The Improbable Turn | GroundSchool.com

The Improbable Turn

impossible turnI Saw It on the Internet

The long-maligned "impossible turn" has recently enjoyed a comeback. The controversial topic is suddenly front-and-center on social media, and everyone is an expert. In the process, however, a new danger has appeared: misinformation disguised as pilot wisdom. The internet gives a big megaphone to everyone and there is no effective filter to separate the good advice from the bad. 

YouTube videos portray staged executions of the turnback maneuver (the real name), making it look easy in a specific set of conditions. But they also fail to indicate what the collection of mitigating factors are. And there are a lot of them. The majority of people are unware that these factors even exist. 

The common wisdom is that it's based on some particular altitude. If you are x-number of feet AGL, you can do it. If you're lower than that, you cannot. This piece of information is the first link in a chain that frequently ends in the Nall reports.

 

the impossible turn

 

The turnback maneuver can be impossible, improbable, or possible. It all depends on that variety of factors. Under the right circumstances it may be your best option. But proper execution of the turnback maneuver is frequently mistated. Advice is often oversimplified to the point of being dangerous.

The Turnback Altitude

This idea that one altitude fits all is one of the most pervasive - and dangerous - pieces of misinformation. Whether you have heard 700 feet, or 1000 feet, or any other number, please disregard it. There is no one altitude that works for everyone. 

There is an altitude that I call the decision height (DH) which, under certain conditions, may allow the option to turn back to the field in an emergency. The problem is that the DH must be adjusted for every flight based on factors including wind, runway length, climb gradient, and density altitude. Consider this example:

You have determined that 700 feet is a safe altitude for you to turn back to the runway. You have practiced this on a 5000 foot runway, and easily made it back onto the pavement just past the numbers. Now, what if the conditions were exactly the same, except that the runway length was only 3000 feet? The correct answer is: you wouldn't make it. It really is that simple. Runway length is a huge factor in successfully executing a turnback. Yet, it is rarely mentioned when the turnback discussion comes up. Ignore that one factor and you won't get the result you expect.

Another example: As before, you have determined that 700 feet is your safe turnback altitude (your DH). Instead of using the climb gradient that you tested earlier, your climb is considerably more shallow. At 700 feet, you successfully get the airplane turned around and pointed toward the airport. But because of your shallow climb, you are considerably further from the runway. Will you make it? Probably not. 

These are just two factors that are consistently ignored. Even by themselves, they illustrate that altitude (DH) alone is not the deciding factor in this manuever.

Bank Angle

In the early 1980s, the Dept. of the Navy did concentrated research on the turnback maneuver. They determined that 45° of bank was optimal. It provided the best mix of altitude loss and distance from the extended centerline. But it also noted something very important: at 30° of bank, the altitude loss was essentially the same. A bank of 30° does take you further from the centerline, but not much. 

Performing a precise (in terms of airspeed and bank angle) steep spiral is not as simple as it sounds. It's not terribly difficult, especially if you are willing to settle for sloppy performance. But it does need to be practiced. It is demonstrably easier to perform at 30° than at 45°. Remember, we're expecting a high degree of precsion in a high stress situation.

And there's another thing about 45° - stall speed increases in proportion to the square root of the load factor. At 45 degrees of bank, load factor increases by 40%, and stall speed in most light singles increases by roughly 10 knots. The turnback maneuver should be executed at best glide speed (assume level flight). When performing this at 45° the difference between stall speed and glide speed is substantially smaller. For these reasons, my suggestion is to plan and practice this maneuver at 30°. Not 25, not 35. Practice and become proficient at precisely 30 degrees of bank. 

The Takeoff Profile

Roughly 25% of fatal general aviation accidents occur during the first three minutes of flight. On a day VFR departure, this is possibly the most dangerous period of the entire flight. Reduce your risk by recognizing the Four Phases of the takeoff profile. Each has different risks and different mitigations. And brief before every takeoff. At the very least, decide which way you will turn if turning is an option (based on wind and runway configuration).

Takeoff Profile

White - Takeoff Roll - Low Risk

Recognize any anomaly including loss of directional control and promptly stop on available runway.

Yellow - Takeoff - Moderate Risk

Recognize the problem quickly and pitch down. Reduce the angle of attack. Transition to a landing configuration and land on available runway (or clear overrun).

Red - Initial Climbout - High Risk

This is where the impossible turn lives. Minimize your time in this phase. Get high fast. In an emergency, pick your best spot in a shallow pie slice in front of you and fly it all the way to the ground. Maintain aircraft control for as long as possible. Don't give up.

Yellow - Departure Climb - Moderate Risk

This phase starts at the point where you reach DH. It is where the highest risk phase becomes a moderate risk. You are at a high enough altitude where you have options available, beyond simply landing straight ahead. 

Know where you are at every second during your takeoff and departure climb. Be situationally aware and recognize your options at every single point. Practice your options until you have reached proficiency. Brief before every takeoff to improve your recognition and response times. And be very careful about advice you see on social media. Everyone has a big megaphone. Not everyone has the knowledge necessary to deliver a safe message.

Practice  ●  Proficiency
Recognition  ●  Response
Brief Before Every Takeoff

 

 



Russ Still

About the Author

Russ Still is a career flight instructor and ATP. He has written numerous articles for technology and aviation publications and authored “The Unbroken Chain” in 2001 (ISBN-10: 189652284X). Russ is an 8-time Master CFI and founded the Gold Seal Aviation Training Network in 2003. He holds a Bachelor of Science in Computer Science from the University of Florida.