Readback: August 2017

In April Killer Quiz, The Prof and the Pilot, I dont think that the answer to the last question is correct. With tailwind, one should reduce the airspeed below best glide speed, which in turn reduces the sink rate. Gliders pilots are very familiar with these concepts.Unfortunately, Cessna doesnt publish sink rates at various speeds to compute that accurately, so we are left to back-of-the-envelope calculations. We know that at best-glide speed (65 knots.

Editorial Staff

Wednesday, July 05, 2017 at 12:00 AM ET

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Key Takeaways:

An exchange about optimal descent speed with a tailwind highlights the theoretical benefit of reducing airspeed below best glide for a lower sink rate, but notes its impracticality for piston singles due to complexity and small margin of error.
The decline in general aviation is attributed more to skyrocketing liability costs (due to lawsuits) that inflate aircraft prices and overly restrictive airport security measures (fences, interrogations) than to FAA regulations or fuel costs.
Autopilot restrictions on some ILS approaches, but not RNAV, are due to ILS radio beams being susceptible to interference from terrain/obstacles, causing erratic signals that autopilots react to more abruptly than human pilots.

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Higher Math

In April Killer Quiz, “The Prof and the Pilot,” I don’t think that the answer to the last question is correct. With tailwind, one should reduce the airspeed below best glide speed, which in turn reduces the sink rate. Gliders pilots are very familiar with these concepts.
Unfortunately, Cessna doesn’t publish sink rates at various speeds to compute that accurately, so we are left to back‑of‑the‑envelope calculations. We know that at best‑glide speed (65 knots), sink rate is 730 fpm and this requires 73 knots tailwind to reach the threshold. Assuming that sink rate is 600 fpm at 50 knots, which seems realistic, flying at 50 knots would need only 63 knots tailwind.
I love your quizzes. I learn something from each one.

Thomas Daniel
Portola Valley, CA