Phugoid

400px|thumb|right|A diagrammatic representation of a fixed-wing airplane in phugoid

In aviation, a phugoid or fugoid () is an aircraft motion in which the vehicle pitches up and climbs, and then pitches down and descends, accompanied by speeding up and slowing down as it goes "downhill" and "uphill". This is one of the basic flight dynamics modes of an aircraft (others include short period, roll subsidence, dutch roll, and spiral divergence).