Tom Noonan is a professional instructor and director of the Tandem Program at UPT. Tom wears many hats on the side, including being the Dropzone Operations Coordinator at Everest Skydive, serving on the USPA Board of Directors, being a rigger and more! On occasion he even jumps for fun.
Flirting with AAD Activation Altitudes.
It’s that time of year again, where USPA dropzones around the country and around the world take a day off from skydiving to get recurrent on procedures and gear information. That’s right, it’s time again for Safety Day.
In last year’s BSM AAD article, we took a look at AADs in modern skydiving scenarios. We addressed the evolution of the “set it and forget” mentality associated with the use of AADs, and how in today’s modern multi-dimensional skydiving universe, how that philosophy might be outdated. From super fast freefall speeds of VFS to the super slow vertical descents of today’s modern wingsuits, we are seeing a broad spectrum of varied fall rates. We also learned that for all of these disciplines and fall rates, they each present a unique performance envelope that today’s modern AADs are expected to function within.
This information isn’t new, it’s something recognized by AAD manufacturers and skydivers the world over. The manufacturers have even gone on to create specialized AAD models and modes to account for all of these extreme performance envelops being reached (and in some cases, exceeded) in our sport. In addition to developing new models and modes for their AADs, the manufacturers went a step further, they also updated their manuals to explain exactly how these new advancements in design and technology would affect the end-user that chooses to jump with an AAD. That’s the good news. New features and products along with accompanying educational materials published in their respective manuals. The bad news however, is that despite these advancements and information dissemination, skydivers the world over, are still experiencing AAD activations through the normal course of their skydives without being in a “life saving” need of the unit to activate. Put simply, skydivers are placing their AAD units into the firing range category (approximately 78mph or faster at or below approximately 1100ft AGL) without being aware of doing so.
The primary question then is: “How can that happen?” If we know our gear and we know the parameters, how can we continue to place ourselves, and thus, our equipment in this danger zone of accidental AAD activations?
The answers are simples ones, but ones that deserves an in-depth look none the less.
The first answer is that many skydivers simply don’t know what the actual activation parameters are for their AAD. They have “an idea” of how high it will activate and at what speeds, but when pressed for specifics, many skydivers simply don’t know. Others may have a confident idea of these parameters, but when pressed with the most important three words in skydiving knowledge: “Are you sure?”, they recoil again in thought to rethink their answer. This generalized base of knowledge is the primary reason we still see AAD activations. Every skydiver has a general idea of the operating parameters of their AADs but some are still fuzzy on the specifics. Yet, the AAD is a precise, complex instrument, one that needs the end-user to be aware of it’s specific performance ranges, not just a general idea. The good news here is that it’s a simple fix. Just as we addressed last year, the most critical step in ensuring that skydivers understand the operating parameters of their AADs is to read the manual from cover to cover. Unfortunately, AAD manuals are similar to automotive manuals. They are delivered with the product, but rarely read until there is a problem.
The second answer regarding accidental AAD activations has to do with a fuzzy sight picture of altitudes against deployment sequences. Today’s visual altimeters can be classified in one of two categories: Analog (old school dial) or digital (can be numeric in read out or “new school” digital dial). While altimeters are an excellent representation of our approximate altitude above the ground, both versions: analog and digital, have a margin of error regarding what they read versus what the actual altitude is. There are many reasons for this, from barometric pressure changes to old internal components that need to be serviced, but the message here is simply that “2500ft isn’t always 2500ft from what you read to where you are.” The other fuzzy variable in this explanation is the deployment sequence itself. In almost every inadvertent AAD activation, the skydiver states that the deployment sequence started at a specific altitude and that they were sitting in at a specific altitude. “I pulled at 2500ft and I was sitting in at 1500ft” for example. The reality is when we see our altimeter read 2500ft and begin our deployment, we have only just started a process: first we (hopefully) wave off, then we reach back, grasp the pilot chute handle, and then begin the extraction of the pilot chute and then set it into the relative wind. Guess what though? That simple singular process burned up time and altitude before the deployment sequence even began. While 2500ft may represent to a jumper the “deployment altitude”, it is really just the initiation of a deployment. The wave off starts a process that takes about 3 seconds, and remember, based on an approximate 120mph freefall speed at deployment, we are falling at about 176 fps during this sequence. Based on time and speed, altitude loss can be as great as 500ft during the deployment initiation sequence, placing a jumper starting a deployment sequence at 2500ft at 2000ft by the time the bag is actually lifted off their back and deployment of the lines and canopy actually begins. (And remember from Answer One, we’re still only working in approximate altitudes here as nothing is exact in altitude readings on altimeters.) After the deployment sequence begins, we eventually reach line stretch of the canopy and are stood up during the remainder of the deployment and inflation of the canopy. What is not well know however is that this “saddling out” or standing up process actually causes us to accelerate before we decelerate as we have drastically reduced our surface area by assuming a vertical position during the latter half of the inflation. This speed variable is important because the AAD only needs to register a descent above 78mph in order to initiate an activation of the unit. And lastly, in terms of vertical descent speeds it is also important to understand that even after fully inflating, a canopy still needs a few more seconds to finish shedding it’s vertical speed as it assumes gliding directional movement. (For anyone that would doubt this, picture someone making a low turn and trying to stab the toggles and flare out of the turn, they stab flare the toggles, bringing the canopy directly over their head, but even with a fully inflated canopy straight over their head, they come down to the ground with a tremendous downward speed as they impact). And in the end, after this deployment sequence has completed, the jumper states they were sitting in at 1500ft when their AAD unit fired. Again, if we return to the margin of error on all modern analog and digital altimeters, it is not unreasonable to project a variance of a couple hundred feet, as the wrist altimeter and AAD pressure sensor are sitting in different burbles. Any and all of these factors can add up to a low deployment AAD activation that placed the operator into the activation parameters of the unit.
And lastly, it is not a surprise to anyone these days, that some of today’s modern main parachutes can easily achieve descent speeds above the activation parameter speed for most modern AADs. This is one of the most unfortunate scenarios to see continuing to occur, because it has been known for years that big turns under small parachutes can achieve activation parameter speeds, yet year after year, we continue to lose skydivers to this avoidable incident scenario.
In conclusion, if a skydiver chooses to skydive with an AAD onboard their harness container system, they must be vigilant in understanding the operating parameters within which they place the unit. The days of “set it and forget” are a thing of the past and skydivers in this modern three-dimensional universe of descent rate ranges must not just be familiar with the operating parameters of their AADs, they must be sure of them. “Are you sure?” Must be followed with a “yes”. Any answer to the contrary, the end-user is opening themselves up to the possibility of an inadvertent AAD activation. The good news is the information is easy to find. Every AAD manufacturer offers free downloadable PDF files of their manuals. (Look “here” to find a list of AAD manual links.) Someone famous somewhere said, “Those that cannot learn from history, are doomed to repeat it.”
AAD activations, whether live life saves or inadvertent activations, are thankfully not a common event either way. That said, we can all do our best to ensure we do not find ourselves repeating an accidental AAD activation by arming not just our AADs, but our minds with the necessary information we need to be sure that we are operating our skydiving equipment in accordance to operating parameters of all of our gear, including our AADs. To do any less is to open ourselves up to dangers that we already know are out there. Be Vigilant. Be Safe. Be Sure.
And remember, every day should be safety day.
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