Definition
The actual line along which gravity pulls the aircraft and its occupants toward the center of the Earth, perpendicular to the Earth's surface. In straight-and-level, unaccelerated flight, this direction aligns with the pilot's perceived 'down.' During turns, accelerations, or climbs and descents, inertial forces combine with gravity to produce a different felt direction (the resultant force), which can mislead the pilot's sense of true vertical.
Plain English
The real way that gravity pulls you straight down toward the Earth. When the airplane is turning or speeding up, your body feels pulled in a different direction, but actual gravity is still pointing straight down to the ground.
Context Anchor
Seen in discussions of instrument flying and body-sense illusions, where a pilot’s sense of up, down, or turning may not match what the aircraft is actually doing.
Derivation
Gravity comes from the Latin word gravitas, meaning heaviness or weight. That helps here because this term is about the real pull that gives weight its direction: downward toward Earth.
Why Pilots Care
During maneuvers the body senses a false vertical, so pilots must ignore physical feelings and trust instruments to avoid spatial disorientation.
Grounding Statement
Imagine standing in an elevator that suddenly accelerates upward -- you feel heavier, as if gravity got stronger. Gravity hasn't changed; the acceleration just added to it. In an aircraft, the same effect makes the pilot's felt 'down' point somewhere other than true down.
Intuition Check
Do not assume “true direction of gravity” means the direction that feels most natural to your body. In this context, it means the actual pull of gravity, even when motion makes your body feel something else.
Example Sentence 1
In a steady, coordinated turn, the pilot's sense of 'down' shifts toward the floor of the aircraft, even though the true direction of gravity still points toward the Earth.
Example Sentence 2
When the airplane enters a turn the pilot feels a tilted vertical, yet the true direction of gravity remains straight toward the Earth center.