Emergency parachutes for free flight do really work. Since 1977, when Jim Handbury had the idea of attaching an emergency parachute to a hang glider and it’s pilot, thousands of pilots’ lives have been saved.
The
important thing about parachutes is to have one when you need one.
The second most important thing is that it
works when you need it to.
In France, especially among paragliders, a large number of pilots still do not fly with a parachute. Rather than make it mandatory to fly with a parachute (which is quite useless because it’s almost impossible to enforce), it’s more important to change the outlook of pilots. Instructors should institute the use of helmet and back protection from the very first practice sessions at the training hill, and use of a parachute as of the first flight. This way, new pilots learn to regard these items of safety equipment as indispensable, and those who fly without, instead of being seen as ‘cool’, should come to be regarded as poor fools.
There is much discussion about emergency parachutes, and for those who are not professional in the field, it is very difficult to sort out the claims forwarded by the ‘experts’. Since we speak here of a critical safety issue, it is necessary for all questions to be given a satisfactory answer. Instead of just giving my own solutions to the various problems surrounding use of emergency parachutes, I think it best to provide an overview of all points so that each pilot can formulate his or her own thoughts and judgement.
Much as I have made every effort to remain objective, this article is the synthesis of thoughts I have formulated in my 20 years of experience in this field. At any rate, I have tried to emphasise the problems rather than highlight my own solutions to them. Other experts may not necessarily agree on certain points; this only highlights the fact that an emergency parachute is the resulting compromise of solutions to performance requirements, which frequently oppose one another. This is the source of the different theories since not everyone will agree which factors are more or less important than another.
"Reliability", in its general sense, is surely the most fundamental characteristic of an emergency parachute: it’s almost useless to have a parachute if there is little chance that it will work properly. Every emergency system must be quite simple to be able to function properly all the time and, preferably, not giving the pilot the opportunity to make a mistake in its use. This may seem obvious, but in reality it’s quite difficult to achieve a high degree of reliability because a parachute is often installed in a harness which was not specifically designed for it and use of an emergency parachute occurs in a complex environment with many, ever-changing, variables. A special care must be taken to consider any possible complications.
Murphy’s Law says: "anything that can go wrong, soon or later will go wrong". This isn’t a pessimist’s outlook by any means; it’s simply logic and is the way it is in real parachute deployments.
I have seen many cases where the parachute was rendered completely useless solely
because of small, seemingly insignificant details: release pins that were too long, hook
Velcro sticking to parachute lines, deployment handles too difficult to grab in a spin,
apparently minor mistakes in repacking, etc… Actually, one can say that the degree of
reliability of a parachute is the balanced sum of all its characteristics. The
"perfect parachute" should provide (in order of discussion):
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Let’s analyse each of the key points one by one:
Reasonable price: That’s the natural request: ‘the less it costs the happier I am", especially since it’s something I have to have, but will never use (at least that’s what I hope!). In reality, even price is a safety factor, because if the price is too high, more pilots will decide to do without. The bottom line is that the biggest mistake you can make is to fly without a parachute because any parachute is better than none at all.
Minimum weight and encumbrance: At first sight this doesn’t seem so much important, but these attributes allow a parachute to deploy more rapidly, make it easier to throw and easier to mount on a harness such that it won’t impede the pilot’s movements. Also, heavier equipment contributes to fatigue and encumbrance at launch, which is certainly a significant safety consideration. If safety equipment provides minimal encumbrance there is a greater chance that a pilot will always carry it along, even if they think they’ll never use it.
Ease of mounting: Many times impressive contortions are required to stow a good parachute in a good harness with acceptable results. This is quite a serious problem, which really demands standardisation of systems between parachute and harness manufacturers. First and most importantly will be to decide whether the deployment handle and the bridle are part of the parachute, or part of the paragliding harness.
No risk of accidental deployment: Unintentional deployments are too frequent, and in my opinion, it is unacceptable to have safety equipment which can cause problems during a routine flight. Deployment handles which protrude too far, Velcro, solitary deployment pins, or pins that are too short, and four-flap style containers can cause accidental deployments. The container must be designed to minimise the possibility of accidental deployment; prior to every flight the pilot must verify the parachute is securely stowed.
Easy extraction: It must be easy to remove the parachute from its
harness-mounted container, that’s obvious, but this once again poses a serious
problem in compatibility between harness and parachute. The shape of the deployment handle
is very important: it should be semi-rigid and easy to hook a thumb through to guarantee a
secure grasp when needed. It often happens that the parachute is too difficult, or even
impossible, to extract from it’s container (especially for less aggressive persons)
because of too much Velcro, or deployment pins which are too long. In certain cases, if
the pilot’s in a spin, it’s not even realistic to grab the handle of many
parachute systems. After having mounted a parachute on a harness, it’s vital to do a
hang check to verify that the deployment handle is truly easy to grab and that the
parachute can be pulled from the container with minimal effort and in any variety of
pilots position and circumstances. Seems obvious, but almost no one actually does it! The
positioning of the parachute system in paragliding, the shape of the deployment handle and the length
of its connecting strap to its pod are very important.
Ventral position: often one must attach the
parachute before each flight. The handle is highly visible and reachable with both hands
when one is seated upright, but it blocks the view and the handle becomes almost
impossible to grab during a spin when the harness has been adjusted for a partially
reclined flying position.
A pod which will not open before the right time: Once the pod is extracted from the container it is fundamental it does not open until the parachute has actually been thrown. If the pod opens before this time there is a much greater chance for the parachute to hook on something causing malfunction. The pilot must be able to wait, pod in hand, for the right moment to throw.
Ease of throw: This is a very important factor depending on the weight and encumbrance of the parachute, but above all, on harness/container geometry, and the position, orientation and shape of the deployment handle. If the strap connecting the handle to the pod is too long, or if it’s attached to the pod at a single point, it becomes very difficult to control the throw and the parachute may snag the hang glider frame or, even more likely, wrap itself among the paraglider lines. Double handles, which have been relatively popular in recent years, are especially prone to tangle in paraglider lines impeding parachute deployment. Hook Velcro, found on many deployment handles, can be responsible for a variety of deployment problems and has been the cause of at least one death.
Ballistic and pneumatic systems have been used to assist deployment. The advantage of these systems is that they allow optimal positioning of the deployment handle and bring the parachute to full line extension very quickly. The disadvantages are that it is impossible to choose the direction of deployment, and system complexity is significantly greater which reduces reliability.
Choice of correct throw direction contributes to a more rapid deployment and helps avoid a host of serious problems which may lead to malfunction - it is vital that pilots learn to follow the correct deployment procedure.
Correct deployment sequence: To reduce the possibility of malfunction during deployment of the parachute, and to reduce the risk of interference with the hang glider or paraglider, one must guarantee that the deployment sequence will be ‘bridle - lines - canopy’ and that the pod will not open until it has been thrown. If the pilot has not succeeded in an aggressive throw and one falls at more or less the same speed as the closed pod, it becomes indispensable that the pod will open with very little line tension.
The cumulative length of the bridle, the lines, and the parachute canopy must be less than the line lengths of the paraglider. If this is not the case, the parachute may interfere with the leading edge of the paraglider, impeding, or at least delaying, full deployment. This penalises parachutes with a larger surface area since, generally speaking, a parachute’s sink-rate and stability suffer badly when the length of the parachute lines become less than the diameter of the canopy.
For hang gliders, to keep the parachute away from the wing, the bridle must extend past the hang glider’s leading edge. But paradoxically, much as it is required that the bridle is long and that longer lines improve stability and parachute sink-rate, it is necessary to have a short sum of bridle plus lines to get a fast deployment; Is a compromise necesssary?
Guaranteed opening: It must never be forgotten that anything attached to an emergency parachute is something that can snag. As such, the pod must never be attached to the parachute canopy, and pilot chutes must never be used regardless of configuration. For the same reason, canopy vents increase the possibility of fouling during the deployment sequence. In a real life emergency, it is shown that one falls at relatively low speed, and the pod, still closed, falls faster than the pilot. It is precisely this difference in speed that extends the emergency parachute lines facilitating its ultimate deployment from the pod. Any factor slowing the fall of the pod in this scenario leads to delayed deployment.
Once line and canopy extension occur, and nothing has snagged, the possibility that a round parachute will not open correctly is negligible. One cannot say the same of more complex parachutes, those with vents, those that are steerable or asymmetrically vented, and especially those parachutes of the Rogallo style which are highly susceptible to even the smallest mistake in packing or interference during the deployment sequence.
Rapid opening: In the mountains the majority of one’s flight time is spent relatively close to terrain, exactly where the possibility of tumbling and collapses are the highest. Furthermore, in case of a collapse at high elevation above the ground (without structural failure), a paraglider pilot must always focus on regaining control of his wing, avoiding use of an emergency parachute unless all else fails or little elevation remains. In real accidents one drops at relatively low speeds, often less than 10 m/s, because the broken hang glider or collapsed paraglider greatly slow the descent. Rapid deployment of an emergency parachute is indispensable especially for these low speeds.
Everybody always speaks of ‘opening speed’, but in reality it is the ‘vertical opening distance’ which counts, i.e. the vertical distance necessary for the parachute to open. This opening distance largely depends on your sink-rate at time of deployment: a lower sink-rate usually requires a greater opening distance. The most difficult situation for deployment is the negative spin (no forward speed and low vertical speed), whereas, for example, a spiral dive autorotation (high speed) speeds up parachute deployment. The bottom line is that the parachute must open correctly at any speed. Note that if the parachute opening tests are made starting from 0 speed, with the pod attached, the opening distance is shown to be almost precisely a function of the opening time squared, i.e. doubling the opening time requires basically 4x the opening distance.
High structural integrity: A parachute designed specifically to withstand the opening shock associated with terminal velocity is no doubt desirable but, to reduce the opening shock to an acceptably safe level for the pilot, it is necessary to increase the opening time, which increases the vertical opening distance. This is not at all desirable for free flight application.
Years of accumulated experience suggest the choice of the following compromise: set structural standards for paraglider lines and hang glider hang-loops high enough to essentially exclude the pilot can separate from his paraglider or hang glider, and test emergency parachute equipment for structural integrity to roughly 150 km/h. Remember it takes considerable time and distance to reach high speed: if terminal velocity is 180 km/h (chosen value by skydivers), it takes 6.1 seconds (151 m) to reach 150 km/h in free fall, while to reach 170 km/h takes 9.1 seconds (283 m). It is wrong to say that ACPUL tests parachutes in free fall and DHV does not: for paragliders, ACPUL makes one test dropping an 80 kg weight for 5 seconds (ignoring friction, reaching a maximum of 176 km/h) while DHV drops a minimum weight of 100 kg from 85 m (providing a top velocity of 147 km/h). The ACPUL tests load the parachutes with 14% more energy, but DHV makes the test three times with the same parachute, in which process the parachute lines lose elasticity - we leave it to you to judge which test is more severe.
To provide perspective, the American TSO certification for sky diving and military parachutes require the same parachute to be submitted to 60-odd deployments with a 77 kg load, frequently at 240 km/h (double the energy roughly of the European free-flight certifications). The European CEN certification for emergency parachutes has not yet been officially completed and as such I provide no comment on these new standards.
Small opening shock: This is a continuation of the same issue as structural integrity: reduction of opening shock is inextricably linked to an increase in opening distance. It is worth remembering that a pilot can withstand an opening shock of well over 20G since he is subjected to this force for only a very short time. Also worth remembering is that the opening shock is proportional to the velocity squared: for example, giving the same parachute, the opening shock at 150 km/h is 9 times greater than the opening shock at 50 km/h.
Lack of oscillation: A high level of stability is vital since the ultimate impact force when a pilot touches down often depends more on the pilot’s swinging to and from than on the actual sink-rate of the parachute. In this context one must take note that,generally speaking, high porosity fabric makes for a more stable parachute and a lower opening shock, but does this directly at the cost of sink-rate and opening distance. The best results are certainly achieved by designing a parachute specifically for the intended application. A common misconception is that classic style round parachutes are more stable and oscillate less than pull down apex ones. Stability is often influenced by seemingly insignificant factors and is always heavily influenced by the close proximity of the malfunctioning paraglider and by the exact position of the center of gravity of the pilot with respect to the emergency parachute canopy. This center of gravity position is mainly determined by the location of bridle attachment points on the harness and the bridle geometry.
Low sink-rate: It is possible to improve (i.e. reduce) the sink-rate for a parachute of a given size by designing it with the highest possible aerodynamic drag coefficient. However, to obtain a better sink-rate for the same pilot weight on the same model parachute, the only possibility is to use a larger size parachute. A seemingly obvious choice made by many, however, a larger size requires a greater opening distance, more weight, more volume, greater encumbrance to extract from the container and accurately throw, and a higher price. A larger size of the same design has longer lines and requires a larger volume of air for inflation: at high speed the vertical opening distance required by a parachute is related to the square root of the surface area (doubling the surface area increases 1.41 times the opening distance). However, in real life deployments at very low speed, other factors, especially the parachute weight, strongly influence this formula: a reasonable estimate would be that a parachute of the same model, but twice the surface area will require almost twice the opening distance.
It is difficult to visualize a sink-rate given in m/s. A good system to gain a feeling for sink-rate is to use ‘equivalent jump height’ instead of sink-rate. Since friction of the falling pilot can be assumed to be negligible, the kinetic energy (mv2/2) equals the potential energy (mgh): this provides us an equivalent jump height of h=v2/2G. For example, a sink-rate of 6 m/s is roughly equivalent to jumping from a wall of 1.8 m height (6 x 6/20). If one knows the equivalent jump height of a parachute model with a particular pilot weight, it is very easy to calculate the equivalent jump height with your own weight. The relationship is, for our purposes, directly proportional, i.e. double the pilot weight gives double the equivalent jump height which gives double the energy of impact. It's easy to simulate the landing impact by hanging yourself in your harness from a cord passed through the same anchor points that your parachute bridles are attached to, with your feet at the equivalent jump height corresponding to your weight, then cutting the cord. Don’t do this test if you have any doubt concern at all of hurting yourself and don’t place too much confidence in back protection: rigid style back protectors can allow expose your spine to an impact force of 40 G in a fall of only 30 cm - more than enough to collapse vertebrae and put you in a wheelchair for life! The greater the sink-rate the greater the risk of injury. However, the more we reduce the sink-rate the longer it takes for the parachute to open and then we must concern ourselves that the parachute may not open in time during a low elevation deployment. A lower sink-rate makes it easier to disable the paraglider to reduce its interference with the parachute; however, this procedure requires altitude and experience to be successful. It should be the responsibility of instructors to teach newcomers to our sport the correct procedures for disabling the paraglider and how to properly execute a PLF (Parachute Landing Fall), which is not only useful during a parachute landing.
The controversy over sink-rate is essentially a philosophical problem: Alain Zoller - Swiss Federation test pilot - with considerable experience deploying parachutes in simulated accidents, prefers a good sink-rate, while Andy Hediger - renowned Paratech test pilot - who has performed at least 5 deployments in real accidents, prefers flying with a parachute which opens fast. To allow everyone to decide for themselves, pilots must be clearly informed what sink-rate they will get with their weight on a particular make and model of parachute, very carefully remembering that what is acceptable for a young karate champion would be totally inappropriate for an elderly pilot in average physical condition.
These are the maximum sink-rates allowed by the different certification organisations. To easily compare them I have listed the equivalent jump heights for 60, 80 and 100 kg pilot loads.
60kg |
80kg |
100kg |
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DHV: 6,8 m/s at 70 kg |
2.02 |
2.69 |
3.36 |
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ACPUL: 5,5 m/s at 80 kg |
1.15 |
1.54 |
1.92 |
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TSO: 6,4 m/s at 77 kg |
1.63 |
2.17 |
2.71 |
The DHV and ACPUL values are specifically for parachutes intended for emergency use for free flight. The TSO values are for military parachutes and emergency parachutes for skydivers. I have added the TSO standards for comparison and because it’s the certification which has been most heavily tested and is universally accepted.
At first glance it seems that DHV accepts very high sink-rates, but it is important to consider we’re speaking of maximum values here: as for DHV, a very heavy pilot would purchase a larger parachute, certified for a higher weight. With the ACPUL certification, even if one is very light, he cannot purchase a smaller parachute to reduce weight and encumbrance because the smaller size cannot be certified. Sink-rate changes dramatically with pilot weight and it is not possible to have one parachute for all pilots. In this regard I have long proposed to CEN (the new European Certification Standard) that all parachutes should have a label with a number which, when multiplied with the weight of the pilot, gives the equivalent jump height. As such, everyone would be able to choose an appropriate size parachute and be aware of the results and requirements of one’s choice. The impact force at the ground heavily depends on wind speed: roughly speaking, a 20 km/h breeze would result in double the impact force as one would experience in calm conditions, and a wind speed of 40 km/h would result in a impact of 5 times larger than calm conditions almost regardless of the sink-rate of the particular model emergency parachute.
DHV and ACPUL differ considerably also when it comes to their choice of acceptable parachute opening times: their respective tests do not resemble one another in any way and, as such, are extremely difficult to compare. However, in broad strokes, ACPUL requires an opening time of under 4 seconds in a rapid autorotation and under 6 seconds in a parachutal phase. DHV requires the parachute to open in less than 60 vertical meters when the load (simulating the pilot) and the parachute are dropped in free fall, side by side, at the same time.
Steerability: The ability to steer a parachute away from an obstacle, or to face oneself into the wind, would be an evident advantage. For hanggliders this is not possible because the long bridle removes any possibility of use of a directional control mechanism. For paragliders it is possible to use round steerable parachutes, providing a glide of less than 1 if the paraglider is released. With the paraglider there is a huge loss in glide performances and, with sufficient altitude, it is probably possible to get oneself facing into the wind.
A Rogallo style emergency parachute is a different matter: deployment is rapid and it has a glide angle close to 3:1, but to avoid serious problems of interference between the two ‘wings’ it becomes necessary to cut away from the paraglider. This involves, of course, a serious risk of entanglement and a remarkable complexity in procedure, especially if one takes into account other details such as disconnection of the speed system. In my opinion, given the likelihood of deployment at lower elevations, the real benefits are minimal compared to the theoretical benefits and are possibly overshadowed by the system’s disadvantages.
Geometry facilitating PLF (Parachute Landing Fall): Certainly one of the most important issues. However this depends on the location of the attachment points of the parachute on the harness, and not on the parachute itself. Our legs are very efficient shock absorbers: a fall of only 50 cm on the back, without suitable back protection, can easily put us in a wheelchair, while such a fall landing on one’s feet is absolutely insignificant. Suspend yourself with your harness, 2 meters above the ground from a variety of anchor points corresponding to possible attachment locations for your emergency parachute bridles, and imagine cutting the rope and performing a PLF from this height. The best points of attachment for the parachute bridle are the specifically intended shoulder location common on most paragliding harnesses. Use steel quick-links instead of knots or girth hitches, which can cause the webbing of the bridle to melt through under high impact loads. There are two bridle styles to attach the parachute to the harness: inverted V, and H. If the inverted V bridle is too short the pilot could have problems with his neck. Conversely, since the shoulders are not likely to be at the same height at the time of the opening shock, use of an H bridle can result in the parachute opening into a ‘Mae West’ malfunction. Both cases offer drawbacks, however they are extremely improbable.
For hang gliders, it’s best to anchor the parachute bridle directly to the main harness carabiner so that during the descent under parachute, the parachute supports the weight of the glider and the pilot will have some possibility of movement. If the parachute is attached to the pilot, the opposing aerodynamic forces of parachute and glider will trap the pilot in a likely undesirable position and, as unfortunately happened to Brad Koji, the bridle or control bar can hook under the pilot’s chin. Watch for harnesses with large stiffeners in the back: can prevent your back from bending to absorb shock upon landing, thus leading the possibility of crushed vertebrae.
Ease of repack: Ease of repack is a fundamental characteristic of an emergency parachute as is its capacity to function even if it has not been perfectly packed. The layout must be such to preclude the possibility of significant packing errors. It is vital to provide good packing instructions with the parachute and that no one with inadequate experience shoulders the responsibility of parachute repacking. Rogallo style parachutes must in all circumstances be packed by true experts.
Ease of maintenance: Maintenance, and especially timely repacks, must be easy to perform and be well-explained in a comprehensive owner’s manual precluding chance of error. Packing a parachute every 3 or 4 months facilitates faster deployment and provides the best way to do a safety check on the system so that one is always confident it will work when needed. When buying a parachute do not discount the possibility that lines and/or bridle may be easily replaced.
Long life span: Parachutes are constructed of synthetic materials which, while of impressive strength, deteriorate over time. The canopy nylon is very susceptible to UV radiation: left in the sun, the canopy can lose up to half of its strength in one week and, as such, must be effectively protected. Take note that many weaves of container material allow light (and hence UV) to filter through to the parachute. Regardless, it is best to retire a parachute after 10 years, or use it only as secondary parachute.
Guaranteed specifications: A parachute’s specifications must be printed on the canopy to allow a pilot to verify its suitability. These specifications must be guaranteed by the reliability of the manufacturer, or better yet, by a certification system which is both serious and comprehensive of everything which, in my opinion, does not yet exist.
Personal Thinking
Having provided this review, I leave it to the individual to carefully weigh the information, and upon final evaluation, decide the best compromise for oneself.
One might think that I have written much of the above to justify certain choices I have already made. Others would think that the above reflections have naturally led me to the parachute which I have designed providing the best compromise in my opinion. Everyone can think what they will, but I wish to here explain the reasons for my personal choices.
There is a profound difference between tests performed for certification, tests performed for demonstrative purposes and real life emergency parachute deployments. In the first case one wishes to verify that the parachute falls within parameters established more or less arbitrarily by some individual or organisation. In the second case one wishes to demonstrate that the parachute works well and brings you softly to the ground. In the third case one wishes to save one’s life. In my opinion, an emergency parachute is used when one’s life is in the balance and, as such, must offer the greatest probability to perform properly in the scenarios which have been shown to be the most common, the most important of which is low altitude above ground.
In the owner’s manual of all my parachutes I provide the formula to calculate sink-rate using your own personal body weight (of course this formula is not applicable to other parachutes): the equivalent jump height which I advise whether using a CONAR or CLASSIC model is between 1.3 and 1.7 meters with an absolute maximum of 2.1 meters.
Until now (December '99), there have been 220 confirmed deployments of my parachutes in real life accidents, and probably many others I have not been made aware of. With the exception of minor scratches, in these accidents a total of six pilots were injured:
A German pilot died at Castelluccio di Norcia, in Italy, because he added a deployment handle extension with "hook" Velcro to the existing deployment handle, which blocked opening of the pod.
Of these 220 deployments, roughly half were made below 100 m AGL, and a quarter below 50 m. We encountered two cases of free fall (both of them with the Classic model): at Laragne, in France, Derek Austin broke the keel of his hang glider and unfortunately was not able to throw his parachute before reaching very high speed; when he finally did deploy his parachute, the lines separated leading to his death. Andy Hediger in Zillertal, Austria, after all lines of his prototype paraglider broke, threw his parachute at a speed which was probably much higher than the 138 km/h measured by his barograph (recording data in 4 second intervals). He landed safely after a descent of more than 2000 vertical meters with an average sink-rate of 5.5 m/s.
Derek was the president of the safety commission of the British Association: he was my friend and in a sense I feel responsible for his death. If I had chosen a different compromise, perhaps he would still be with us. But then again, what would have become of the Karl Reicheggers, Robbie Whittals, Andrea Patruccos and others who threw their parachute less than 30 meters from the ground and the parachute opened just in time to save them?
Several years ago, the British Association compiled a general accident statistics showing that when an emergency parachute functioned correctly, it saved a pilot’s life in 97% of deployments. In the remaining 3% were included cases where the parachute did not deploy properly or quickly enough, and further included a solitary case where the pilot died of the speed at impact under canopy.
This proves emergency parachutes in free flight do indeed work; there is always the possibility of improvement (a 3% failure is quite high anyway) and the developmental process must continue. Nonetheless, I believe the most useful step to take involves convincing all pilots that the parachute is not an accessory, but an indispensable piece of equipment and one must learn how to use it.
Even though an emergency parachute cannot provide a 100% guarantee, and as such should be seen not as a guarantee but as another possibility, one must never forget:
Written by Angelo Crapanzano — metamorfosi
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