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 also has an aesthetic meaning, although this is harder to define; artistic symmetry is beauty found in a pleasing and regular form. There are many kinds of symmetries, from the left-right symmetry of a face (left), to the five-fold symmetry of a starfish (center), to the complete symmetry of a circle (right). These sorts of symmetries are also seen in physics theories, leading some physicists to describe the equations as beautiful.