Thought process for Emergency Descents: Vno or Va?

Jaybird180

Jaybird180

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Jaybird180
I think there are merits for each during an Emergency Descent but which one should be favored and why?

Obviously you can point the nose down further at Vno, but at Va, you load the wings at 1G to increase the descent rate and it's possible that you have more controllability. I'm not really sure which one will get you on the ground faster.

This is a theoretical airplane of course, so answers such as "look in the POH" are not considered valid for this discussion.
 
I’d think the REASON for the emergency descent plays a big part in your tactics. On a recent BFR the examiner said, “I smell smoke.” I asked what kind? She was confused by the question, but It makes a difference in how you handle the situation.

If an engine or external fire, there is some chance you’ll be able to blow out the candle, so to speak. In that case, high speed is your friend (and the need to get on the ground as quickly as possible a dire necessity, regardless). If the fire is electrical in the cockpit, you couldn’t use airspeed to blow out the fire in any circumstance. Then, if electrical inside the cockpit or a seat cushion fire, the question is how well do you judge your ability to survive the smoke and maintain cockpit visibility with the ground while making an expedient, but controlled landing.

The worst situation would be a gasoline fire from a fitting inside the cockpit. Then, you’re probably just a passenger on your own personal Roman Candle, regardless of what you do. I hope somebody on the ground gest video.
 
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Yep, it depends.

rhkennerly said:
…The worst situation would be a gasoline fire from a fitting inside the cockpit..
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Counterpoint: lithium battery fire in the vicinity of my lap.
 
TCABM said:
Yep, it depends.
Counterpoint: lithium battery fire in the vicinity of my lap.
Click to expand...

Good point. Still, there is at least some chance you could drop an iPad or laptop out of the window, if you acted quickly. A Li-Batt cooking off behind the panel, like my EFIS backup battery, would be a real **** show.
 
Jaybird180 said:
I think there are merits for each during an Emergency Descent but which one should be favored and why?

Obviously you can point the nose down further at Vno, but at Va, you load the wings at 1G to increase the descent rate and it's possible that you have more controllability. I'm not really sure which one will get you on the ground faster.

This is a theoretical airplane of course, so answers such as "look in the POH" are not considered valid for this discussion.
Click to expand...

Don't understand your comment that at Va you can load the wings to 1G to increase the descent rate. Do you mind explaining what you mean?
 
If in a descent, Vno might be your limit in turbulent air, perhaps if in smooth air you can descend at Vne. You can reduce IAS by loading the wings (bank and pull) and it should give a similar descent rate (???) but without the load on the airframe components that make Vne a limitation.
 
I should also add: Va is the speed at which you can move any single control to full deflection without causing structural damage. It does not mean you can move full lock to full lock, only from neutral to full lock in that single axis only.
 
If there is a good landing area in front of me, I am going to put down full flaps and push the nose down straight ahead, and not too worried about overstressing the flaps. Otherwise, I am lowering the nose about 20 degrees and making a steep spiral to the left, searching for a landing place as we go around. If there are flames, I will turn in whichever direction moves the flames farther away from me.
 
I was taught 45 degree bank, pull to hold the spiral and put the nose down to Vno until ready to level out and land where ever you can. The bank and pull adds a lot of induced drag allowing a more rapid descent (we're trying to dissipate a bunch of potential energy without turning it into kinetic energy) than simply nosing over and holding at Vno or Vne. Have I tested it empirically? Nope. It would be interesting. But the physics make sense to me.

Of course the reason for the descent would matter in how I handled it but if the course of action chosen is get it on the ground (in a survivable piece or pieces) ASAP, that will get you down fast.
 
Depends on your goal. The Airplane Flying Handbook provides some discussion:
The pilot should not allow the airplane’s airspeed to pass the never-exceed speed (VNE), the maximum landing gear extended speed (VLE), or the maximum flap extended speed (VFE), as applicable. In the case of an engine fire, a high airspeed descent could blow out the fire. However, the weakening of the airplane structure is a major concern and descent at low airspeed would place less stress on the airplane. If the descent is conducted in turbulent conditions, the pilot also needs to comply with the design maneuvering speed (VA) limitations. The descent should be made at the maximum allowable airspeed consistent with the procedure used. This provides increased drag and a high rate of descent.
Click to expand...
 

I found this video interesting. I was taught full flaps, top of the white arc, but no flaps, top of the green arc is clearly faster. Ironically I tried this just today, and man you can drop fast. I need to try extending the gear and see if it's faster at gear speed or clean at Vno. Vno is only about 20 knots above my gear speed, and my gear is really draggy, so I'm guessing that will be the fastest.
 
FastEddieB said:
I believe that excludes the rudder.
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Part 23 para 441, "Maneuvering Loads," specifically includes 'vertical surfaces,' i.e. rudder and vertical stabilizer. Full rudder deflection is not part of the definition of Va but the rudder and vertical stab must be able to withstand full deflection 'at speeds up to Va."

Nauga,
stabbed
 
In my eyes there are only two things that warrent the quickest descent in the least amount of time, fire and or major smoke.
You can argue a health issue like a heart attack in there too, but in that case seconds probably won't do much.
Everyone here will have to determine what will get themselves on the ground in the least amount of time. It all depends on the type of plane, single or twin, flaps and gear electric or hydraulic and maybe other considerations (turbulance).
In real life you may have to ignore gear and flap speeds to get the job done. You do what you have to do in real life.
Been there and done that in a C-401 with a engine/fuel fire.
 
Jaybird180 said:
But wait you said
nauga said:
Full rudder deflection is not part of the definition of Va
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Now I'm confused...
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The rest of the sentence you quoted:
nauga said:
...but the rudder and vertical stab must be able to withstand full deflection 'at speeds up to Va."
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The *definition* of Va (23.335) does not talk about rudder deflection, only about stalls and limit normal (vertical) loads; however, per 23.441 the vertical surfaces must be able to withstand full deflection at speeds up to Va.

One of my complaints with the certification process is that requirements like this can get lost in the shotgun pattern of requirements.

Nauga,
and a twisty little maze of passages
 
My best descent rate was Va, full deflection rudder to right, , bank Left to a standard rate turn. Va is maintained in this status by noting the change in INDICATED airspeed when the rudder and bank are done, and holding the new, erroneous indicated airspeed.

This pegged the rate of descent, and with the left bank gave me clear view of the ground below me.
 
FastEddieB said:
I recall that from an airliner that crashed due to excessively fast rudder deflection. My recollection was reading that Va did not include the rudder. Let me investigate - I may be mistaken.

edited to add, this is what I’m recalling: https://www.flyingmag.com/myth-maneuvering-speed/
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That article is about oscillating inputs as the cause of failure that’s not protected by certification.

it’s also the article that made it apparent to me that MacClellan doesn’t read his AFM.
 
FastEddieB said:
I recall that from an airliner that crashed due to excessively fast rudder deflection. My recollection was reading that Va did not include the rudder. Let me investigate - I may be mistaken.

edited to add, this is what I’m recalling: https://www.flyingmag.com/myth-maneuvering-speed/
Click to expand...
23.441 now includes provisions for the type of dynamic overshoot that resulted in the AA587 crash. Again, the definition of Va (23.335) does not 'include the rudder' but 23.441 says that the vertical surfaces (rudder and vstab) must be able to withstand loads under full deflection at Va. What Flying Magazine says or said about it is irrelevant but serves to highlight the risk of assuming one paragraph of a cert basis is sufficient to describe all the criteria that must be met at conditions described in that paragraph.

Nauga,
and his q-beta limit
 
Emergency descent training should be performed as recommended by the manufacturer, including the configuration and airspeeds. Except when prohibited by the manufacturer, the power should be reduced to idle, and the propeller control (if equipped) should be placed in the low pitch (or high revolutions per minute (r.p.m.)) position. This will allow the propeller to act as an aerodynamic brake to help prevent an excessive airspeed buildup during the descent. The landing gear and flaps should be extended as recommended by the manufacturer. This will provide maximum drag so that the descent can be made as rapidly as possible, without excessive airspeed. The pilot should not allow the airplane’s airspeed to pass the never-exceed speed (VNE), the maximum landing gear extended speed (VLE), or the maximum flap extended speed (VFE), as applicable.


In the case of an engine fire, a high airspeed descent could blow out the fire. However, the weakening of the airplane structure is a major concern and descent at low airspeed would place less stress on the airplane. If the descent is conducted in turbulent conditions, the pilot must also comply with the design maneuvering speed (VA) limitations. The descent should be made at the maximum allowable airspeed consistent with the procedure used. This will provide increased drag and therefore the loss of altitude as quickly as possible. The recovery from an emergency descent should be initiated at a high enough altitude to ensure a safe recovery back to level flight or a precautionary landing. When the descent is established and stabilized during training and practice, the descent should be terminated.
 
Clip4 said:
If the descent is conducted in turbulent conditions, the pilot must also comply with the design maneuvering speed (VA) limitations.
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Since we're down in the weeds in the directional axis already, I'll point out that depending on Va to keep you out of trouble in turbulence is unwise if you're below max gross. The speed where stall and limit g happen at the same angle of attack (which is Va at gross weight) goes down as weight decreases, so a big enough gust or full elevator deflection *can* cause an overstress before a stall if you're at book Va but less than gross. Va is a *design* condition a speed at a set of conditions where specific analysis must be conducted, not an everyday or limit flight condition. It's smart to know the number and understand how it should affect your flying, but simply relying on a single value to keep you out of trouble is...unwise.

Nauga,
and his t-shirt collection
 
rhkennerly said:
I’d think the REASON for the emergency descent plays a big part in your tactics. On a recent BFR the examiner said, “I smell smoke.” I asked what kind? She was confused by the question, but It makes a difference in how you handle the situation.

If an engine or external fire, there is some chance you’ll be able to blow out the candle, so to speak. In that case, high speed is your friend (and the need to get on the ground as quickly as possible a dire necessity, regardless). If the fire is electrical in the cockpit, you couldn’t use airspeed to blow out the fire in any circumstance. Then, if electrical inside the cockpit or a seat cushion fire, the question is how well do you judge your ability to survive the smoke and maintain cockpit visibility with the ground while making an expedient, but controlled landing.

The worst situation would be a gasoline fire from a fitting inside the cockpit. Then, you’re probably just a passenger on your own personal Roman Candle, regardless of what you do. I hope somebody on the ground gest video.
Click to expand...


It’s unlikely that you’ll be able to blow out an engine fire in a small aircraft by increasing the airspeed (assuming the wings stay on the plane). It doesn’t even work well in a jet traveling five times as fast.

Shutting off the fuel supply, if possible, is your best bet. You can do nothing about hydraulic and/ or engine oil.

Unlock your doors, fly the airplane until you’re at zero ground speed on the deck, and land the aircraft as soon as possible.
 
I've never understood the "blowing the fire out" concept. How do I know it's out? Just because I can't see it out the window anymore doesn't mean it's necessarily out.

For how to conduct the emergency descent, it very much matters WHY you're making the descent, and what your plan is when you get down to the bottom of the descent, and of course what plane you're flying in.

For instance - if the emergency descent is for a pressurization failure, then probably the "clean high-speed dive" is appropriate (unless the POH says otherwise).
But if the descent is for an engine fire and you plan to land in a field, then doing the clean high-speed dive method is going to result in you now going at high speed when you're trying to set up to land, and therefore have to lose a lot of airspeed, likely throwing off your aim for that field. But if instead you opt for the "Vfe/Vle (whichever is lower), flaps and gear out, 45 degree bank" method, then your airspeed stays lower and once you level off at the bottom the speed will very quickly bleed off to an appropriate approach speed. Like, almost instantly in some airplanes I've tried this in.

Also, definitely do not disregard things like flap speed limits. Although at first it seems like "who cares", you definitely don't want to overspeed the flaps on your descent and end up losing one of them. The resulting roll would be exciting. Also, who knows what structure the fire has weakened (for example, on a multiengine airplane).
 
RussR said:
I've never understood the "blowing the fire out" concept.
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You're not the only one. This comes to mind:

iu


I understand that if the fuel is off and there is nothing more to feed the fire that some high wind might put it out. But there's plenty under the cowl to burn besides fuel ...
 
My C414 POH describes two emergency descents…one (described as the preferred procedure) clean at Vne in smooth conditions @225kcas no bank and another at V gear and flaps extended @ 140kcas 45 deg bank. I’ve done both in the sim and I don’t care how smooth the air seems to be I’m putting gear and flaps down and descending at 140. I don’t want to be flying at Vne when calm, cool and collected. Forget it when under the stress of an emergency descent. The altimeter is spinning and the VSI is pegged down. The Vne procedure doesn’t get you down any faster and the “turbulent” procedure is much more controllable IMHO.
 
I guess part of it may depend on where you’re going at the end of the descent. If you’re landing in whatever’s underneath you, the 45-degree-bank technique has advantages, but if you need to fly a few miles to get someplace landable, the straight-ahead technique has advantages.

Either way, consider your passengers’ response…I head the other day about a passenger who woke up during an emergency descent and thought getting out of the airplane would be preferable.:eek:
 
Not sure if I saw this mentioned:

After getting PPL and starting to learn the plane better I went up to 7000msl (6000agl here). I practiced nose over straight ahead towards Vne and also practiced the bank spiral. I just did the first 3000ft for each. Incredible vertical speed drop for both, obviously. But I felt that spiral left me in more control.

The biggest surprise was how incredibly heavy the controls get as you reach Vne. Wow. I start to wonder if someone was at near 200mph in that dive, had never practiced and then tried pulling back at 500ft agl if they wouldn't just belly right into the ground. I could see someone doing that too trying to sneak thru a hole in the clouds.
 
Jaybird180 said:
I think there are merits for each during an Emergency Descent but which one should be favored and why?
Click to expand...
Just be careful that you don’t descend at too fast of a rate to prevent shock cooling! :stirpot:
 
RyanB said:
Just be careful that you don’t descend at too fast of a rate to prevent shock cooling! :stirpot:
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I suppose if the speed blows the fire out that is a risk…
 
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