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Midair collisions are avoided mainly by Visual Flight Rules (VFR) and Instrument Flight Rules (IFR). Visual flight rules apply when the visibility conditions are good. Under VFR, pilots avoid air collisions by seeing other aircraft and avoiding them. VFR also has pilots fly at different altitudes based on what direction they’re heading. IFR applies when aircraft are flying in “class A” airspace, which is the airspace over the US from 18,000-60,000 ft., or in poor visibility conditions. Under IFR pilots avoid collisions based on directions from Air Traffic Control.