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Which one of the following below may reduce the visibility for an aircraft performing a low level VFR flight on a day with clear sky?
  • A
    Climbing to a higher altitude.
  • B
    Flying downwind of factories producing smoke.
  • C
    Flying with the sun behind the aircraft.
  • D
    Sun is high in the sky.

The pilots flying VFR must check if the sky is obscured, meaning that something is totally or partially blocking his/her view of either the sky or the ground.

Obscurations (and their abbreviations) include: mist (BR), fog (FG), smoke (FU), volcanic ash (VA), sand (SA), haze (HZ), spray (PY), and widespread dust (DU).

Smoke may come from factories and forest fires. Even far downwind of smoke, the smoke is often spread out, somewhat uniformly, within the bottom several low levels of the atmosphere. In some cases the smoke is so thick that it is difficult to see the bottom parts of the clouds and can reduce visibility to the point, where it is a hazard to aviation.

Furthermore, visibility may be also reduced, if flying with the sun in front of the aircraft or with the Sun low in the sky.

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