WHAT'S THE CEILING?
When it comes time for you to fly solo, your instructor will note limiting weather conditions for your flights in your logbook. One limit likely will be the lowest ceiling under which you are permitted to solo. Another may be a minimum visibility value. [See the Jan. 27, 2006, Training Tip "Solo Limitations."]
Not all cloud cover represents a ceiling. It depends on how much of the sky is visible. The definitions used to describe sky cover carry inferences as to whether a ceiling exists. "A ceiling, for aviation purposes, is the lowest layer of clouds reported as being broken or overcast, or the vertical visibility into an obscuration like fog or haze. Clouds are reported as broken when five-eighths to seven-eighths of the sky is covered with clouds. Overcast means the entire sky is covered with clouds," explains chapter 10, page 17 of the Pilot's Handbook of Aeronautical Knowledge.
You'll find current sky conditions in aviation routine weather reports (METARs) and many automated observations. Sky cover reported as less than broken (few clouds, or scattered layers) does not constitute a ceiling. See the table of contractions on chapter 11, page 6 of the handbook for sky cover, represented in eighths (octas) of the sky from horizon to horizon, for each description.
Why octas? "Students frequently ask why sky cover and obscurations are reported in octas rather than tenths. The four cardinal points of the compass (N, E, W, S) and the four intercardinal points (NE, NW, SE, SW) divide the compass into eight sectors. Cloud cover and obscurations are easy to evaluate if you observe the conditions that exist in each of the eight sectors and base your report on how many sectors that condition occupies. Sky cover is also an element in pilot reports (pireps).
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