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The Aerodynamics Behind Flying Emergency Descents

Do you remember the last time you practiced flying an emergency descent? Outside of training, you may never have to fly one as a pilot. Here's what you should know about some of the aerodynamics that makes this maneuver possible...

Each type of airplane has different procedures and configurations for emergency descents. In this article, we'll focus on the piston, single-engine airplanes almost everyone completes flight training in.

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But First, What Exactly Is An Emergency Descent?

Simply put, an emergency descent is a maneuver for descending as rapidly as possible to a lower altitude, usually for a landing. Whether you're flying a Boeing 777 or Piper Warrior, every pilot trains on how to fly emergency descents. Outside of training, they're triggered by worst-case, often life-threatening emergencies.

There are dozens of reasons why an emergency descent might be appropriate, including uncontrollable fires, rapid cabin depressurization, or anything else requiring an immediate need for lower altitude.

Reducing Lift

According to the FAA's Airplane Flying Handbook, "when initiating the descent, a bank of approximately 30 to 45 degrees should be established to maintain positive load factors (G forces) on the airplane."

Another reason for this bank angle is to reduce your vertical component of lift, helping the rapid descent. If you roll into a turn using only ailerons (without applying back-pressure), your vertical lift decreases and your horizontal lift increases. The airplane tends to descend during aileron-only turns.

Maximizing Drag

While all emergency descent training should follow manufacturer recommended configurations and airspeeds, you'll fly an emergency descent with a "dirty" configuration in most light, single-engine airplanes. If equipped with a constant speed propeller, the prop "should be placed in the low pitch (or high rpm) position. This allows the propeller to act as an aerodynamic brake to help prevent an excessive airspeed buildup during the descent" (FAA).

The landing gear and flaps should be extended as recommended by individual manufacturers; both will help increase drag. The goal is to fly the most rapid descent possible without excessive airspeed while also taking into account aircraft speed limitations.

Controlling Speed

A critical part of flying safe emergency descents is speed management. You should never exceed Vne, or the structural never-exceed speed. When configuring the airplane for additional drag during descent, take into account maximum landing gear extension speed (Vle) and maximum flaps extended speed (Vfe).

Putting Out Fires (Literally...)

Emergency descents are often used to blow out the flames of a fire. High airspeed descents are best for this, however, the possible weakening of the airplane's structure is a major concern. This is where your decision making as a pilot will play an important role. You must determine (or make an educated guess) about where the fire is and how much structural damage may have occurred. Slow the airplane down accordingly.

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Don't forget about Va, or maneuvering speed, either. If descending through turbulent air, you should slow to Va or slower to ensure you don't damage your airplane if full control deflections become necessary.

Choose Your Recovery Altitude Wisely

An emergency descent is usually a result of a sudden, uncontrollable event. If you find yourself flying one, you may not have time at first to fully plan out a recovery altitude. Once you've configured the airplane, followed the checklist, and are flying the descent, begin to plan how you'll level off.

You should initiate recovery at an altitude high enough to ensure a safe recovery back to level flight, or a precautionary landing.

_Night Flier_

If you're practicing emergency descents during training, keep an eye on your engine temp. You don't want to excessively cool your piston engine's cylinders during a prolonged idle descent. Once the descent is stabilized during training, consider recovering, and bring your power up slowly.

When was the last time you practiced flying emergency descents? Tell us in the comments below.

Swayne Martin

Swayne is an editor at Boldmethod, certified flight instructor, and an Embraer 145 First Officer for a regional airline. He graduated as an aviation major from the University of North Dakota in 2018, holds a PIC Type Rating for Cessna Citation Jets (CE-525), and is a former pilot for Mokulele Airlines. He's the author of articles, quizzes and lists on Boldmethod every week. You can reach Swayne at swayne@boldmethod.com, and follow his flying adventures on his YouTube Channel.

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