Emergency Descents

Mistake Not... said:
I may be thinking about this wrong, but we're trying for the highest sustainable descent rate, right? Whatever IAS and config gives us that, correct?

Or are there other issues that factor in?
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That was my original question. What are the 'numbers' on that. If you just need to get to a lower altitude ASAP, then whatever gets you down faster is what you want. But if you need to get down and land, then there is more to the picture.
 
luvflyin said:
What's your gut feeling. In your slippery ol' Mooney, say at about 8000 AGL, no fire but you need on the ground ASAP. How would you do it. What is Vfe and Vlo for a M20c
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In my aircraft gear comes down at 120 (mph) and flaps at 105. What I'll do depends on the nature of the emergency. If the emergency comes from the pax and not he airplane, then I'll pull back the power and pitch up until I hit Vlo. Gear comes down, flaps shortly thereafter. I think I'd then put it in a spiral dive below Vfe to get down. Probably keep it in a pronounced slip the whole time.

If something has gone wrong with the airplane necessitating an emergency descent, it belongs to the insurance company. I'll probably to the same stuff, but won't be so nice about staying below Vfe on the way down.
 
luvflyin said:
If you just need to get to a lower altitude ASAP, then whatever gets you down faster is what you want. But if you need to get down and land, then there is more to the picture.
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Yeah if it's an O2 problem, if you're that high, yes get down ASAP. Usually to 10K. But having to land once you get down, then what's the trade off in time between Vno (slowing and configuring) and Vfe(already configured) descents?
 
mscard88 said:
Yeah if it's an O2 problem, if you're that high, yes get down ASAP. Usually to 10K. But having to land once you get down, then what's the trade off in time between Vno (slowing and configuring) and Vfe(already configured) descents?
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That's probably going to be 'model specific.' I can certainly see why the FAA's recommended procedure is what it is for PPL checkride. Having a freshly minted 50 hour pilot toying around with Vne probably isn't such a good idea.
 
mscard88 said:
One benefit of Vfe I think is when you level off to land you're already configured w/ flaps and can slow quicker. So I'm wondering that time gained of being configured at Vfe would cancel out the time of Vno, while quicker downhill, which would will require a bit more time to slow and configure for landing. Guess I need to make up a 5x7 card w/ different configurations and fly it. Thoughts?
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I used a 3x5 card to guide and take notes while practicing slow flight configurations at altitude...so other than the vehement card size disagreement between us, I agree. Go do it and report back...
 
455 Bravo Uniform said:
I used a 3x5 card to guide and take notes while practicing slow flight configurations at altitude...so other than the vehement card size disagreement between us, I agree. Go do it and report back...
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Well, if I do then that means mine is BIGGER than yours right? :D
 
You've flown bigger planes than I, so I assumed that anyway, lol.
 
luvflyin said:
That's probably going to be 'model specific.' I can certainly see why the FAA's recommended procedure is what it is for PPL checkride. Having a freshly minted 50 hour pilot toying around with Vne probably isn't such a good idea.
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They don't even let ATPs toy around with Vne...when turbine airplanes descend at max airspeed, Vmo/Mmo is the structural equivalent of Vno (top of the green arc) in a piston airplane.
 
flyingron said:
Fire is a biggie for everyone.
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Well yes, fire is an emergency landing for everyone, but not necessarily an emergency descent from altitude (we call it a high dive).
Really that almost pinpoints it to rapid/explosive decompression.
 
I've seen several comment that they would push Vne or Vfe because its an emergency, or the insurance company already has the airplane, etc. In my opinion, that may be overreacting to the actual emergency, and letting emergency A turn into emergency B,C, and D because you have now overstressed the aircraft in reacting to the first emergency.

When we were doing descents for both my CSEL and CMEL, we did it gear down and flaps up, and kept the speed near, but not over, the max gear extended speed.

At the end of the day, the goal is to lose altitude quickly, but safely, and I doubt there is a huge difference on time to decent based on configuration. The key is to do it controlled, and within the flight envelope. I just don't see the need to exceed the operating limitations during an emergency that doesn't require it.
 
luvflyin said:
That was my original question. What are the 'numbers' on that.
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We ran the test with my friend and were surprised at the results.
While it seems that everyone here is pushing the dirty configuration with no data to back it up, the clean Vne descent was much faster (almost 2x) than the dirty configuration.
Logically, a smart pilot would not want to overstress the airplane in daytime heating turbulence so one should choose Vno over Vne. And we were on the ground still faster than the dirty airplane.
IIRC, the vertical speeds we saw were as follows:
- 1500fpm dirty @ Vfe
- 1900fpm clean @ Vno
- 2000+fpm clean @ Vne (my VSI's range is -2000fpm to 2000fpm, sorry)

As you might have already thought of, the dirty descent would be sped up by applying an aggressive slip. Depending on the aircraft, it might not be allowed, though, with full flaps. But I believe more aircraft allow it than not, check our POH. Note: one cannot slip in fast clean descent because one is likely above Va already.

In the fast and clean configurations, I would level off on DW and slow down to Vge, drop the gear and start adding flaps. I was at Vfe in mere seconds and then turned toward the rwy to land. But I was still landing about 1/2 minute earlier than I did in dirty configuration.
These results are for a C77R so no speed brakes or 40-degree flaps. It would be interesting to perform the test on my buddy's Bo or a 182 with 40 flaps.

Has anybody else tested these scenarios?
 
Autorotate-2,000 FPM.
 
BigBadLou said:
We ran the test with my friend and were surprised at the results.
While it seems that everyone here is pushing the dirty configuration with no data to back it up, the clean Vne descent was much faster (almost 2x) than the dirty configuration.
Logically, a smart pilot would not want to overstress the airplane in daytime heating turbulence so one should choose Vno over Vne. And we were on the ground still faster than the dirty airplane.
IIRC, the vertical speeds we saw were as follows:
- 1500fpm dirty @ Vfe
- 1900fpm clean @ Vno
- 2000+fpm clean @ Vne (my VSI's range is -2000fpm to 2000fpm, sorry)

As you might have already thought of, the dirty descent would be sped up by applying an aggressive slip. Depending on the aircraft, it might not be allowed, though, with full flaps. But I believe more aircraft allow it than not, check our POH. Note: one cannot slip in fast clean descent because one is likely above Va already.

In the fast and clean configurations, I would level off on DW and slow down to Vge, drop the gear and start adding flaps. I was at Vfe in mere seconds and then turned toward the rwy to land. But I was still landing about 1/2 minute earlier than I did in dirty configuration.
These results are for a C77R so no speed brakes or 40-degree flaps. It would be interesting to perform the test on my buddy's Bo or a 182 with 40 flaps.

Has anybody else tested these scenarios?
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Were your tests with spiral or level descent?
 
BigBadLou said:
While it seems that everyone here is pushing the dirty configuration with no data to back it up, the clean Vne descent was much faster (almost 2x) than the dirty configuration.
Logically, a smart pilot would not want to overstress the airplane in daytime heating turbulence so one should choose Vno over Vne. And we were on the ground still faster than the dirty airplane.
IIRC, the vertical speeds we saw were as follows
Click to expand...
Thanks, this makes sense since that's what the Cirrus transition course taught as well for emergency descent. Clean airplane at Vne, or if any significant turbulence is expected then Vno.

I think people have a (mis)conception that dirty descends "faster" because you can get a steep descent angle out of it and "drop it in" to the airport. But if you just want to get down fast than clean is the way to go. Thanks for the real life test data to back it up!

**For any helicopter pilots out there, what's the technique there?
 
midwestpa24 said:
I've seen several comment that they would push Vne or Vfe because its an emergency, or the insurance company already has the airplane, etc. In my opinion, that may be overreacting to the actual emergency, and letting emergency A turn into emergency B,C, and D because you have now overstressed the aircraft in reacting to the first emergency.

When we were doing descents for both my CSEL and CMEL, we did it gear down and flaps up, and kept the speed near, but not over, the max gear extended speed.

At the end of the day, the goal is to lose altitude quickly, but safely, and I doubt there is a huge difference on time to decent based on configuration. The key is to do it controlled, and within the flight envelope. I just don't see the need to exceed the operating limitations during an emergency that doesn't require it.
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I agree, and I was originally taught the same way. Gear down and descend at max gear extension speed. I think that is probably the best choice since you'll be in a configuration where you could land if needed.

BUT, you'll get a much higher rate of descent if you pull the throttles back to idle and descend at Vno, and aren't really in a configuration that would overstress the airplane (as long as no real abrupt control inputs are performed above Va). Unfortunately you're not really set up to land that way.

At the end of the day, all this discussion is essentially a waste in my opinion. Do the emergency descent in the configuration called out in the Airplane Flying Handbook, ACS, and/or the flight manual for the airplane. An examiner is going to have a hard time failing someone for doing it that way.
 
Tantalum said:
Thanks, this makes sense since that's what the Cirrus transition course taught as well for emergency descent. Clean airplane at Vne, or if any significant turbulence is expected then Vno.

I think people have a (mis)conception that dirty descends "faster" because you can get a steep descent angle out of it and "drop it in" to the airport. But if you just want to get down fast than clean is the way to go. Thanks for the real life test data to back it up!

**For any helicopter pilots out there, what's the technique there?
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You could autorotate like I said above but unless it's in the flight manual, it's up to the pilot.

The only two flight manuals I have on hand (UH-60, B407) don't specify a procedure for an emergency descent and neither does the PTS. For instance, for engine/electric fires its essentially attempt to put out the fire and LAND AS SOON AS POSSIBLE. How that's done is up to the pilot and the limitations on the type aircraft. A straight ahead auto will result in roughly 1800-2200 FPM. In a spiral descent you could easily blow right through VNE in 30 degree nose down and well over 4,000 FPM. Depending on aircraft type, you could could also easily overspeed the rotor/engine in a spiral down. I suppose if it's a true emergency, exceeding a limit wouldn't be a major concern, but you also want to keep spinning parts attached to the helo.
 
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BigBadLou said:
We ran the test with my friend and were surprised at the results.
While it seems that everyone here is pushing the dirty configuration with no data to back it up, the clean Vne descent was much faster (almost 2x) than the dirty configuration.
Logically, a smart pilot would not want to overstress the airplane in daytime heating turbulence so one should choose Vno over Vne. And we were on the ground still faster than the dirty airplane.
IIRC, the vertical speeds we saw were as follows:
- 1500fpm dirty @ Vfe
- 1900fpm clean @ Vno
- 2000+fpm clean @ Vne (my VSI's range is -2000fpm to 2000fpm, sorry)

As you might have already thought of, the dirty descent would be sped up by applying an aggressive slip. Depending on the aircraft, it might not be allowed, though, with full flaps. But I believe more aircraft allow it than not, check our POH. Note: one cannot slip in fast clean descent because one is likely above Va already.

In the fast and clean configurations, I would level off on DW and slow down to Vge, drop the gear and start adding flaps. I was at Vfe in mere seconds and then turned toward the rwy to land. But I was still landing about 1/2 minute earlier than I did in dirty configuration.
These results are for a C77R so no speed brakes or 40-degree flaps. It would be interesting to perform the test on my buddy's Bo or a 182 with 40 flaps.

Has anybody else tested these scenarios?
Click to expand...
Thats good info. Thanks. Vlo around 120knots on a 177rg helps. Might not be as big a difference on fixed gear planes. On the Va thing, isn't that about 'abrupt' movement of the control surfaces? I wouldn't think gently putting it into a slip without slamming your foot to the floor would be a problem. I think slammin the elevator around is the controlling factor on setting Va, but thats just a gut feeling, I don't know. I'm going to be getting a Flight Review in a couple months. I'll have some numbers for C172 after that.
 
Emergency Descents on the PP PTS/ACS have pretty much come full circle. When I did them in 1988, the Scenerio usually was you got stuck on top of a cloud layer and found a hole to descend through. So the Full Flap Spiral Down configuration was usually recommended. Then for a number of years the Spiral/ Turning Descent was removed from the PTS and it was just demonstate, "The examiner is having a heart attack" and you need to get him down to Paramedics waiting on the ground. So just set up a high rate of descent, Spiraling optional.

The current ACS asks the applicant to maintain a 30-45 bank angle during the Descent. Best argument I can come up with for this is that you do get a higher descent rate while turning.

Examiners lately like the Scenario based training of a Fire, because they can get the applicant to demonstrate several tasks in essentially one maneuver/scenario. It covers a good portion of "Systems and Equipment Malfunctions", "Emergency Descent", and "Emergency Approach and Landing".

Plus it isn't the typical your engine just quit, because you handle it differently than you would a fire.

Brian
CFIIG/ASEL
 
Just for reference, here is what the C172N Manual says....
ENGINE FIRE IN FLIGHT

Mixture -- IDLE CUT-OFF.
Fuel Selector Valve -- OFF.
Master Switch -- OFF.
Cabin Heat and Air -- OFF (except overhead vents).
Airspeed -- 100 KIAS (If fire is not extinguished, increase glide
speed to find an airspeed which will provide an incombustible
mixture).
Forced Landing -- EXECUTE (as described in Emergency Landing
Without Engine Power)
 
brcase said:
The current ACS asks the applicant to maintain a 30-45 bank angle during the Descent. Best argument I can come up with for this is that you do get a higher descent rate while turning.
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The purpose of the 45° bank is to maintain positive load factor and thus is only used during the entry, unless it is necessary to turn to look for traffic or look for a landing site.
 
It’s good to know I am not the only one somewhat confused by this. During my recent commercial check ride I got this kind of screwed up. The examiner said I was on fire so he wanted a very fast airspeed decent. I gave him a somewhat fast a steep spiral.

I passed, so I guess it was good enough, but he said I could have done better.
 
luvflyin said:
On the Va thing, isn't that about 'abrupt' movement of the control surfaces? I wouldn't think gently putting it into a slip without slamming your foot to the floor would be a problem. I think slammin the elevator around is the controlling factor on setting Va, but thats just a gut feeling, I don't know.
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Va is "maneuvering speed" and it is speed past which it is not recommended to make a full deflection of any control surface. Doing so past Va could result in overstressing the airframe.
So it is not about how abruptly you apply the control pressure but about whether you make a full deflection.
 
Did something like that for a living for a while.

Power back to the bottom of the green, lean for CHTs, cowl flaps closed, prop forward end of green

clean

Pitch for just shy of vne

Turn as little as possible

For landing, downwind level off

60 degree + base to final decel turn to vle, to vfe, to slip, cross the fence at vref, straighten out and chirp the mains, hold the nose wheel (or Tailwheel for the men reading) off till the first taxiway, exit the aircraft and wrap it up with a scotch older than your date.
 
James331 said:
Did something like that for a living for a while.

Power back to the bottom of the green, lean for CHTs, cowl flaps closed, prop forward end of green

clean

Pitch for just shy of vne

Turn as little as possible

For landing, downwind level off

60 degree + base to final decel turn to vle, to vfe, to slip, cross the fence at vref, straighten out and chirp the mains, hold the nose wheel (or Tailwheel for the men reading) off till the first taxiway, exit the aircraft and wrap it up with a scotch older than your date.
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What airplane?
 
BigBadLou said:
Spiral, 30 to 40-degree bank angle. Speed +/- 5 kts.
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Not quite steep enough. The steeper you bank, the faster you come down. May have affected your comparison numbers. When I teach the spiral-down, full flaps, Vfe method, I'm looking for at least 45 degrees of bank. The rate of descent increases dramatically over the last 10 or 20 degrees. >2500 fpm down is not unusual in a 172 or 182.
 
The steep spiral and emergency descent are different maneuvers. Steep spiral is done at best glide.
 
RussR said:
Not quite steep enough. The steeper you bank, the faster you come down. May have affected your comparison numbers. When I teach the spiral-down, full flaps, Vfe method, I'm looking for at least 45 degrees of bank. The rate of descent increases dramatically over the last 10 or 20 degrees. >2500 fpm down is not unusual in a 172 or 182.
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Good point. The Private ACS says "use bank angle between 30 and 45 degrees to maintain positive load factors during the descent." The Airplane Flying Handbook says to do it when 'initiating' the descent. It doesn't go on to remind that steeper bank results in less vertical component of lift that will result in faster descent.
 
luvflyin said:
Good point. The Private ACS says "use bank angle between 30 and 45 degrees to maintain positive load factors during the descent." The Airplane Flying Handbook says to do it when 'initiating' the descent. It doesn't go on to remind that steeper bank results in less vertical component of lift that will result in faster descent.
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But as @dmspilot indicated, the expectation of the ACS still isn't a spiraling descent. The bank angle is only required to "maintain positive load factors" during the initial pitch down...in other words, get the nose down quickly without negative g's. Once the nose is down, the expectation is wings level or normal turns, as clearly indicated by the AFH.
 
I'm surprised that spins haven't been mentioned. Easy on the aircraft too. That's how the old air mail pilots got down through a cloud layer. I'm uncertain what the rate of descent is in a spin though.

Oh wait, spins...we don't teach that anymore...sigh.
 
saddletramp said:
I'm surprised that spins haven't been mentioned. Easy on the aircraft too. That's how the old air mail pilots got down through a cloud layer. I'm uncertain what the rate of descent is in a spin though.

Oh wait, spins...we don't teach that anymore...sigh.
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Spins are much slower.
 
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