Definition
The protected airspace evaluated around an en route fix where a course change occurs, used to determine the Minimum Turning Altitude (MTA) needed to guarantee obstacle clearance throughout the turn. It accounts for the aircraft's turn radius, bank angle, ground speed, and wind, and extends outward from the fix to ensure terrain and obstacles inside and outside the turn remain clear by the required margin.
Plain English
It is the chunk of sky around a turning point on an airway that has been checked for terrain and obstacles, so planners can set a safe minimum altitude for making the turn there.
Context Anchor
Seen in instrument procedure and minimum turning altitude discussions, especially when a turn at a fix needs extra altitude for obstacle clearance.
Derivation
"En route" is from French, meaning "on the way," and refers to the cruise phase between departure and arrival. "Turning area" is literal: the airspace evaluated around the turn. Together it describes the on-airway space examined for clearance during a course change.
Why Pilots Care
It gives the pilot a known safe altitude to begin a turn without risking terrain or obstacle conflict during the maneuver.
Grounding Statement
Picture the aircraft turning through a wide curved path in the sky; the protected area is the space around that curved path that must stay safely clear of obstacles below.
Intuition Check
Do not read “turning area” as a painted or physical area on the ground. Here it means a designed block of protected airspace around the aircraft’s expected turn.
Example Sentence 1
Because the en route obstacle clearance turning area at that fix included rising terrain, the chart published an MTA 1,800 feet above the MEA.
Example Sentence 2
The en route obstacle clearance turning area allowed the aircraft to turn safely from one airway to the next without descending below the calculated floor.