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Revised Nov. 1999

Disclaimer

Given limited options as to an appropriate place to post this interesting article, I threw the following article into "Reserve Parachute Deployment and Repack Information." Though I am not sure I am happy with its placement here.

The study has left many unanswered questions... such as:

  1. is it human body oil that is degrading the material? (If so, cotton gloves may be in order.)
  2. is it the handling process itself (ie refolding, repacking) that degrades the porosity?

The real questions I would like to put to manufactorers are:

  1. Does this factor into paraglider porosity degredation? (Given the enormous number of times a paraglider is likely to be repacked.)
  2. Are some resin / color / sailcloth combinations more resistant to porosity degredation?
    (We are all aware that some colors of sailcloth degrade faster than others. Fleuro Pink being a classic example.)
  3. Is the material used in sport parachuting (ram airs and reserves) similar to that used in our sports?

If porosity degredation rates are similar in our reserve parachutes, this article provids a strong argument to encourage pilots who own one to two decade old reserves to purchase some of the new generation reserves which have come onto the market in the past few years.

Fred Wilson


CSPA submission to: Transport Canada ? CARAC
Chief Regulatory Affairs Secretariat
Effective 1 January 2000, the Canadian Sport Parachuting Association changed their Rules and Recommendations (PIM 1 ? 2.2) to read as follows:
"No parachutist shall jump unless wearing a reserve parachute which has been inspected and repacked within the previous 180 days by, or supervised by, a current CSPA "Type-Rated" or FAA "Certificated" Rigger.
Although there is a trend by military organisations to adopt a 12 month repack cycle for most of their parachute systems, the Technical & Safety Committee (T&SC) of the CSPA felt it was prudent to err to the conservative side as sport parachuting equipment is not necessarily under the same controlled environment as military equipment.
Numerous sport parachuting nations world-wide have adopted a 180 day repack cycle but the T&SC felt more extensive investigation of the results of this move were in order. During this investigation several nations, as well as the Parachute Industry Association and a number of parachute manufacturers, were contacted.
Following is a summary of some of the results of the move to a more lengthy repack cycle and recommendations from the industry.


Parachute Handling vs. Porosity

Barry McAuley log in for email link
Chair: CSPA Technical & Safety Committee Telefax: 1 604 939 8340
(Canadian Sport Parachute Association)

The Belgian Army Para School Testing:

The Belgian Army has conducted an extensive long-term study of parachute wear on systems used by the school. They were very interested in the effect of high altitude deployments possibly accelerating the performance degradation they were experiencing on their main canopies. From the first part of their study, they concluded that there was no direct relationship between the exact number and type of jumps and the degree of increase in porosity measured, though the porosity increase was great enough to effect performance. They also concluded that the handling during packing was much more detrimental to the parachute than the actual deployment and use.

This led the Belgian Army to question their beliefs about their reserve parachutes, "which we assume(d) stay brand new forever." In checking some reserves in their systems, they found porosity readings as high as 18 cfm in some areas of a parachute after only 30 repacks had been performed. A full 32% had porosity readings of more than 9cfm, with all parachutes tested having a porosity of at least 5 cfm in the center cell. The original mil specification, now a PIA specification, for the fabric used on this particular fabric requires 0-5 cfm when new. Among their conclusions was their standard practice of reusing a reserve canopy as a main without further checks had to be changed, and, "A reserve doesn’t stay a brand new canopy." They also concluded that the idea of, "having a check up after (a certain number of) repacks is not a bad idea." Note that the emphasis is on the number of repacks, not the period of elapsed time, because it is the handling during the repack that causes the wear.

Study by Precision Aerodynamics Inc. on Parachute handling vs. Porosity:

Precision, like most manufacturers, knows that all Ram Air parachutes built with conventional low porosity fabric are adversely affected by handling of the fabric. A study was recently accomplished where 10 different fabric samples were handled 16 times using methods typical of the packing of a parachute. Four samples were from a well-known company that no longer manufactures fabric, but is commonly seen in parachutes manufactured several years ago. The samples were in new condition and had minimal handling. The other six samples were representative of more modern 0-3 cfm fabric commonly used at this time.

Among Precision’s conclusions were:

After testing, the fabric had porosity increases ranging from approximately four-fold to slightly over twelve-fold compared to before testing. The fabric of newer design has generally better porosity characteristics, in that the fabric starts at lower porosity before handling, and does not degrade to as high a porosity as the fabric of older design. The porosity increases seen in these tests were representative of porosity increases seen on actual parachutes in service. The porosity increases seen on actual parachutes are due to the handling of the parachutes, mainly during the packing process. Parachutes that undergo such a porosity increase may not pass the TSO tests under which the parachute was originally certified.

Study by Performance Designs Inc. on actual opening and landing characteristics of reserve parachutes:

Performance Designs conducted a study of porosity of 18 reserve parachutes they manufactured between April 1990 and May of 1998. The parachutes ranged in size from 126 square feet to 218 square feet. After measuring the porosity on all the canopies, the company selected one large and one small parachute that had the highest porosity. These two parachutes were then packed and deployed from reserve containers after an intentional cutaway in the same manner as is done for TSO testing. The result was a noticeable increase in the time and distance required for both parachutes to open, and a very noticeable increase in the skill required to land the smaller parachute softly. The parachutes had been packed 10 and 14 times respectively, and both had only been deployed once before. While both parachutes performed reasonably well at this stage, considering the amount of handling they have had in that number of repacks, they are still far from the porosity level that they will attain after many more such pack jobs. Like any ram air manufactured using similar fabric, these parachutes may degrade to a condition where they may not pass TSO tests. They will certainly degrade to a point that the landing characteristics will not be acceptable to their owners or to the standards of the manufacturer, even if they do pass the TSO tests for landing performance.

Conclusions:

As shown by the supporting evidence above, it can be seen that there is no valid safety related justification for continuing with a 120-day repack cycle. There is however, a valid safety related reason for a longer repack cycle for ram air reserves. On parachutes made with very low porosity fabrics, most of the wear of the parachute canopy occurs during the packing procedure, rather than in the use (deployment) of the parachute. This wear can lead to a degradation of the parachute’s performance over series of repack cycles. In the case of ram air parachutes, this degradation may get to the point that the parachute may no longer be able to pass the original TSO tests used for the original certification. Specifically, the landing performance is compromised, as is the time and distance required to open. As the trend to smaller, more efficient ram air reserve parachutes continues, the ram air designs depend more and more on the improvements in porosity characteristics of the fabric they use. Lengthening the repack cycle will improve safety of ram air reserve parachutes. A corresponding safety related reason for a longer repack cycle on round reserves is that the porosity increase results in an increased rate of descent, however this was not studied extensively by the technical committee.

"The Parachute Industry Association supports the adoption of a world-wide standard 180-day repack cycle for civilian certificated parachutes."

Might frequent repacking adversely effect the airworthiness or performance of some parachutes systems?

In some cases, definitely yes. Parachutes made with very low porosity fabrics, (0-3 cfm permeability) do experience some degradation in performance due to an increase in porosity caused by handling the fabric during packing. In particular, for ram air parachutes, the change is quite noticeable, and can lead to the parachute eventually failing to meet TSO standards. For this reason, the Technical Committee is recommending that the repack cycle be extended to at least 180 days on ram air parachutes. Since the performance degradation is less severe on round canopies, the technical committee has not formed an opinion on extending the cycle for round canopies.

With few exceptions ram air reserves are made with a very low porosity fabric, for greater resistance to high speed tearing as well as great environmental stability. There is also a great deal of good experience with this type of fabric. Unfortunately, the trade off is an increase in porosity due to handling. By minimizing the frequency of repacking, the canopy’s porosity is maintained proportionally longer, resulting in greater safety for the user.
For these reasons, the CSPA technical committee suggests that the voting members of PIA support a change to a 180-day repack cycle.

Recent data from various canopy manufacturers indicates that modern parachute fabric may not be as hardy as previously thought. Parachutes made with very low porosity fabrics, (0 - 3cfm permeability) do experience some degradation in performance due to an increase in porosity caused by handling the fabric during repacking. In particular, for ram air parachutes, the change is quite noticeable, and can lead to the parachute eventually failing to meet TSO standards. Studies by both Precision Aerodynamics, Inc., makers of the Raven series of reserves, and Performance Designs, makers of PD reserves, indicate a degradation in canopy fabric which is elevated by the number of times handled during repacking.

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