Definition
The minimum vertical separation of 1,000 feet that must exist between an aircraft's altitude and the highest obstacle within a defined area of an instrument approach procedure, applied in non-mountainous terrain during the initial and intermediate segments of the approach.
Plain English
On an instrument approach, the published altitudes are set so the aircraft stays at least 1,000 feet above the tallest obstacle in the protected area around the route, in flat or rolling terrain.
Context Anchor
Seen on instrument approach chart plan views when charted altitudes or protected areas are described in relation to terrain and obstacles.
Derivation
Clearance comes from clear, meaning free from obstruction. In this term, it means a vertical safety margin above obstacles, not permission from air traffic control.
Why Pilots Care
It supplies the required safety margin from terrain and obstacles when flying solely by instruments.
Intuition Check
Do not read clearance here as an ATC authorization. It means physical space between the aircraft’s protected altitude and obstacles below.
Example Sentence 1
In non-mountainous terrain, the initial approach segment is built with a 1,000-foot obstacle clearance above the highest obstruction in the protected area.
Example Sentence 2
Pilots can confirm the 1000-foot obstacle clearance is available before descending on the published track.