Visibility

Visibility is the greatest horizontal distance at which prominent objects can be seen and identified by the unaided eye. In aviation, it determines whether visual or instrument flight rules apply and whether an approach can be completed.

• Reported in METAR in meters (ICAO) or statute miles (USA)
• Prevailing visibility: the greatest distance visible over at least half the horizon
• RVR (Runway Visual Range): measured by transmissometers along the runway
• Minimum visibility values are defined for each approach category (CAT I, II, III)
• Flight visibility vs. ground visibility may differ significantly