A pilot is flying VFR and notes that the surface visibility is 3 statute miles, but the flight visibility appears to be 5 statute miles. If a METAR reports 'BR' (Mist), what is the most likely reason for this discrepancy?
- AThe METAR is reporting RVR (Runway Visual Range) instead of surface visibility.
- BThe 'BR' (Mist) is primarily affecting visibility at the surface, while the air aloft is clearer.
- CThe PIREP was inaccurate due to an optical illusion.
- DThe pilot is experiencing a 'whiteout' condition, exaggerating visibility.
Show answer & explanationAnswer & explanation
Correct answer: B. The 'BR' (Mist) is primarily affecting visibility at the surface, while the air aloft is clearer.
'BR' (Mist) indicates water droplets suspended in the air, reducing visibility to between 5/8 SM and less than 7 SM. Mist often forms in a stable air mass near the surface and can be denser at lower altitudes. It's common for ground-based obscurations like mist or fog to significantly reduce surface visibility while conditions improve rapidly above the lowest layer, leading to better flight visibility at the pilot's altitude.
Why the other options are wrong
- A. METARs report surface visibility unless explicitly stating RVR, which is distinct and typically only for runways. The question states 'surface visibility is 3 SM', which is a reported surface visibility, not RVR.
- C. While optical illusions exist, a consistent discrepancy between surface and flight visibility with reported mist suggests a physical atmospheric phenomenon, not just an illusion.
- D. A whiteout typically reduces, not exaggerates, visibility, making it difficult to discern horizons or features, and usually occurs in snow-covered areas under overcast skies.
Surface vs. Flight Visibility
Surface visibility is reported from the ground, while flight visibility is the average forward horizontal distance seen from the cockpit.
- Can differ significantly, especially with ground-based obscurations.
- Pilots must be aware of both for safe operations.
- Density of obscuring phenomena often varies with altitude.
Memory trick: Ground's got its own view, higher up, the world's new.