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Old 13th Feb 2009, 02:49
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Mansfield
 
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The presence of a vertical visibility observation would indicate an obscuration, and the lack of a ceiling. But ceiling isn't controlling, so the RVR would still be the critical factor. While vertical visibility is an estimate based on looking up into nothing, RVR is a measure of seeing conditions with respect to all of the visual aids, particularly runway lighting. Quote from the FAA Air Carrier Inspector's Handbook:
RVR is an instrumentally-derived value that reflects an artificially created seeing condition on or near the portion of the runway associated with the RVR report. This artificially created seeing-condition is achieved by using high intensity runway edge, TDZ, and centerline lights.
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