For pilots flying under Visual Flight Rules (VFR), the "ceiling" is a critical safety threshold defined as the height above the earth's surface of the lowest layer of clouds reported as broken or overcast. In controlled airspace (Class B, C, D, or E) that extends to the surface around an airport, the standard minimum ceiling for VFR operations is 1,000 feet. If the ceiling drops below this height, the airport is considered to be under "Instrument Meteorological Conditions" (IMC), and VFR pilots cannot take off or land without a "Special VFR" clearance. Once in the air, VFR pilots must also maintain specific distances from clouds—typically 500 feet below, 1,000 feet above, and 2,000 feet horizontally in most controlled airspace below 10,000 feet. These rules are designed to ensure "see and avoid" capability, providing enough reaction time to steer clear of other aircraft popping out of cloud layers at high speeds.