Stall
 

I have a question. I am not a pilot and I kind of predicted as to what could have caused the plane to do what it did, but since I am not a pilot, or a mechanic, could you explain to me why the engines stalled? I can guess that the extreme drag could have through the whole thing out of whack, but I wouldn't have thought that the engines would shut down from it. Your going to laugh at me, but I can understand it in my head, I just can't put words to paper to explain it. lol. Could you please explain it to me so my conscious mind can understand it. :)

Certainly a severe aft weight load can explain running out of forward elevator authority as in your anecdote... while that weight is still onboard. But not after that weight jumps out.

And while it's certainly possible that a faster spooling engine on one side can induce a yaw and in turn a roll (and a spin given high AOA) it's hard to imagine (putting it lightly) one side spooling up faster, then the other side, then the first one again, then the other again, a 4-time reversal.

The pilot may have told his story, but I would not take it as the definitive recounting of the events, given 1) the high misunderstanding of flight dynamics that many pilots have, and 2) the potentially warped perception of a stressed and overwhelmed experience like this. This isn't an attempt to trash talk this particular pilot, it's just human nature. And if the pilot didn't realize what he was doing during the maneuver, his recollection after is very likely to be similarly flawed.

To more reliably build a picture of the events, we have to take in the video and circumstantial evidence. And the circumstance of someone who doesn't regularly practice spins, is that it's very common for muscle memory (aft elevator to move the nose up and out of the ground) to overwhelm any reasoned notion of the proper thing to do with the elevator. Including after a recovery. Add on the tunnel visioned stress of suddenly finding yourself in a spin in a large multiengine airplane not certified for this maneuver, I think the likelihood of an improper response only increases.

And what we see in the video after the first recovery and a sudden normal acceleration (to the right in the frame) consistent with high AOA. And after that, a series of roll reversals (some with yaw) immediately one after the other, with sudden pitchups in between... again consistent with high AOA, with the pilot doing their best to control the thing with rudder. Just like the "falling leaf" exercise in basic trainers where the plane is held in a stall.

I think Pilot DAR above may be on to something with the pilot overdoing an attempt to level off before the slick airplane accelerates past its airspeed limit (especially the flap speed limit), but in that case why would the power be advanced at all?

Jump pilots/sports parachutists reading this will be aware of Skies Call by Andy Keech - he captured the ultimate selfie of skydivers clambering all over a Lockheed 10E (Zephyr Hills?) Yes, it was a thing back in the Para- Commander days.

"could you explain to me why the engines stalled?
Engines throttled back as part of spin recovery? They didn't stall.

Hi Rich,

Stalling an aeroplane has nothing to do with the engines, you can stall an aeroplane with all engines at full power.

The word stall is used to describe the situation when the angle of attack of the air passing over the wings exceeds the maximum causing the airflow to break away from the wings and causing a sudden loss of lift. For many reasons this can then lead to a spin.

You can stall an aircraft at high speed, low speed, pointing straight up or straight down, full power or in a glider.

HTH

LD

Spin recovery 101
 

Sorry to play devils advocate here, but please look at some of the control positions and inputs when the aircraft should be RECOVERING from the spin.

In another, there are full pro-spin controls held during a supposed recovery, (reminds me of someone that tried to kill me in a Pa38)

I counted pro spin rudder, into spin aileron, and aft elevator in at least two of the videos ... do they not teach this stuff anymore ?

Sure, the aircraft is operating on the edge of the envelope, but if you are going to do that at least know how to recover if things go wrong.

I see right (anti-spin) rudder at all points where I can see the rudder in the first spin, as the subsequent ones it gets too small to see. I also can't see the ailerons at any point after the original entry.

edit: I see I think you were talking about the other videos, not the original one

Was that the infamous "Twin Spin?" I thought that was out in Cali somewhere, but that was a long time ago.

Knew Andy before he went to the US, last saw in Washington when he working in the Australian Embassy '67. Made a name for himself as a photographer in the jump scene.


https://cimg8.ibsrv.net/gimg/pprune....5beb3aedbe.jpg

North Carolina some where he says in an article, not Zephyr Hills.

Then look again, and watch the control inputs in the SE turboprop.
I am so disturbed with some of the videos I am not going through them again, but there are pro spin controls, aft elevator, and guys messing with the ailerons, all kinds of yeehaa stuff going on in some of them.

"Identify direction of spin, close throttle(s), full opposite rudder, ease the stick forward until the rotation stops, centralise rudder, recover from dive apply power as the nose reaches the horizon"

Mess with the ailerons, you are test flying unless it's a Pitts or similar.

Of course every dropzone & skydiving aircraft operator have their own procedures for handling jump run without stalling. What jump run speeds, what engine & flap settings, how many jumpers outside the door at one time, sometimes how many jumpers allowed aft of a red line on the floor at once, all those sorts of things.

But sometimes people and dropzones are still learning, procedures and skills are not perfect, and so on.

In the King Air event that started this thread, I notice that they were jumping from 16000' AGL according to the description. (At a DZ by the sea, so it should be about 16k' ASL too) That's an unusually high altitude, when typical turbine jump operations are from 12k to 14k at the most. I'm guessing the extra altitude was unusual, so right at the start of a special event going to that altitude, what worked down lower didn't quite work out any more. Little way of finding out without actually doing it.

So no kidding they adjusted procedures for the next load!

While I'm not necessarily that critical of the pilot for stalling it, I was less impressed with that long recovery process. Admittedly pilots don't exactly practice spinning King Airs a lot but there are procedures for inadvertent stalls or spins.

(I have 4k jumps. I was a jumper inside a Caravan during a jump run stall, but that was relatively mild, with the pilot not exceeding 60 degrees of bank on recovery.)

16 or 13K doesn’t really matter.

when I watched this clip for the first time I thought as well the recovery took quite some time. Having seen it a few times more and actually thought about it I think he did a good job. Spin recovery is easy when you expect it. I have at least 500 jump runs and never stalled. If it happened to me I hope I recover immediately but there is also the “startle and surprise” effect.

Looks like the pilot decided to join the skydiving party :)

Either way, some impressive footage there...

Well, he recovered didn't he? So, I guess must have done it right, all things considered...

Or is your issue more with the time it took for him to get it flying again?

Yes, as long as it was not over stressed or oversped during the recovery. Or. if it was, the pilot reported it. The 185 I used to fly jumpers in, was spun from jump run after I left that flying. The pilot landed, so I guess it worked, but they later found the the wings were wrinkled badly enough to write the plane off. A friend of mine bought it to rewing it. "Right", includes assuring that the next pilot, or maintenance person, is aware of any possible exceedances or defects resulting from what you did in it...

The Caravan is a turbine and is certified with a Vmo. It does not have a Vne. Although both speeds provide a margin to Vd they should not be confused because the Vne is literally the never exceed speed whereas Vmo/Mmo is a nominal limit approved to account for the inevitability of some speed excursions whilst operating there.

Looking at the way the control surfaces were deflected during first recovery attempts and knowing that twins are not spin tested/certified, I do understand unease when looking at this video. Two more turns due to ailerons still in spin inducing position and elevator solidly NU, I'm not sure he would still have been able to get it out of the spin. This might have been a very close call.

Yes, I stand corrected, it is presented as Vmo, rather than Vne for the Caravan. Though for either limiting speed, there is no authorization to exceed the speed within the certified limitations. For the flight testing I have done in Caravans the Vd agreed by the authority for the testing was 1.1 of Vmo, though there were discussions for a couple of projects that Vd might be a greater value than that. I've never flown the Caravan faster than 193 KIAS during testing. More simply, I'm saying that for the Caravan, and similarly sleek airplanes, it can be surprisingly easy to get to that limiting speed if you point the airplane down too much/too long! The Caravan is very forgiving in unusual attitude recovery, though a G meter is a good idea if you're going to do silly attitudes!

For all certified planes, the G (flight load factor limits) are presented as limitations, and the pilot of any airplane not equipped with a G meter has no way of knowing when the G limit is being approached.

You got a better idea? Ok, it is a turbine aircraft with good altitude performance, so maybe that's only a small difference in altitude, fair enough.
The pilot report stated, "The stall and subsequent spin happened when we allowed too many jumpers on the outside step, " ... but that doesn't say whether it was "more than usual" or just "too much for the given conditions".
Because it was a special event, maybe the number of people for that group was larger than usual or more focused than usual in keeping tightly packed near the doorway -- while at the same time perhaps the DZ's rules on the number of floaters wasn't that well established or perhaps communicated.

But it doesn't matter in the end too much here to us out on the internet. The drop zone would know "what factor changed", why a normal everyday jump run procedure didn't work this particular time.

Interesting. The 180 I used to fly had a VFR only guy get into a cumulus cloud on a fairly nice day resulting in a spiral dive and sharp enough pull-up to structurally damage it significantly. It seemed to look fine and I actually ended up jumping out of it that same day after it started flying again. The usual dropzone kind of stuff that seems to happen. And a good reminder that significant damage can be well hidden.