Definition
A visibility hazard occurring over snow-covered terrain in which a uniformly overcast sky combined with diffuse, reflected light from the snow eliminates the visible horizon, shadows, and surface contrast within a particular sector of the pilot's view. The pilot can still see clearly in other directions, but in the affected sector, the ground and sky blend into a single featureless white field, making it impossible to judge altitude, distance, or surface slope.
Plain English
A condition where, in one direction of the view, snow on the ground and clouds overhead blend together so completely that the pilot can no longer tell where the ground ends and the sky begins. The rest of the view may still look normal.
Context Anchor
Encountered during operations over snow-covered or ice-covered terrain, especially during approach, landing, low-level flight, or taxi in flat light.
Derivation
"Sector" comes from the Latin sectus, meaning "cut" — here it means a portion or slice of the pilot's surrounding view. "Whiteout" describes the visual effect of everything turning white. Together, the term means a whiteout that affects only part of the view rather than the entire surroundings.
Why Pilots Care
Can trigger spatial disorientation if the obscured sector includes the primary horizon reference.
Grounding Statement
Imagine looking out one side of the cockpit and seeing snow, terrain, and a clear horizon — then turning your head and seeing nothing but a smooth wall of white in every direction within that view.
Intuition Check
Do not assume a sector whiteout means everything outside the aircraft has gone white. It means one direction or portion of the view has lost contrast enough to become unreliable.
Example Sentence 1
While flying over the snowfield under an overcast sky, the pilot lost the horizon ahead and recognized a sector whiteout, so she turned toward terrain features still visible to the south.
Example Sentence 2
After climbing above the blowing snow layer, the crew left the sector whiteout behind and regained full visual references.