Lesson 6: Visibility
Lesson Content

There are there are two broad classifications of ceiling and visiblity conditions:

  1. Visual Meteorological Conditions (VMC) and the flight rules of VFR (Visual Flight Rules). This is also includes a subdivision refered to as Marginal Visual Flight Rules (MVFR).
  2. Instrument Fligth Rules (IFR), with rules defined by IFR (Instrument Fligth Rules). Ceiling and visibilty is further subdivided into the LIFR (Low Instrument Flight Rules).

ere is some additional information on the standard atmosphere, and some brief notes.

You should already know some basic definitions, such as Latitude, Longitude, Altitude and Gravity.

Below is a brief summary of some of these topics.


VFR and IFR criteria conditions

VFR: ceiling > 3,000 feet AGL (above ground level) and visibility > 5 s.m.

MVFR: ceiling 1,000 to 3,000 feet AGL and/or visibility 3 to 5 s.m.

IFR: ceiling 500 to < 1,000 feet AGL and/or visibility 1 to 3 s.m.

LIF: ceiling < 500 feet AGL and/or visibility < 1 s.m.


RVV: Runway visibility is the visiblity from a particular location along an identified runway.

RVR: Runway visual range is the maximum horizontal distance down a specified instrument runway that a pilot can see and identify standard high intensity lights.

Ceiling: The height above the earth's surface of the lowest layer reported as broken or overcast, or as the vertical visibility into an indefinite ceiling.

Vertical Visibility is the vertical distance that an observer or some remote sensing device can see into a cloud.

Prevailing visibilty is the greatest horizontal distance over which objects or brigth lights can be seen and identified over at least half of the horizon circle. Prevailing visibiliy is taken as the representative visibility at a particular location.

CAVC - eiling and visibility OK - used when there is no significant weather and the visibility exceeds 10 kilometers and either there is no ceiling less than 1,500 meters or no ceiling below the highest ATC sector altitude whicheever is higher.

Some inflight issues to remember:

Heading into the sun greatly reduces your visibility due to the reflection from haze; appart from the glare.

With the sun behind you, even on a haze free day you can have problems as shadows from scattered cloud conditions can obliterate your view of scheduled way-points en route.

Inversions near the ground, which can be associated with high pressure systems, can have low visibility near the ground while skies appear crystal clear above the inversion.

Visibility is very much reduced when flying at night.

Radiation fog is quick to form on a clear day on an autumn or winter evening, and can do so very early on a spring or summer morning. When you see high humidity, it is safest to skip that attractive late afternoon clear sky flight during autumn and winter.

Vertical visibility may enable sight of an airfield from directly overhead, but it my be insufficient to see the airfield on horizontal approach.