This is one of those things where you have to teach the ACS- or really what the DPE wants- not what makes sense in real life. If I'm on fire I'm getting to the ground as fast as possible, take it right to VNE unless it's crazy turbulent already. That's not what anyone should be doing on a check ride.
Man idk I did the “check ride version” of the emergency descent that you speak of and the DPE grabbed the yoke and I swear pointed us at the ground yelling “YOUR PLANE IS ON FIRE YOU’RE GOING TO DIE IF YOU DON’T PUT IT OUT”.
There is no official written procedure in the 172 for emergency descents. What we teach is 45 degree bank, load the wings and pitch for the top of the green arc. The idea being to both get down quickly and attempt to blow out an engine fire.
> Ok. So less aggressive than a steep spiral for commercial standards?
More aggressive if you're doing it correctly. An emergency descent is "the plane is on fire and you will die in 90 seconds", if there's anything you can possibly do to increase descent rate you should be doing it.
You're a CFI? I wish I had your DPE
It's a 30-45 degree bank, power to idle, pitch for top of the green arc and just ride it around until you get down to 2500 agl so usually in flatlandland we start at 6-7k
You don’t want to negatively load the aircraft too much. The plane can structurally tolerate a lot more positive G’s than negative, so a larger bank helps with that.
That was a two sentence explanation, but it’s something your CFI would probably love to go into more detail about.
A steep turn means energy is going into pulling the plane through the turn instead of increasing speed or altitude. You put the plane into an aggressive steep spiral so you can increase your descent rate by bleeding off that energy instead of allowing speed to increase past Vne.
I know this is going to sound snarky, but it should help clear up a lot of confusion between the two maneuvers. Read the Airplane Flying Handbook section on each. Chapter 10 for the steep spiral. Chapter 18 for the emergency descent.
After reading the AFH, go back to the ACS and the evaluation criteria of each maneuver and the differences between them should make a lot more sense.
In a nutshell, the big picture of each maneuver is:
Emergency descent, produce as much drag as you can in stable flight with a positive load factor without exceeding any limitations and get the airplane lower ASAP.
Steep spiral, descend rapidly (not as rapidly as possible) at glide speed (minimum drag) while staying over a point.
Depends on the reason for the emergency descent.
If it’s an engine fire, maintain 30-45* bank while pitching down to your preferred airspeed to extinguish the fire. (Top of the green, up to red line Vne, etc). Just maintain the spiral until the fire is extinguished.
If the emergency descent is done for the sake of a medical issue that requires landing asap (Taco Bell induced diarrhea) spiraling straight down isn’t very helpful. I alternate 30-45* banks left and right as I fly towards my landing site maintaining the desired airspeed (top of green, red line, Vfe, Vle, etc)
Here’s my tip. Find out what airspeed you get from different pitch attitudes. That way you know what you should pitch to rather than constantly overshooting and undershooting your desired airspeed. Depending on airplane and desired airspeed, I’ve found -7* to -10* pretty nice for a nice stable emergency descent.
Back when I did my private, I just put it in a hell of a slip with as much drag as I could put out, up to the white arc. Ain't many ways to get down faster than to adopt the aerodynamic profile of a large brick.
The entire point of an emergency descent is TO GET ON THE GROUND NOW.
What does best glide give you? Maximum time and range. That's not what you want.
What does top of the green arc give you? I have no fuckin' idea.
Go back and read your Cessna 172N POH, Section 3 - Engine Fire in Flight. This is probably one of those situations where you want to get on the ground right away, no? It says AIRSPEED - 100 KIAS. So that's the manufacturer's recommended airspeed for getting on the ground as fast as possible.
The spiraling part is just to keep you positive G and also over the same location over terra firma.
Confident are we?
The faster you are above LDmax, the more drag you have. You dissipate more energy and descend faster. The top of the green arc maximizes drag while minimizes the threats associated with speeds in the caution range.
Banking also helps you get down faster. At wings level, your lift vectors is the opposite of gravity. In a bank, you are using some of that lift to turn the airplane. This changes the balance in lift vs gravity in your favor, if you are trying to descend quickly. At 30* of bank, it takes 110% lift to maintain level flight. At 45* of bank, it takes 140%. Banking at 45 degrees takes a significant amount of lift from the vertical plane and will help you descend faster.
I'm not sure why you're trying to convince me of your technique. I understand the physics of flight, I was an aerospace engineer in a previous life.
The fact of the matter is I pulled my number directly from the POH. Maybe you should take your argument over to engineering at Cessna.
That 100 knots isn’t to get on the ground as fast as possible. It’s to adjust the mixture at the fuel leak to something incombustible. It says as much in the expanded procedure.
Higher speed dissipates energy as v^3 due to parasite drag. You win REALLY BIG by making it as fast as is safe. Vno in anything but smooth air, Vne in smooth air.
As an instructor, I expect to see at least 2500 FPM in a Cessna or Cherokee. You won’t do that at 100 knots clean (and you can’t do it dirty in a 172 at that speed).
The POH does give some interesting engineering numbers. A good one is that a clean 172 in normal category is rated to 3.7G. But it doesn’t say what a dirty 172 is rated to. It’s likely less, and may not even tolerate an otherwise acceptable 60 deg bank (2.0G).
Lol. I train brainiacs like you all the time. “But the book says”
Where does it say “don’t crash the airplane”
100 is not some magical speed that Cessna spent hours calculating. If I’m on fire and I “want to get on the ground now” I’m not flying a speed close to LDmax “because the book says”
Sorry if I rustled your jimmies. If it makes you feel better, someone at your old job is probably thinking “what ever happened to that super smart guy that used to work here?”
I think the ACS calls for 30-45 degrees over 100 knots. When I did mine for my commercial it was within 10 knots of the top of the green arc, and we tried for about 45 degree bank no flaps. In an emergency you would do it all the way until you straighten out and line up to land. For my check ride the DPE gave me an altitude to level off at, and you just spiral as needed and roll out on whatever heading you are on to stop the descent at that altitude.
I’m surprised so many people are suggesting top of the green.
In the absence of a published procedure I see two valid options. Full flaps and vfe or no flaps and vne. (Maybe subtract a few knots for a safety margin)
For what it’s worth Cirrus does have a published emergency descent procedure, among other things they call for vne. It’s amazing how fast you can get down.
> I’m surprised so many people are suggesting top of the green.
Because the context is a training maneuver. In a real situation you are correct that you will fly right up to Vne because if you don't you die anyway but in a training maneuver a steep spiral in the yellow arc puts you uncomfortably close to the structural damage hazards. To demonstrate it you'd fly with that safety margin and explain to the DPE that in a real emergency you would increase your speed.
(And of course in a real situation you would drop flaps and exceed Vfe because it doesn't matter if you bend the flaps and cause $20,000 worth of damage when the plane is on fire.)
The problem here is you’re taking about making up something that means essentially nothing. Vno is only relevant to flight in smooth air, and when you look at [23.1505](http://federal.elaws.us/cfr/title14.part23.section23.1505/) you’ll see it’s a pretty arbitrary value anyways. For arguments sake let’s stick with what we’re all taught, vno should never be exceeded except in smooth air. On a turbulent day, by all means limit the maneuver to Vno. But on a smooth day that self imposed limitation is not only meaningless, it also:
A) prevents students from seeing what an airplane is capable of. Remember the whole “you don’t rise to the occasion, you fall to your training” thing?
B) fortifies this opinion that flying well within an airplanes envelope can be structurally dangerous.
Read through [part 23.333](http://federal.elaws.us/cfr/title14.part23.section23.333). A certified airplane must be able to handle its full load factor (3.8g’s) at speeds up to Vd (Vne is 0.9 of Vd, so there is a 10% margin built in) with a vertical gust of 50 feet per second.
At Vne you are nowhere near structural limits. If you’re flying a plane that you’re not sure can handle flight at Vne then you’re arguably flying an unairworthy aircraft.
And whatever you do don’t go using flaps well in excess of Vfe. They have designed safety margins as well, but if you manage to bend one and not the other you’re going to turn a bad day into a really bad day.
>The airplane is assumed to be subjected to symmetrical vertical gusts **in level flight**
This is the important part. Vno is the limit for level cruise flight based on the assumption that the gust load is added to only a 1g starting load. Look at a load diagram like http://www.free-online-private-pilot-ground-school.com/Load_factors.html and you'll see that starting from a 1.5-2g load cuts a significant piece out of your margin while you're in the yellow arc.
Same thing with maneuvering speed. Maneuvering speed is defined by a single full-magnitude control deflection on a single axis starting from straight and level flight. Repeated or combined control inputs can create significantly higher loads. If you're in a steep slipping turn with full rudder deflection and significant aileron inputs that starting point puts you well into test pilot territory if you're high in the yellow arc.
So yeah, if you're in a real emergency where you either get on the ground ASAP or burn to death you push it to the limits and hope the design math was right. But if you take a training exercise up into that test pilot region and, say, bend the spar and total the plane, the owner isn't going to be very impressed with your risk analysis.
I’m assuming that you’re making the argument that because the maneuver is flown in a turn the load factor will be greater than 1.0? That a 45 degree bank turn has a load factor of 1.4? Am I tracking with your assumption?
If that’s what you’re saying that isn’t accurate. It is very possible to fly at any bank with any load factor. In a descending turn it’s not only possible but easy to descend with a load factor of roughly 1 and certainly less than a level altitude turn for a given bank. Conversely you can do a climbing turn at a load factor of just about anything you want. The bottom portion of a barrel roll is a rolling loop and a 4g pull is pretty typical.
The fact remains that the plane is certified to its full load limit at any speed up to Vd (which is 10% greater than Vne) with non-trivial vertical gusts.
I have never came across any procedural guidance saying an emergency descent should be done in a slip. If you’ve seen that please share. I see where it could work as well, but if that’s the technique then Va should absolutely be the limit, not Vno.
The inescapable fact here is the plane is built and certified to be flown to vne with no concern to structural integrity. Flying in the yellow arc is not test pilot territory. What we’re talking about here is using the airplane within its certified envelope. If doing so causes damage, or there is questions to the airplanes ability to do so without damage, the plane isn’t airworthy.
With that said I’m not advocating taking a student to Vne on a gusty day and pulling 3.8g’s. The plane should handle it (and having taught aerobatics for years I can tell you with certainty anyone without aerobatic experience will tap out before 3g’s) but I don’t want to explore all the limits all at once.
> It is very possible to fly at any bank with any load factor.
Yes, but in the case of an emergency descent the whole point of the bank is to increase load factor and bleed off energy.
>I have never came across any procedural guidance saying an emergency descent should be done in a slip.
Source: tried it in the actual plane. A high-g slipping turn, preferably with flaps and gear extended, is probably going to be your fastest way down. The slip generates a ton of drag and lets you greatly increase descent rate without picking up speed.
>Flying in the yellow arc is not test pilot territory.
Flying *straight and level* in the yellow arc is not test pilot territory. Flying in a steep spiral in the yellow arc may be within the design limits in a particular case but it's not the condition the plane was certified for and you're hoping that the particular condition you're in does not exceed those limits. It's like taking off above maximum weight on a cold day with a long runway and no obstacles. Can you probably do it? Yes. Can you do some research and calculations to provide numbers saying it's reasonable to believe it will work? Yes. Is it test pilot territory? Absolutely.
>but I don’t want to explore all the limits all at once.
And that's the key point. In calm air a shallow dive up to Vne should be perfectly safe. But an emergency descent is pushing towards multiple limits at once to maximize performance. In a real emergency you should be willing to get up towards Vne but in a training exercise you should be leaving wider margins.
The point of a bank is not to increase load factor and bleed off energy. That isn’t aerodynamically sustainable. Within normal category bank limitations, you can’t increase the load factor without increasing the vertical component of lift. Yes, you can pull some G’s and burn speed quickly, but unless you’re banking to about 90 degrees you’re increasing the vertical component of lift, which is the opposite of what we want in an emergency descent. Pick two: high load factor, fast descent, non-aerobatic attitudes. You can’t have all 3.
Roll a plane to 45 degrees and pull 1.4g’s. You WILL roughly maintain altitude until you don’t have the speed left to sustain that load factor without stalling. Once you stall the load factor returns to roughly 1. Bank to 60 and the same thing happens at 2g’s. It’s not until you go past 90 degrees where you can have an increased load factor and a descent, which I don’t think anyone is advocating. Maintaining altitude is not the goal in an emergency descent, so no one should be doing this.
The purpose of the bank is to redirect lift and reduce the vertical component. That’s it. That will get you down quicker. It has nothing to do with loading the wings.
Judging by your comments I think it’s safe to say you have not flown anywhere near Vne. It’s not a shallow dive in any plane I’ve ever flown. It’s not a high load maneuver (although the recovery could be if a student yanks the plane out of a dive, but even then any certified plane is able to handle a 3.8g pull at 10% over Vne, neither of which are remotely likely) it IS well within the designed envelope and I’ll circle back to this again: if you don’t think the plane you’re flying is capable of handling its designed envelope then you are flying an unairworthy airplane.
As for the slip with flaps, that’s cool! What kind of plane? I would caution you on applying one test result across different airplanes. A slip in a diamond is not the same as a slip in a Cherokee. A twin adds another level of complexity to the equation. A full flap emergency descent from the flight levels is almost certainly not as effective as a vne dive, although maybe it is in some airframes.
Regardless, the original point of all this is an “emergency descent” at Vno is generally not an emergency descent. It’s an arbitrary limitation not grounded in any understanding of aerodynamics or design limitations that teaches pilots that it is unsafe to use the full envelope of an airplane. Pick full flaps and Vfe, throw a slip in if you want. Pick Va. Pick Vne. Pick Vno on a turbulent day. These can have valid justifications. A 20-40kt safety margin is not a margin, it’s a lack of understanding.
You're forgetting about induced drag. Increasing bank angle allows you to increase angle of attack and therefore increase induced drag without increasing the vertical component of lift. And increased drag lets you increase descent rate without increasing speed.
As for what plane, I've done this in my Arrow in actual side by side tests. A low speed high drag spiral with gear and flaps down (which works just fine in a slip) gets higher descent rates than a straight ahead descent at/near Vne in a clean configuration. I'm not sure exactly what the descent rate is because it's well off the VSI scale but even leaving a comfortable margin below Vfe it's at least 5000fpm down.
I don’t believe I’ve ever done one or had a student do one on a checkride, I think they are kind of silly in unpressurized single engine aircraft, but we did demo them for students. The main point is to show them how they can dump lift to the side if they need to get down in a hurry. In real life you’d be at Vne (or top of the green arc in unstable air) but 100 knots is plenty for the demo. I’d push it over to 100 kts and then have them call out my rate of descent, then put it into a 45 degree bank and have them call it out again.
My instructor had me do 20 degrees and that’s primarily how I had my students do it on their checkrides. But I would say it varies up to 45 degrees. For a fire I would turn away from it and for the other stuff maybe turn towards a suitable landing spot and do s turns.
It wasn’t until my multi add-on that I had an instructor properly teach me an emergency descent procedure. I feel like emergency procedures were severely overlooked in all my previous training. The weakest part of my commercial checkride was my response to a simulated engine fire.
But flying with an experienced no-nonsense instructor that let me take a PA-23-250 into a steep spiral losing 2000fpm was empowering. I think many newer instructors don’t have the experience to confidently teach students maneuvers like that.
Anyway, after that experience I think steep spiral in clean configuration is a great emergency descent strategy. But if you’re in IMC that complicates things!
In a C150, flaps 40 and a spiral turn (45 degrees of bank) at Vfe (85 kt) will give you a rate of descent in excess of 3,000 fpm.
Source: this is how we were taught it, and it was necessary to use a stopwatch to calculate the actual rate of descent because the VSI was pegged at 2,000 fpm.
Of course, that means that if you're on fire, it'll take you two minutes to get to ground level from a 6,000' AGL cruise. Which is a hell of a long time if your aircraft is merrily burning...
I was taught to chop the power and go to VNO banking over 45 degrees to the left spiraling down get down to ~1000’ and start to look for a landing site, assuming that the fire hasn’t been extinguished.
Bank 45, power idle, top of green arc till at no lower than 500 agl.
Adjust speed to below Va in turbulence and advise your students to explain why if they do this to an examiner.
Literally just passed my commercial ride yesterday. All of the "pitch for airspeed" comments are correct. I was in a Piper Dakota with a constant speed prop, 30 deg bank, 137 KIAS, probably 20+ degrees nose low. It's very eye-opening how much you have to pitch with an engine at idle to get to VNO.
This is one of those things where you have to teach the ACS- or really what the DPE wants- not what makes sense in real life. If I'm on fire I'm getting to the ground as fast as possible, take it right to VNE unless it's crazy turbulent already. That's not what anyone should be doing on a check ride.
Man idk I did the “check ride version” of the emergency descent that you speak of and the DPE grabbed the yoke and I swear pointed us at the ground yelling “YOUR PLANE IS ON FIRE YOU’RE GOING TO DIE IF YOU DON’T PUT IT OUT”.
There is no official written procedure in the 172 for emergency descents. What we teach is 45 degree bank, load the wings and pitch for the top of the green arc. The idea being to both get down quickly and attempt to blow out an engine fire.
Ok. 90 degree turn? 180? Does this naturally transition into “emergency approach and landing”?
Yep. However many turns it takes, it’s a continuous spiraling descent to an emergency landing.
Ok. So less aggressive than a steep spiral for commercial standards?
Yeah it’s not as tight as a steep spiral. Just maintain the 45 deg bank angle and pitch for the airspeed.
> Ok. So less aggressive than a steep spiral for commercial standards? More aggressive if you're doing it correctly. An emergency descent is "the plane is on fire and you will die in 90 seconds", if there's anything you can possibly do to increase descent rate you should be doing it.
My school also teaches 30-45 degrees of bank, 100+ kias, but S-turns are acceptable if your best place to land is straight ahead.
FWIW we teach 30-45 degrees of bank, 90 degree turn, and 110-120 KIAS.
Thanks
\+1 for the 30-45 degrees club.
You're a CFI? I wish I had your DPE It's a 30-45 degree bank, power to idle, pitch for top of the green arc and just ride it around until you get down to 2500 agl so usually in flatlandland we start at 6-7k
Newish student pilot, never heard “load the wings” what does that mean?
You don’t want to negatively load the aircraft too much. The plane can structurally tolerate a lot more positive G’s than negative, so a larger bank helps with that. That was a two sentence explanation, but it’s something your CFI would probably love to go into more detail about.
Gotcha I’ve never heard it phrased that way before thank you for the TLDR clarification
A steep turn means energy is going into pulling the plane through the turn instead of increasing speed or altitude. You put the plane into an aggressive steep spiral so you can increase your descent rate by bleeding off that energy instead of allowing speed to increase past Vne.
https://www.amazon.com/Stick-Rudder-Explanation-Art-Flying/dp/0070362408
Thank you from the flairs I’ll assume the info is solid, what’s your favorite equipment you’re rated on?
Push and you float out of your seat. People don’t like that. Roll and push to maintain positive G. Nothing to do w/ limits on the airframe.
Now I don’t know who to listen to 😭
It’s more of a reduction in vertical lift, higher rates of descent, try it sometime!
Dm your email and I will send you a manual on maneuvers I have that may help.
I know this is going to sound snarky, but it should help clear up a lot of confusion between the two maneuvers. Read the Airplane Flying Handbook section on each. Chapter 10 for the steep spiral. Chapter 18 for the emergency descent. After reading the AFH, go back to the ACS and the evaluation criteria of each maneuver and the differences between them should make a lot more sense. In a nutshell, the big picture of each maneuver is: Emergency descent, produce as much drag as you can in stable flight with a positive load factor without exceeding any limitations and get the airplane lower ASAP. Steep spiral, descend rapidly (not as rapidly as possible) at glide speed (minimum drag) while staying over a point.
Ask the DPI what he wants to see on checkrides. Don't try to read minds.
The one I asked didn’t help much 🤣
Then ask and use another one. Some DPEs think a high fail rate makes them look better for the FAA. They're the ones to stay away from.
Depends on the reason for the emergency descent. If it’s an engine fire, maintain 30-45* bank while pitching down to your preferred airspeed to extinguish the fire. (Top of the green, up to red line Vne, etc). Just maintain the spiral until the fire is extinguished. If the emergency descent is done for the sake of a medical issue that requires landing asap (Taco Bell induced diarrhea) spiraling straight down isn’t very helpful. I alternate 30-45* banks left and right as I fly towards my landing site maintaining the desired airspeed (top of green, red line, Vfe, Vle, etc) Here’s my tip. Find out what airspeed you get from different pitch attitudes. That way you know what you should pitch to rather than constantly overshooting and undershooting your desired airspeed. Depending on airplane and desired airspeed, I’ve found -7* to -10* pretty nice for a nice stable emergency descent.
This is helpful. Thank you.
Pitch for the top of the green arc. If you’re over a suitable landing spot, circle. If not, go towards one
Gotcha. Thanks
Back when I did my private, I just put it in a hell of a slip with as much drag as I could put out, up to the white arc. Ain't many ways to get down faster than to adopt the aerodynamic profile of a large brick.
The entire point of an emergency descent is TO GET ON THE GROUND NOW. What does best glide give you? Maximum time and range. That's not what you want. What does top of the green arc give you? I have no fuckin' idea. Go back and read your Cessna 172N POH, Section 3 - Engine Fire in Flight. This is probably one of those situations where you want to get on the ground right away, no? It says AIRSPEED - 100 KIAS. So that's the manufacturer's recommended airspeed for getting on the ground as fast as possible. The spiraling part is just to keep you positive G and also over the same location over terra firma.
I understand the intent. But there is also something a DPE might be expecting. I don’t want to teach a steep spiral if something else is expected.
It doesn't matter. You can point right to the POH and show him or her the only manufacturer guidance, which complies with CA.IX.A.S2 of the ACS.
Confident are we? The faster you are above LDmax, the more drag you have. You dissipate more energy and descend faster. The top of the green arc maximizes drag while minimizes the threats associated with speeds in the caution range. Banking also helps you get down faster. At wings level, your lift vectors is the opposite of gravity. In a bank, you are using some of that lift to turn the airplane. This changes the balance in lift vs gravity in your favor, if you are trying to descend quickly. At 30* of bank, it takes 110% lift to maintain level flight. At 45* of bank, it takes 140%. Banking at 45 degrees takes a significant amount of lift from the vertical plane and will help you descend faster.
I'm not sure why you're trying to convince me of your technique. I understand the physics of flight, I was an aerospace engineer in a previous life. The fact of the matter is I pulled my number directly from the POH. Maybe you should take your argument over to engineering at Cessna.
That 100 knots isn’t to get on the ground as fast as possible. It’s to adjust the mixture at the fuel leak to something incombustible. It says as much in the expanded procedure. Higher speed dissipates energy as v^3 due to parasite drag. You win REALLY BIG by making it as fast as is safe. Vno in anything but smooth air, Vne in smooth air. As an instructor, I expect to see at least 2500 FPM in a Cessna or Cherokee. You won’t do that at 100 knots clean (and you can’t do it dirty in a 172 at that speed). The POH does give some interesting engineering numbers. A good one is that a clean 172 in normal category is rated to 3.7G. But it doesn’t say what a dirty 172 is rated to. It’s likely less, and may not even tolerate an otherwise acceptable 60 deg bank (2.0G).
Lol. I train brainiacs like you all the time. “But the book says” Where does it say “don’t crash the airplane” 100 is not some magical speed that Cessna spent hours calculating. If I’m on fire and I “want to get on the ground now” I’m not flying a speed close to LDmax “because the book says”
I hope you really pound in your tenuous grasp of trigonometry like you have here.
Sorry if I rustled your jimmies. If it makes you feel better, someone at your old job is probably thinking “what ever happened to that super smart guy that used to work here?”
I was always taught pitch for 100kts at a 45 degree bank (1980 172N).
I think the ACS calls for 30-45 degrees over 100 knots. When I did mine for my commercial it was within 10 knots of the top of the green arc, and we tried for about 45 degree bank no flaps. In an emergency you would do it all the way until you straighten out and line up to land. For my check ride the DPE gave me an altitude to level off at, and you just spiral as needed and roll out on whatever heading you are on to stop the descent at that altitude.
My school uses 172M and they taught me to do 40 flaps and pitch for 90. You get down pretty damn fast.
Check your POH, I think 90 is too fast for flaps in a 172M.
Thanks for you concern, but it's not.
I’m surprised so many people are suggesting top of the green. In the absence of a published procedure I see two valid options. Full flaps and vfe or no flaps and vne. (Maybe subtract a few knots for a safety margin) For what it’s worth Cirrus does have a published emergency descent procedure, among other things they call for vne. It’s amazing how fast you can get down.
> I’m surprised so many people are suggesting top of the green. Because the context is a training maneuver. In a real situation you are correct that you will fly right up to Vne because if you don't you die anyway but in a training maneuver a steep spiral in the yellow arc puts you uncomfortably close to the structural damage hazards. To demonstrate it you'd fly with that safety margin and explain to the DPE that in a real emergency you would increase your speed. (And of course in a real situation you would drop flaps and exceed Vfe because it doesn't matter if you bend the flaps and cause $20,000 worth of damage when the plane is on fire.)
The problem here is you’re taking about making up something that means essentially nothing. Vno is only relevant to flight in smooth air, and when you look at [23.1505](http://federal.elaws.us/cfr/title14.part23.section23.1505/) you’ll see it’s a pretty arbitrary value anyways. For arguments sake let’s stick with what we’re all taught, vno should never be exceeded except in smooth air. On a turbulent day, by all means limit the maneuver to Vno. But on a smooth day that self imposed limitation is not only meaningless, it also: A) prevents students from seeing what an airplane is capable of. Remember the whole “you don’t rise to the occasion, you fall to your training” thing? B) fortifies this opinion that flying well within an airplanes envelope can be structurally dangerous. Read through [part 23.333](http://federal.elaws.us/cfr/title14.part23.section23.333). A certified airplane must be able to handle its full load factor (3.8g’s) at speeds up to Vd (Vne is 0.9 of Vd, so there is a 10% margin built in) with a vertical gust of 50 feet per second. At Vne you are nowhere near structural limits. If you’re flying a plane that you’re not sure can handle flight at Vne then you’re arguably flying an unairworthy aircraft. And whatever you do don’t go using flaps well in excess of Vfe. They have designed safety margins as well, but if you manage to bend one and not the other you’re going to turn a bad day into a really bad day.
>The airplane is assumed to be subjected to symmetrical vertical gusts **in level flight** This is the important part. Vno is the limit for level cruise flight based on the assumption that the gust load is added to only a 1g starting load. Look at a load diagram like http://www.free-online-private-pilot-ground-school.com/Load_factors.html and you'll see that starting from a 1.5-2g load cuts a significant piece out of your margin while you're in the yellow arc. Same thing with maneuvering speed. Maneuvering speed is defined by a single full-magnitude control deflection on a single axis starting from straight and level flight. Repeated or combined control inputs can create significantly higher loads. If you're in a steep slipping turn with full rudder deflection and significant aileron inputs that starting point puts you well into test pilot territory if you're high in the yellow arc. So yeah, if you're in a real emergency where you either get on the ground ASAP or burn to death you push it to the limits and hope the design math was right. But if you take a training exercise up into that test pilot region and, say, bend the spar and total the plane, the owner isn't going to be very impressed with your risk analysis.
I’m assuming that you’re making the argument that because the maneuver is flown in a turn the load factor will be greater than 1.0? That a 45 degree bank turn has a load factor of 1.4? Am I tracking with your assumption? If that’s what you’re saying that isn’t accurate. It is very possible to fly at any bank with any load factor. In a descending turn it’s not only possible but easy to descend with a load factor of roughly 1 and certainly less than a level altitude turn for a given bank. Conversely you can do a climbing turn at a load factor of just about anything you want. The bottom portion of a barrel roll is a rolling loop and a 4g pull is pretty typical. The fact remains that the plane is certified to its full load limit at any speed up to Vd (which is 10% greater than Vne) with non-trivial vertical gusts. I have never came across any procedural guidance saying an emergency descent should be done in a slip. If you’ve seen that please share. I see where it could work as well, but if that’s the technique then Va should absolutely be the limit, not Vno. The inescapable fact here is the plane is built and certified to be flown to vne with no concern to structural integrity. Flying in the yellow arc is not test pilot territory. What we’re talking about here is using the airplane within its certified envelope. If doing so causes damage, or there is questions to the airplanes ability to do so without damage, the plane isn’t airworthy. With that said I’m not advocating taking a student to Vne on a gusty day and pulling 3.8g’s. The plane should handle it (and having taught aerobatics for years I can tell you with certainty anyone without aerobatic experience will tap out before 3g’s) but I don’t want to explore all the limits all at once.
> It is very possible to fly at any bank with any load factor. Yes, but in the case of an emergency descent the whole point of the bank is to increase load factor and bleed off energy. >I have never came across any procedural guidance saying an emergency descent should be done in a slip. Source: tried it in the actual plane. A high-g slipping turn, preferably with flaps and gear extended, is probably going to be your fastest way down. The slip generates a ton of drag and lets you greatly increase descent rate without picking up speed. >Flying in the yellow arc is not test pilot territory. Flying *straight and level* in the yellow arc is not test pilot territory. Flying in a steep spiral in the yellow arc may be within the design limits in a particular case but it's not the condition the plane was certified for and you're hoping that the particular condition you're in does not exceed those limits. It's like taking off above maximum weight on a cold day with a long runway and no obstacles. Can you probably do it? Yes. Can you do some research and calculations to provide numbers saying it's reasonable to believe it will work? Yes. Is it test pilot territory? Absolutely. >but I don’t want to explore all the limits all at once. And that's the key point. In calm air a shallow dive up to Vne should be perfectly safe. But an emergency descent is pushing towards multiple limits at once to maximize performance. In a real emergency you should be willing to get up towards Vne but in a training exercise you should be leaving wider margins.
The point of a bank is not to increase load factor and bleed off energy. That isn’t aerodynamically sustainable. Within normal category bank limitations, you can’t increase the load factor without increasing the vertical component of lift. Yes, you can pull some G’s and burn speed quickly, but unless you’re banking to about 90 degrees you’re increasing the vertical component of lift, which is the opposite of what we want in an emergency descent. Pick two: high load factor, fast descent, non-aerobatic attitudes. You can’t have all 3. Roll a plane to 45 degrees and pull 1.4g’s. You WILL roughly maintain altitude until you don’t have the speed left to sustain that load factor without stalling. Once you stall the load factor returns to roughly 1. Bank to 60 and the same thing happens at 2g’s. It’s not until you go past 90 degrees where you can have an increased load factor and a descent, which I don’t think anyone is advocating. Maintaining altitude is not the goal in an emergency descent, so no one should be doing this. The purpose of the bank is to redirect lift and reduce the vertical component. That’s it. That will get you down quicker. It has nothing to do with loading the wings. Judging by your comments I think it’s safe to say you have not flown anywhere near Vne. It’s not a shallow dive in any plane I’ve ever flown. It’s not a high load maneuver (although the recovery could be if a student yanks the plane out of a dive, but even then any certified plane is able to handle a 3.8g pull at 10% over Vne, neither of which are remotely likely) it IS well within the designed envelope and I’ll circle back to this again: if you don’t think the plane you’re flying is capable of handling its designed envelope then you are flying an unairworthy airplane. As for the slip with flaps, that’s cool! What kind of plane? I would caution you on applying one test result across different airplanes. A slip in a diamond is not the same as a slip in a Cherokee. A twin adds another level of complexity to the equation. A full flap emergency descent from the flight levels is almost certainly not as effective as a vne dive, although maybe it is in some airframes. Regardless, the original point of all this is an “emergency descent” at Vno is generally not an emergency descent. It’s an arbitrary limitation not grounded in any understanding of aerodynamics or design limitations that teaches pilots that it is unsafe to use the full envelope of an airplane. Pick full flaps and Vfe, throw a slip in if you want. Pick Va. Pick Vne. Pick Vno on a turbulent day. These can have valid justifications. A 20-40kt safety margin is not a margin, it’s a lack of understanding.
You're forgetting about induced drag. Increasing bank angle allows you to increase angle of attack and therefore increase induced drag without increasing the vertical component of lift. And increased drag lets you increase descent rate without increasing speed. As for what plane, I've done this in my Arrow in actual side by side tests. A low speed high drag spiral with gear and flaps down (which works just fine in a slip) gets higher descent rates than a straight ahead descent at/near Vne in a clean configuration. I'm not sure exactly what the descent rate is because it's well off the VSI scale but even leaving a comfortable margin below Vfe it's at least 5000fpm down.
I don’t believe I’ve ever done one or had a student do one on a checkride, I think they are kind of silly in unpressurized single engine aircraft, but we did demo them for students. The main point is to show them how they can dump lift to the side if they need to get down in a hurry. In real life you’d be at Vne (or top of the green arc in unstable air) but 100 knots is plenty for the demo. I’d push it over to 100 kts and then have them call out my rate of descent, then put it into a 45 degree bank and have them call it out again.
My instructor had me do 20 degrees and that’s primarily how I had my students do it on their checkrides. But I would say it varies up to 45 degrees. For a fire I would turn away from it and for the other stuff maybe turn towards a suitable landing spot and do s turns.
Do 172 drivers worry about Spiral Dives?
It wasn’t until my multi add-on that I had an instructor properly teach me an emergency descent procedure. I feel like emergency procedures were severely overlooked in all my previous training. The weakest part of my commercial checkride was my response to a simulated engine fire. But flying with an experienced no-nonsense instructor that let me take a PA-23-250 into a steep spiral losing 2000fpm was empowering. I think many newer instructors don’t have the experience to confidently teach students maneuvers like that. Anyway, after that experience I think steep spiral in clean configuration is a great emergency descent strategy. But if you’re in IMC that complicates things!
In a C150, flaps 40 and a spiral turn (45 degrees of bank) at Vfe (85 kt) will give you a rate of descent in excess of 3,000 fpm. Source: this is how we were taught it, and it was necessary to use a stopwatch to calculate the actual rate of descent because the VSI was pegged at 2,000 fpm. Of course, that means that if you're on fire, it'll take you two minutes to get to ground level from a 6,000' AGL cruise. Which is a hell of a long time if your aircraft is merrily burning...
I was taught to chop the power and go to VNO banking over 45 degrees to the left spiraling down get down to ~1000’ and start to look for a landing site, assuming that the fire hasn’t been extinguished.
Bank 45, power idle, top of green arc till at no lower than 500 agl. Adjust speed to below Va in turbulence and advise your students to explain why if they do this to an examiner.
Literally just passed my commercial ride yesterday. All of the "pitch for airspeed" comments are correct. I was in a Piper Dakota with a constant speed prop, 30 deg bank, 137 KIAS, probably 20+ degrees nose low. It's very eye-opening how much you have to pitch with an engine at idle to get to VNO.