The FAA is hot on energy management—here’s why it matters
|
Getting your Trinity Audio player ready...
|
Sharp-eyed readers (or anyone with a moderate case of insomnia) may have noticed a new chapter in the latest edition of the FAA’s Airplane Flying Handbook. This venerable textbook, which has been essential reading for student pilots for decades, doesn’t see too many updates—the laws of physics stay fairly constant—but the new chapter four is definitely worth reading.
A smooth landing is mostly about energy management.
Over 19 pages of text, formulas, and charts, the FAA tackles a hot topic in aviation education, one this book has ignored until now: energy management. It sounds boring, and parts of the new chapter definitely are, but the main concept is critical for safe and smooth flying. What most pilots mean when they say “stick and rudder flying” is really energy management, the process of constantly adjusting your airspeed, altitude, and power to arrive at your intended destination under control.
The basic concept is both simple and profound: every airplane flies because of some combination of potential energy (altitude) and kinetic energy (airspeed). Think of it as two buckets that have varying levels of water. Right after takeoff, both buckets are nearly empty since your altitude and airspeed are both low. If the engine quits, you’ll be landing very soon. In cruise flight, both buckets are fairly full, so your options for an emergency landing are much better—you can use the airspeed above best glide to maintain altitude, then use the altitude above the ground to glide down. Glider pilots, lacking an engine to make their own kinetic energy, have a natural sense of their energy state throughout a flight and are constantly running these types of rough calculations.
It’s important to note, however, that more energy is not always better. A pilot on short final in a Cessna 172 who is both fast (too much kinetic energy) and high (too much potential energy) is setting himself up for a bad landing. All that energy needs to be dissipated before a safe, controlled touchdown can happen. That’s where flaps and slips come into play; if those don’t work it’s time for a go-around. You simply cannot make the airplane land if there’s too much energy—it’s like trying to douse a fire that’s still connected to a full propane tank.
The bucket analogy is easy to visualize, but for more aviation-specific scenarios, consider the following matrix from the FAA:
Green is ideal, red is unsafe, and blue is too high. The bottom left block would be a bad place for an engine failure; the top right would be a bad place to be on short final.
Remember that total energy is not static; it’s constantly changing as the airplane moves through the air and as pilots transfer water from one bucket to the other. For example, you can turn kinetic energy into potential energy, the old “trade airspeed for altitude” trick you may have seen your flight instructor demonstrate. By pulling back on the yoke to climb, you’re pouring water from the kinetic bucket into the potential bucket.
This suggests a critical insight for pilots: control inputs are interrelated. You may have heard the phrase, “pitch for airspeed, power for altitude.” That’s true in a basic sense, but the reality is that pitch and power must be used together, depending on the unique requirements of each situation.
Take the middle left block in the graphic above, during an approach to landing. You are most likely on glidepath and slow; pitch down and you’ll increase your airspeed (fix the low kinetic energy problem) but you’ll decrease your altitude too (taking potential energy from OK to low). Should you pitch for airspeed in this situation?
Yes, but be prepared to add power if you notice the VASI turning red over red. I am a huge advocate of making one change at a time—in this example I would suggest the pilot first fix the airspeed problem and see what happens for a few seconds—but they should have their hand on the throttle in case it’s time to add “power for altitude.”
Low kinetic energy and high potential energy: the answer is probably to trade the latter for the former.
This is the best way to use the concept of energy management: to stay one step ahead of the airplane. By developing a gut feel for your current energy state, you can start to anticipate what control inputs might be required, leading to smoother and easier flights. Don’t worry about exact values or formulas; the point is to understand which parts of a typical flight are low energy vs. high energy, how controls can affect the distribution of energy, and how to react.
Parts of the new Airplane Flying Handbook chapter are far too complicated—indeed, the FAA has managed to make a relatively simple subject look like a physics dissertation at times—but it is still worth reading. This is not some academic subject that’s only helpful during barstool debates with other pilots. As the FAA says, “Mismanagement of mechanical energy (altitude and/or airspeed) is a contributing factor to the three most common types of fatal accidents in aviation: loss of control in-flight (LOC-I), controlled flight into terrain (CFIT), and approach-and-landing accidents.”
Once you’ve read the new chapter, go out and put this theory into practice. Ask your flight instructor to set up scenarios with varying levels of potential and kinetic energy, and then notice how the airplane reacts to changes in pitch or power. You’ll know you’re making progress when you start to react to undesirable changes before the airplane gets too far from that green section in the middle of the chart.
Better energy management might prevent an expensive mistake, but at the very least you may find your next landing is a little smoother.
- Silent Threat: Carbon Monoxide Poisoning Risks for Pilots - November 18, 2024
- Starting flight training later in life: some tips for success - May 31, 2024
- Tough flight instructors are worth it… most of the time - May 25, 2024
about time for this very simple concept…let’s hope folks can keep it simple without adding pseudo-science to disguise when they don’t really understand it or start using equations to quantify!
…another good exercise is to show the limits of trading altitude for airspeed, that you can only gain so much airspeed in a descent before drag chews up some of that energy and you don’t make it all the way back up to your original altitude after reversing the trade. Kind of like that high school physics demo where the ball on a string released from near your nose will not swing back and hit you in the nose.
I just finished re-reading Langewiesche’s Stick and Rudder; does a good job of addressing energy management, albeit without any complicated charts/graphs/formulas. I’m constantly amazed when reading him that the basics/physics haven’t changed over time … :-)
John, absolutely excellent, and well needed article!! The new AFH Chapter 4 has been long needed and quite good, but I agree with you about parts of it being much more complex (thus difficult for some non-engineers to understand) than needed.
Energy management is mentioned in nine places in the Private Airman Certification Standards (under flying stabilized approaches), where your discussion on “pitch for speed, power for altitude” definitely comes into play. As you mentioned, energy management is a relatively easy to understand “concept,” useable without any higher math.
One very minor comment, paragraph 7 about “total energy is not static…transfer from one bucket to another.” It might be more correct by changing “total” to “mechanical” or commenting how total energy includes airspeed & altitude (which can be interchanged) plus finite amount of chemical energy (gallons of fuel which will be added to altitude or airspeed) and airmass energy (drag which will be subtracted from altitude or airspeed).
Again, great article. Thanks.
John, Excellent and timely article.
The Private airman Certification Standards mentions “Energy Management” eight times under various knowledge elements for stabilized approaches. So pilot applicants can definitely expect to be quizzed on it during their checkrides.
Your comments about “pitch for airspeed, power for altitude” being interrelated is so correct, but implementation of that phrase is often not taught correctly.
Like you, I totally agree that much of the AFH’s Energy Management chapter is way too complex for its intended audience (I wish FAA would use more liberal arts pilots, rather than PhD engineers, to write their documents). Your focus on the “airspeed vs Altitude” chart (AFH Fig 4-11) covers what the pilot needs to understand for nearly all flying regimes.
One minor comment about paragraph 7, where you talk about “total energy is not static; it’s constantly changing. . .”. This is true, but the following discussion only mentions the zero sum of swapping buckets between kinetic and potential energy. Might be beneficial to mention that total energy includes a “finite amount” of chemical energy (gallons of gas on board to be added to kinetic and/or potential energy) and airmass energy (drag to be subtracted from kinetic and/or potential energy).
Again, thanks for writing. Great, Timely Article!!
Useful article.
Despite the truism that our buckets of KE and PE are interchangeable, the swap is NOT without cost The total of KE and PE (and chemical E as well) is ALWAYS less the sum of it’s parts because of losses to drag (and with fuel, inefficies of our engines & thrust creating devices). Testing those statements in relatively areodynamic and also draggy airframes ca be an eye opener in all phases of flight.
I kinda like seeing the math included in the AFH. Though maybe a better place for detail would be in an AC that has a pointer in the AFH energy management chapter references.
Great idea about using an AC in conjunction with the AFH to discuss both the macro and the micro of this complex topic. Hopefully you can get that implemented . I totally agree that those of us with “inquiring minds” need to be able to see the supporting data.
As for your comments about the swap of KE vs PE always having a loss, I am asking for more specifics as I understand total energy to also include drag. The AFH “Figure 4-2. The energy balance equation” shows energy gained by thrust minus energy lost through drag equals change in altitude energy plus change in kinetic energy. Therefore, if you enter a change with “equal thrust and drag,” then climb/descend without changing thrust or drag (other than the resultant change in total drag–induced + parasite– available from graphs similar ones like the PHAK Fig 5-5), does anyone have any data about how significant will that change in drag be?
Your comments are extremely valid. I’m just looking for mathematical data points to be able to explain the magnitude of the change to students–considering primarily the typical type of airplanes low time private pilots will fly.
Thank you for your thoughtful comments.
Don’t lose the forest for the trees, go out and fly and find out for yourself…low time pilots don’t need yet more complex math to define something so basic that even fighter pilots and birds of prey understand the airspeed/altitude trade and how much you get to trade back after diving off the perch.
I vividly remember watching the late Bob Hoover’s energy management performance in the Aero Commander at Valley Field in Tasmania Australia and hearing him discussing the principles after.
If he ever put it into writing it should be compulsory reading for ALL pilots and part of the initial flight training.
Before the 1960’s many instructors first taught power off type landings to new students. This helped teach them relate altitude and airspeed with mass and inertia. Also, every landing was, so to speak, a forced landing, the idea being to never need to add power from before the turn to base all the way to touchdown.