Sideslip. 1. To slide sideways and downward along the lateral axis with wings sharply banked. 2. In a turn, a sidewise movement toward the inside of a turn. A skid is a slide sideways away from the center of the turn.

Solo. Flying alone.

Sonic. Pertaining to speed of sound.

Sonic barrier, or sound barrier. Large increase in drag when approaching the speed of sound.

Space platform or station. A large habitable satellite for scientific and military uses.

Span. The dimension of an airfoil from tip to tip.

Spar. The principal longitudinal member in a wing or other airfoil.

Spin. A maneuver, controlled or uncontrolled, in which an airplane dives and spirals at the same time.

Stability. Ability of an aircraft to return to level flight.

Stabilizer. An airfoil which keeps an aircraft steady in flight; includes horizontal member of the tail assembly.

Stall. A condition which occurs when an airplane flies at insufficient airspeed and with the nose too high, creating an excessive angle of attack on the wings and resulting in a loss of lift.

Strut. A rigid member that bears compression loads, such as between longerons in a fuselage or in a landing gear.

Subsonic. Less than speed of sound.

Supercharger. A pump or compressor for forcing air into a reciprocating engine for high altitude flights.

Supersonic. Greater than speed of sound.

Sweepback. The backward slant of a wing or other airfoil.