Mastering the Glide

Learning to fly means mastering four fundamentals: climbs, descents, turns, and straight-and-level flight. Today, I’ll discuss one type of descent: the glide. Gliding is an underrated skill that too few pilots understand or practice.

Regularly practicing gliding descents teaches pilots one of an airplane’s important limits and builds confidence. Knowing how far an airplane can glide — and how to glide properly — makes an engine failure at altitude less concerning, provided you have planned your route and altitude appropriately.

First, know your airplane’s glide ratio. Calculate it by dividing the horizontal distance traveled in one minute by the altitude lost during that minute. For example, a Cessna 172 flown at its optimum glide speed of 65 knots travels 6,582 feet per minute. With a descent rate of 725 fpm, 6,582 ÷ 725 yields a glide ratio of 9:1. The airplane travels forward nine times farther than it descends.

With an engine failure at one nautical mile — approximately 6,080 feet — above ground level, a 172 can glide about 9 nautical miles in any direction in no wind. At twice that altitude, 12,160 feet, the glide distance doubles to 18 nautical miles, and the potential landing area quadruples. Altitude truly is money in the bank.

It is important to fly the best glide speed accurately. It is easier to do so if the airplane is trimmed for best glide speed. HINT: Most light aircraft are in trim for best glide with full nose-up trim. 

Poorly trained pilots might try to “stretch” a glide by raising the nose to reduce the sink rate. That places the airplane closer to a stall and reduces airspeed. Slower airspeed means more time to reach the landing site — and more time to lose altitude — so glide performance suffers. In still air, any deviation from best-glide speed reduces glide distance. If best-glide airspeed will not get you to the runway, no airspeed adjustment will. If power is available, add it; otherwise, choose a closer landing site.

Use this glide-stretching technique only as an absolute last resort — and never while there is any reasonable possibility that the engine can be restarted. Do not attempt to stop the propeller until you have concluded that the engine is truly inoperative, restart attempts are no longer practical or appropriate, and you have sufficient altitude and a suitable landing outcome in mind.

Only then, with the throttle closed and at a safe altitude, raise the nose enough to slow the airplane until the propeller stops. Cessna testing found that stopping a Cessna 172’s propeller improved glide ratio by approximately 20 percent. Once the propeller has stopped, lower the nose promptly and accelerate back to the published best-glide speed.

Regular power-off approaches help students visualize the airplane’s glide path and master gliding while power is still available — preparing them for the unlikely day when power is lost. With practice, pilots can predict where the airplane will touch down, on or off the runway.

Wind also affects glide performance. A tailwind extends glide range; a headwind reduces it. To maximize a tailwind’s benefit, glide slightly slower than normal to give the wind more time to help. Into a headwind, glide slightly faster. Although the descent rate increases, the added airspeed maximizes forward progress. As a rule of thumb, reduce airspeed by 4, 6, or 8 knots for tailwinds of 10, 20, or 30 knots, respectively. For a headwind, increase airspeed by 50 percent of the headwind component.

What goes up must come down, but how an airplane comes down matters greatly to those aboard. Without engine power, there are only two choices: accurately and with a plan, or sloppily and with a surprise ending.