6.s-turns-across-road. S-Turns Across a Road
S-Turns across a road are a ground reference maneuver designed to develop a pilot's ability to compensate for wind drift while flying a precise track over the ground. The objective is to fly two opposite, equal half-circles of equal radius on either side of a straight reference line on the ground, crossing the line each time with the wings level and the airplane's longitudinal axis perpendicular to the line.
The maneuver is performed at a constant altitude, typically between 600 and 1,000 feet AGL, in accordance with the manufacturer's recommendations and 14 CFR Part 91. A long, straight reference line oriented perpendicular to the wind — such as a road, railroad, fence line, or section line — is selected. Before beginning, the pilot must perform clearing turns, note the wind direction and velocity, and select an emergency landing area should engine failure occur.
Entry. The airplane is flown perpendicular to the reference line on a downwind heading. As the airplane crosses directly over the line, the pilot rolls smoothly into the steepest bank of the maneuver. This is necessary because groundspeed is highest on the downwind side, and the airplane will be drifting away from the line most rapidly at this point. A shallow bank at entry is one of the most common errors and produces a half-circle that is too large on the downwind side.
Tracking the half-circles. As the airplane progresses around the first half-circle, it gradually turns from a downwind heading, through a crosswind, to an upwind heading. As the heading changes, groundspeed decreases, and the rate of drift decreases as well. To maintain a constant-radius half-circle, the bank must be progressively shallowed so that the rate of turn matches the changing groundspeed. The steepest bank occurs at the downwind crossing and the shallowest bank occurs just before the upwind crossing.
The airplane should arrive over the reference line with:
- Wings level
- Longitudinal axis perpendicular to the road
- No drift correction applied at the instant of crossing
Immediately upon crossing, the pilot rolls into a bank in the opposite direction, beginning the second half-circle on the other side of the road. Because the airplane is now starting from an upwind heading with low groundspeed, the initial bank must be shallow. As the airplane turns through crosswind toward downwind, groundspeed increases, drift increases, and the bank must be progressively steepened to maintain the constant radius. The steepest bank again occurs just before crossing the line on the downwind side, where the airplane once more passes over the reference perpendicular and wings level.
Bank relationships. A useful rule of thumb:
- Highest groundspeed → steepest bank (downwind crossing or downwind portion)
- Lowest groundspeed → shallowest bank (upwind crossing or upwind portion)
- Bank is constantly changing throughout each half-circle; it is never held constant for more than an instant
Maximum bank in light training airplanes generally does not exceed 45° and is often much less, depending on wind velocity and the radius selected.
Coordination and altitude control. Like all ground reference maneuvers, S-turns are flown at a constant altitude, with smooth, coordinated use of aileron, rudder, elevator, and power. The pilot must divide attention between outside references (the road, the wingtips relative to the road, the horizon) and occasional glances at the altimeter, heading, and engine instruments. Back pressure must be added in the steeper banks to maintain altitude, and slightly relaxed in the shallower portions.
Common errors.
- Failing to establish a steep enough bank at the downwind entry, producing an oversized downwind half-circle
- Establishing too steep a bank when crossing from upwind, producing an undersized upwind half-circle
- Not crossing the reference line wings level and perpendicular
- Failing to compensate for wind by varying bank angle (flying constant-bank turns)
- Poor altitude control, especially climbing in steep banks due to insufficient back pressure
- Uncoordinated use of controls (slipping or skidding turns), particularly dangerous in the steep, low-altitude phase
- Fixating on the road and neglecting traffic scan and altitude
Example. With a wind from the north at 15 knots and a road oriented east-west, the pilot enters southbound (downwind). At the moment of crossing the road, the airplane is rolled into approximately a 30°–40° left bank. As the heading swings through east (crosswind) to north (upwind), the bank is gradually reduced, perhaps to 10°–15°, so the airplane arrives over the road heading north, wings level. A right bank is then established, beginning shallow and steepening as the airplane turns through east back toward south, completing the second half-circle.
Proficiency in S-turns directly builds the wind-correction skills needed in the traffic pattern, where base-to-final and crosswind-to-downwind turns require the same continuous bank adjustments to track a precise ground path.