the northeast, the pilot identified the intermediate altitude sector on the TAA and descended to the published altitude before continuing inbound.
Example Sentence 2
ATC cleared the flight through the intermediate altitude sector before issuing the final approach fix.