Revisiting AADs activation speeds

[Deimian 43]

Reading some recent AADs threads an idea popped up. It looks like in some recent fatalities the AADs failed to cut the loop on time to save their owners after a cutaway. Possible contributing factors or concerns that people had mentioned:

-Stuffed containers
-Insufficient drag of the reserve PC.
-Slow opening reserves
-Disengaged or lack of RSL/MARD

The last one affects cutaway scenarios, whereas the others affect also total mals that require to use the reserve with the main still in its tray. In any case, discussions are been held to determine whether people should raise the activation altitude of their AADs.

So far so good. Now, what happens when the AAD activation altitude is high enough to allow the reserve to fully inflate and hopefully save somebody's life (an user that raised its activation altitude to compensate for some of the factors stated above), but the AAD won't activate after a cutaway because it has not reached the activation speed (i.e.: the jumper is in free fall but too slow for the AAD to activate during the first few seconds after a cutaway)? The resulting activation altitude will be lower, and potentially not high enough. The activation speed is the way that the AAD has to determine whether the jumper is in freefall or not.

What I am thinking to avoid this scenario (admittedly a corner case, but I think every fatality in this sport is close to a corner case, since in most of the cases any given skydive does not end up in a fatality), is to have some kind of built-in feedback device to notify the AAD that we are again in freefall even though we didn't build up enough speed yet. Something like a "freefall pin" that would be pulled similarly to an RSL, but whose only function is to tell the AAD that we are again in freefall after a cutaway. It can be just a cable to goes to a riser, and when the riser is released the circuit opens and the AAD knows that even though the activation speed is not too high, it will increase as we are in freefall, and therefore, if we are lower than the activation altitude it should cut the loop.

Does anybody know of a documented fatality or injury where the AAD cut the loop too late due to lack of speed? Or is this a solution to a problem that does not exist (or has not manifested itself)? I don't see any downside of the concept, but it might help to save a life or two, if somebody implements the concept in a practical and reliable manner.

This is meant as a discussion, so feel free to criticize the post. But please avoid posts like "the solution is to use better PC, non-stuffed containers or less cornered, fast opening reserves, RSL, MARDS, etc". I think all these things are a better solution, but they are not mutually exclusive of what I am saying. Besides that non-optimal PC and stuffed and cornered containers will be around for a while, not everyone agrees on using RSLs and MARDS, and the fastest opening in the world might not be enough if the loop is cut too late. Moreover these things have been discussed plenty of times in other threads.

[Top_Bunk 0]

Seems to me that this would be an electronic form of RSL, only with more failure points, no?

Instead of the main riser pulling the reserve pin, you're suggesting that the main riser pull a switch, which notifies an electronic control unit, which then fires a cutter, which then costs the user $250 for something an RSL would do more reliably.

Is the appeal related to the idea that it would only be active at a low altitude? For example, if someone refuses to use an RSL because he/she "wants to get stable before pulling the reserve" would this be an attractive option to that person?

Edit: I could see other possible applications for CRW jumpers, or others who have reasons for not using an RSL.

[Deimian 43]

Top_Bunk

Seems to me that this would be an electronic form of RSL, only with more failure points, no?

Instead of the main riser pulling the reserve pin, you're suggesting that the main riser pull a switch, which notifies an electronic control unit, which then fires a cutter, which then costs the user $250 for something an RSL would do more reliably.

Is the appeal related to the idea that it would only be active at a low altitude? For example, if someone refuses to use an RSL because he/she "wants to get stable before pulling the reserve" would this be an attractive option to that person?

Edit: I could see other possible applications for CRW jumpers, or others who have reasons for not using an RSL.

It is not an electronic RSL. If you see it like that I agree that it is totally stupid, as an RSL is a well proven device that it is unlikely to be outperformed by this concept. The point is that this is not an RSL. It won't pull the reserve pin on a cutaway. It won't prevent you from getting stable before opening the reserve. It will just avoid that the AAD cuts the loop too low. If the AAD takes the decision of cutting the loop then by no means you have altitude to get stable and pull the handle yourself. Its appeal is that it would speed up significantly the rearming procedure of the AAD after a cutaway.

I think the complexity of such thing would reside on making sure that when the device tells the AAD to rearm, it is not a false positive. On that sense, it indeed can add an additional failure point and cause the AAD to cut the loop without needing it, if the algorithms are not properly adapted or the device is not reliable enough. But this is a matter of implementation I think. It might be possible to implement this reliably, and it might be not, I don't know.

Indeed, I think CRW jumpers *might* be interested in this. At the same time CRW dogs are typically smart enough to don't get themselves to be that low without something functioning over their heads, as the majority of their problems happen up high. Also anybody else that do not want to use RSLs. The problem is that even if the concept makes sense, the market share (skydivers without RSL/MARD but with AAD) would be so small that no company would invest any money in R&D for this.

[airtwardo 6]

We were 'blue skying' some ideas like that around the bonfire a couple years ago...

One that kinda made sense though I have no idea how hard it would be to incorporate ~ have some kind of magnet or something at the far end of the cutaway cable...as the cable clears the housing it instantly either re arms or fires the AAD...if the rig is 'off the ground'.

And yeah...that 'would' be in essence a kind of electronic RSL.

~ If you choke a Smurf, what color does it turn? ~

[Deimian 43]

airtwardo

And yeah...that 'would' be in essence a kind of electronic RSL.

I still disagree with this . If you cutaway at 3000ft, but the activation altitude is a at 750ft, this thing would not trigger anything regarding deployment of the reserve PC, whereas any RSL, electronic or not, will do it. I just don't see the "static line" here anywhere. It would just rearm the AAD, it won't trigger any action regarding reserve deployment if the altitude requirement is not meet. An RSL does it regardless of the altitude, hence the "static line" in its name. If something I would call it electronic reserve dynamic line .

[Thijs 0]

Deimian

It would just rearm the AAD, it won't trigger any action regarding reserve deployment if the altitude requirement is not meet.

So how would the device then work? Say you cut away at 3000ft and not do anything. Then by the time you get to the activiation altitude, your speed should be higher then the activation speed.
But say you only cut away at just above 1000ft. Changes are that you won't have the activation speed. Should the AAD then fire at activation altitude, regardless of speed?
If so, won't that in case of a cutaway always result in a AAD fire? Or am I missing something? :)

[Deimian 43]

Thijs

*** It would just rearm the AAD, it won't trigger any action regarding reserve deployment if the altitude requirement is not meet.

So how would the device then work? Say you cut away at 3000ft and not do anything. Then by the time you get to the activiation altitude, your speed should be higher then the activation speed.
But say you only cut away at just above 1000ft. Changes are that you won't have the activation speed. Should the AAD then fire at activation altitude, regardless of speed?
If so, won't that in case of a cutaway always result in a AAD fire? Or am I missing something? :)

You are not missing anything. That is exactly what it is supposed to do. Cutting away at 1000ft you simply do not have time to get stable or anything like that. Under those circumstances you need to get something out as fast as possible, and that is the purpose of this thing. But it still allows you to get stable and pull manually if you have more altitude, contrarily to what an RSL does. In other words, it leaves you completely on your own unless it is completely necessary to take action. I still prefer a normal RSL, but there is some people that doesn't.

[wolfriverjoe 1,340]

Deimian

****** It would just rearm the AAD, it won't trigger any action regarding reserve deployment if the altitude requirement is not meet.

So how would the device then work? Say you cut away at 3000ft and not do anything. Then by the time you get to the activiation altitude, your speed should be higher then the activation speed.
But say you only cut away at just above 1000ft. Changes are that you won't have the activation speed. Should the AAD then fire at activation altitude, regardless of speed?
If so, won't that in case of a cutaway always result in a AAD fire? Or am I missing something? :)

You are not missing anything. That is exactly what it is supposed to do. Cutting away at 1000ft you simply do not have time to get stable or anything like that. Under those circumstances you need to get something out as fast as possible, and that is the purpose of this thing. But it still allows you to get stable and pull manually if you have more altitude, contrarily to what an RSL does. In other words, it leaves you completely on your own unless it is completely necessary to take action. I still prefer a normal RSL, but there is some people that doesn't.

I think you missed his question.

I read his question as:

Will the AAD still fire at ~750' after a cutaway, whether or not the reserve is open?

Scenario A - Cutaway at 900 feet. Your device arms the AAD and it fires, even though the jumper is not at freefall speeds.
This is it's intended purpose.

Scenario B - Cutaway at 3000 feet. Reserve handle pulled, under open reserve at 2000 feet. Flying under reserve canopy, what happens when you descend to and through AAD activation altitude?
Since your device has told the AAD to fire regardless of freefall speed after the cutaway, will the AAD fire as the jumper is passing (slowly) through ~750' under an open and functioning reserve?

I don't see any real advantages to this. It adds complexity, and does little that a normal RSL doesn't do. The failure modes for an RSL are rare enough (outside of special stuff like CRW and large camera setups) that I don't see this adding any advantages over an RSL.

And you asked if anyone had had a "cutaway too low to reach activation speeds" situation.

Yes.
The fatal in Eloy this month was one. She chopped low, didn't pull the reserve until too late. And she was too low/slow for the AAD to help. It fired after she pulled the reserve, but she had pulled the reserve low enough that it was barely out of the bag before impact. Brian Burke had a very detailed report in the thread in Incidents.
Billvon has stated that there were a couple of them just like that at the WFFC too.
So it has happened. More than once.

"There are NO situations which do not call for a French Maid outfit." Lucky McSwervy

"~ya don't GET old by being weak & stupid!" - Airtwardo

[Deimian 43]

wolfriverjoe

I think you missed his question.

I read his question as:

Will the AAD still fire at ~750' after a cutaway, whether or not the reserve is open?

Scenario A - Cutaway at 900 feet. Your device arms the AAD and it fires, even though the jumper is not at freefall speeds.
This is it's intended purpose.

Scenario B - Cutaway at 3000 feet. Reserve handle pulled, under open reserve at 2000 feet. Flying under reserve canopy, what happens when you descend to and through AAD activation altitude?
Since your device has told the AAD to fire regardless of freefall speed after the cutaway, will the AAD fire as the jumper is passing (slowly) through ~750' under an open and functioning reserve?

I don't see any real advantages to this. It adds complexity, and does little that a normal RSL doesn't do. The failure modes for an RSL are rare enough (outside of special stuff like CRW and large camera setups) that I don't see this adding any advantages over an RSL.

And you asked if anyone had had a "cutaway too low to reach activation speeds" situation.

Yes.
The fatal in Eloy this month was one. She chopped low, didn't pull the reserve until too late. And she was too low/slow for the AAD to help. It fired after she pulled the reserve, but she had pulled the reserve low enough that it was barely out of the bag before impact. Brian Burke had a very detailed report in the thread in Incidents.
Billvon has stated that there were a couple of them just like that at the WFFC too.
So it has happened. More than once.

Indeed, I missed the question.

Scenario B is not really relevant from the safety point of view (it is from the economic point of view though). You can change the algorithm to account for this case. Something like: If after a cutaway the fall speed did not increase passed a couple of seconds, or if it has slowed down, don't fire.

I agree that it adds complexity and adds little value over what an RSL does. I have an RSL and a MARD. With them this is pretty irrelevant. This concept/suggestion/discussion is for the people that don't want an RSL for whatever reason. For everyone else it is completely unnecessary.

I knew about those incidents, but I was too lazy to search the specific examples and details of them. I believe that in those cases this thing could have helped. Again, of course an RSL is better, but not everyone wants an RSL (I do!)