Definition
The vertical distance between the lowest point of a helicopter's skids or wheels and the highest point (the crest) of an obstacle directly beneath it as the helicopter passes over. Used in confined-area and pinnacle operations to ensure safe terrain and obstacle separation during approach, hover, and departure.
Plain English
How much room you have between the bottom of the helicopter and the top of whatever you are flying over, like a tree, ridge, or fence.
Context Anchor
Used in mountain flying, route planning, and any discussion of crossing ridges or passes safely.
Derivation
Crest comes from the Latin crista, meaning 'tuft' or 'top of something,' later used to mean the highest point of a ridge, hill, or wave. Clearance here means 'space between things.' Together: the space above the highest point you're flying over.
Why Pilots Care
Maintains safe terrain separation and accounts for downdrafts or performance limits in mountainous areas.
Grounding Statement
When crossing a ridge, crest clearance is the safety space between the airplane and the top of that ridge.
Intuition Check
Clearance here does not mean permission from air traffic control. It means physical space between the aircraft and the terrain crest.
Example Sentence 1
As he crossed the ridge, the pilot maintained adequate crest clearance to keep the skids well above the rocks below.
Example Sentence 2
Before descending into the valley, the instructor checked that crest clearance would remain adequate given the reported winds.