Insights

Dispel the misconceptions

The rectangular course ("Insights: Rectangular Course," January 2006 AOPA Flight Training) teaches students how to compensate for wind while planning and maintaining a linear ground track. When the rectangular course is mastered, students are advanced to S-turns, which are a series of curved ground tracks that lie on both sides of a road as the illustration shows. Students are now required to compensate for wind while maintaining that track.

Some instructors tell students to pick out a ground track that will yield equal radius turns on both sides of the road. Yes, equal radius turns are the apparent objective, and to do that you must adjust bank angle as ground speed changes so that the airplane's lateral axis (the one aligned with the wingspan) is parallel to the road when you cross it. Parallel mandates two conditions: The airplane must be perpendicular to the road at the crossing, and it must be rolling through a wings-level attitude as the airplane transitions from a left bank to a right bank or vice versa.

Like most ground reference maneuvers, the S-turn across a road is begun by flying downwind perpendicular to the road at maximum groundspeed so that the first turn, a medium-bank turn, will be the steepest bank of the maneuver. Bank angle during ground reference maneuvers is a function of groundspeed--higher groundspeed, steeper bank angle, and vice versa. It's unwise to make steep bank turns at low altitude; ground reference maneuvers are flown at 600 to 1,000 feet agl.

When the wing is directly over the road, start the initial, medium-bank turn in the desired direction. Do not start that turn before you reach the road or delay it until you have flown past the road; it must occur when the wing is directly over the road.

To achieve the apparent objective, two primary objectives must occur: First, maintain the initial bank angle until you are no longer moving away from the road. That does not mean that the airplane's longitudinal axis is parallel to the road, it means that your displacement from the road is no longer increasing. That movement, indicated by the double-headed arrows abeam points A and D in the illustration, is easy to determine. Second, when you reverse the direction of turn at the road crossing, the bank angle after you execute the reversal at point C must be exactly the same as the bank angle that existed at point B when you started the reversal. (Never use instrument reference to ensure equal bank angles. This is a visual maneuver.)

When maximum displacement from the road occurs, the airplane will be pointed into the wind as shown at points A and D. At point A, it will be quite obvious that you must reduce bank angle in order to be perpendicular to the road at the crossing. At point D, it will be quite obvious that you must increase bank angle.

I cannot overemphasize the importance of understanding and using these primary objectives. Like so many elements of flying, the apparent objective is seldom the primary objective for executing a maneuver, and this is true for both visual and instrument flying. When the primary objectives are achieved, the apparent objective will occur automatically, and learning will be enhanced.

To master these concepts, you must fly S-turns across a road when wind is present. To do so on a calm day has little, if any, training benefit.

Ralph Butcher, a retired United Airlines captain, is the chief flight instructor at a California flight school. He has been flying since 1959 and has 25,000 hours in fixed- and rotary-wing aircraft. Visit his Web site.