Flat light

Flat light is an optical illusion, also called sector or partial whiteout: under overcast skies, a pilot loses depth of field and contrast in vision (AIR 2.12.8). Less severe than whiteout (see aeronautics/whiteout).

• Where: primarily snow-covered areas; also dust, sand, mud flats, glassy water. Occurs worldwide.
• Terrain: features can be completely obscured, so distances and closure rates cannot be judged.
• Attitude: reflected light can give the illusion of climbing or descending in level flight.
• Safe operation possible with good judgment, proper training and planning.

Trap: dismissing flat light as ordinary haze; it strikes under overcast, and the danger is misjudged distance, closure rate or a false climb/descent.

Practice