The Federal Aviation Administration (FAA) shares the Environmental Protection Agency's (EPA) concerns about lead emissions from small aircraft. Owners and operators of more than 200,000 piston-engine aircraft operating in the United States rely on aviation gasoline (avgas) to power their aircraft.
Symmetry (noun). a due proportion of the several parts of a body to each other; adaptation of the form or dimensions of the several parts of a thing to each other; the union and conformity of the members of a work to the whole. Symmetry (noun).
Symmetry is when elements are arranged in the same way on both sides of an axis. Perfect symmetry is when elements are mirrored over the axis and exactly the same on both sides. Symmetry adds balance to a design. When elements are the same on both sides of an axis, the design feels harmonious. If we design a street with five houses on one side and five on the other, walking down the street would feel comfortable because the arrangement of homes is balanced.