Definition
Movements of air in the upward or downward direction, caused by uneven heating of the surface, terrain features, or weather systems. Vertical currents act on an aircraft in flight by lifting it (updrafts) or pushing it down (downdrafts), causing the altitude and vertical speed to change even when pitch and power are held constant.
Plain English
Air that is moving up or down rather than across the ground. When the aircraft flies through it, the air carries the aircraft up or down with it.
Context Anchor
Seen in instrument flying when the altimeter or vertical speed indication changes even though the aircraft attitude and power setting have not changed.
Derivation
From Latin verticalis, meaning 'overhead' or 'upright,' and current, from Latin currere, 'to run' or 'to flow.' So a vertical current is air flowing in the up-and-down direction, as opposed to the horizontal flow we usually call wind.
Why Pilots Care
They require immediate instrument cross-check and small control corrections to maintain assigned altitude or approach path.
Grounding Statement
Imagine the aircraft sitting on an invisible elevator of air; when that elevator moves, the aircraft moves with it.
Intuition Check
Vertical currents are not electrical currents or water currents. In this aviation use, they are movements of air upward or downward.
Example Sentence 1
While cruising over sun-heated terrain, the pilot noticed the altimeter creeping upward and recognized the climb as the result of a vertical current rather than a pitch change.
Example Sentence 2
Strong vertical currents near the thunderstorm forced constant adjustments to maintain the desired descent rate.