PLT553: Minimum Sink Speed
What code PLT553 covers, why the FAA tests it, and how to study Minimum Sink Speed before your checkride.
Recall-Minimum sink speed 15
What this means for your checkride
Minimum sink speed is the airspeed that produces the least altitude loss over a given time, and on the polar it sits at the peak of the sink-rate curve, slower than best glide speed. In the handbook example, a minimum sink of 1.9 knots occurs at 40 knots, while the best L/D speed of 50 knots produces a higher sink rate. Because minimum sink lies close to the stall, it is the speed used to maximize climb while circling in a thermal, though it leaves less margin above stall speed. Sink rate increases between minimum sink speed and the stall at the left end of the polar.
Minimum sink speed is the speed used to stay aloft and climb in lift, so pilots must distinguish it from best glide.
Minimum sink is not the speed for covering the most distance. That is best glide speed, which is faster and used when gliding toward a goal.
Where to study it
A code on your test report is an area of deficiency. An authorized instructor must review it with you and endorse that review before you take the practical test, and the examiner may revisit it during the oral. Study it until you can explain it out loud, not just recognize the answer.