✈️ Aviation Brief — Issue #95
Weekly insights for student pilots and the instructors who train them.
THIS WEEK'S TOPIC
CA.VI.B — S-Turns (Commercial Pilot ACS)
1. ACS STANDARDS SUMMARY
The Commercial Pilot ACS (CA.VI.B) requires the applicant to perform S-turns across a straight ground reference line (such as a road or section line) perpendicular to the wind. The pilot must maintain coordinated flight while varying bank angle to produce constant-radius semicircles on each side of the line, crossing the reference line at 90° with the wings level. The maneuver must be flown at a constant altitude (±100 feet) and airspeed (±10 knots), with proper wind-drift correction applied throughout. The examiner expects smooth, timely bank changes that demonstrate understanding of how groundspeed affects turn radius.
2. THREE COMMON STUDENT MISTAKES
- Failing to vary bank angle with the wind: students often hold a constant bank, producing a tighter turn upwind and a wider turn downwind instead of matching the semicircles.
- Poor timing of roll-in and roll-out: rolling into the turn too early or too late causes the airplane to cross the reference line at an angle other than 90° or at an unequal distance from the start of the previous turn.
- Neglecting altitude and airspeed while fixating outside: students chase the reference line visually and allow the airplane to climb or descend, especially when correcting for strong winds.
3. CFI PRO TIP
Have the student pick two points on the reference line that represent the widest part of each semicircle and verbalize “start roll-in here, reach maximum bank at the farthest point, begin rollout here.” This forces them to think in terms of the full circle geometry rather than reacting only to the line, producing smoother, more symmetrical turns after just two or three practice runs.
4. SAFETY SPOTLIGHT
Low-altitude ground-reference maneuvers remain a leading contributor to loss-of-control accidents during training. NTSB accident data shows multiple cases in which students practicing S-turns or turns around a point entered stall/spin scenarios after letting airspeed decay while correcting for unexpected wind shifts close to the ground. Maintaining the ACS altitude and airspeed tolerances is not just a checkride requirement—it keeps the airplane well above stall speed while attention is divided between the ground reference and cockpit instruments.
5. DID YOU KNOW
S-turns were originally developed during World War I as a way for artillery spotters to maintain a steady track over a road or railroad while compensating for wind without the observer losing sight of the target.
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