Definition
In an S-turn maneuver, the two equal, opposite semicircular ground tracks the airplane flies on either side of a reference road or line, each beginning and ending as the airplane crosses the reference line with wings level.
Plain English
The two matching half-loops you fly on opposite sides of a road during S-turns. You roll wings level over the road, fly a half-loop on one side, cross the road wings level again, then fly a matching half-loop on the other side.
Context Anchor
Seen in ground reference maneuver practice, especially when learning S-turns across a road or other straight reference line.
Why Pilots Care
The point of S-turns is to fly two half-circles of equal size and shape over the ground, which requires constantly adjusting bank angle to compensate for wind. If the half-circles come out uneven, the student is not yet correcting properly for wind drift.
Grounding Statement
Picture drawing one smooth half of a circle on one side of a road, crossing the road, then drawing the matching half on the other side.
Intuition Check
Do not think of half-circles here as just any two loose curved turns. In S-turns, they are planned ground paths that should match in size on both sides of the reference line.
Example Sentence 1
The instructor reminded the student that both half-circles in the S-turn should be the same size, with the road as the dividing line.
Example Sentence 2
With a crosswind present, the pilot banked steeper on the downwind side of each half-circle to keep the radius constant.