Figure 4-49. Riser release end.
Figure 4-50. Release housing and terminal.
Figure 4-51. A 3-ring release handle with yellow Lolon cable
needs oiling.
Figure 4-52. A 3-ring release handle with orange Teflon cable does
not need oiling.
• Main riser rings—check for webbing wear, hardware
plating, grommet wear, and locking loop wear/
damage. [Figure 4-49]
• Release housings—check for damage to terminal
endings and grommet, obstructions or dirt in housing,
and check security of the housing tacking to the
harness. [Figure 4-50]
• 3-ring release handle—check the cable for cleanliness
and cracks, and ensure that the cable ends are sealed.
Yellow Lolon cables must be oiled monthly to ensure
release-ability. [Figure 4-51] Red or orange Teflon
cables do not require oil but should still be inspected
every 180 days; inspect the Velcro ® on the handle.
[Figure 4-52]
Any questions concerning the particular harness 3-ring
installation should be directed to the harness and container
manufacturer.
Assembly of Components and
Compatibility
Advisory Circular (AC) 105-2D, Sport Parachuting states that
“the assembly or mating of approved parachute components
from different manufacturers may be made by a certificated,
appropriately rated parachute rigger in accordance with the
parachute manufacturer's instructions and without further
authorization by the manufacturer's or the FAA.” This allows
the rigger to assemble different canopies to different harness
and container systems. This is an important authorization for
any rigger in that there are dozens of possible combinations.
When various parachute components are interchanged, the
parachute rigger should follow the canopy manufacturer’s
instructions, as well as the parachute container manufacturer’s
instructions. However, the container manufacturer’s
instructions take precedence when there is a conflict between
the two. The logic behind this is that the container is the
active component and the canopy is the passive component
with regard to deployment. Determining compatibility is
more than simply determining the volume compatibility of
a canopy to a container size. Other factors, that need to be
considered are the deployment type, technical standard order
(TSO) certification, and placard limitations.
Reserve Bag Extraction Force
When we ask the question, “How do you determine
compatibility between approved parachute components,”
the answer is, “Rig functionality must not be compromised.”
Some say if a reserve canopy is too bulky, the reserve
deployment bag is not easily extracted. If you can get the
bagged canopy in the container, it should take no more than
18 pounds of pull force to extract it.
TSO Certification and Placard Limitations
This area is one where many riggers have some confusion.
According to AC 105-2, Sport Parachute Jumping, “the
strength of the harness must always be equal to or greater
than the maximum force generated by the canopy during
certification tests.” In the case where the harness is
certificated under TSO-C23b and the canopy under TSO-
C23c, the maximum generated force of the canopy must
not exceed the certificated category force of the harness
and container (i.e., Low Speed Category (3,000 pounds)
and Standard Category (5,000 pounds)). In this instance, no
additional marking on the container is necessary.
In the case where the canopy is certificated under TSO-C23b
and the harness under TSO-C23c, the strength of the harness
must be equal to or greater than the certificated category
force of the canopy.
For the current TSO-C23d, the peak force measured during
the strength drops must be placarded on the outside of the
harness. In this case, the strength of the canopy must not
exceed that of the harness.
The rigger, when making the determination as to whether a
particular canopy and rig combination is compatible, must
consider all of the above areas. If there is any doubt, the rigger
should contact the rig manufacturer for guidance.
Harness Strength
TSO-C23b was originally written back in the 1940s before
the advent of square parachutes. It had two categories under
which a parachute system could be certified. The “Low
Speed” category was limited to use in aircraft under 150 miles
per hour (MPH) and certified to 3,000 pounds. This category
required large block letters decrying “limited to use in aircraft
under 150 MPH.” It also had a “Standard Category.” This
category required no warning labels and had neither weight
nor speed limitations and was tested and certified to 5,000
pounds. It is important to note that neither category had a
weight limitation.
Weight has only a minimum effect on parachute opening
forces. To be exact, if you were to increase a given weight
by 50 percent, you would only see a 5 percent increase in
opening force; likewise if you double that given weight, you
would only see a 10 percent increase in opening force.
This seems counter intuitive until you think about it. Speed
is the critical factor that hurts us and our equipment when we
have the occasional hard opening. But because speed is often
derived from mass or weight, we associate the hard opening
with primarily weight. Let us look at the calculations.
The math model for opening forces is described in the
“Recovery Systems Design Guide” by Theodore Knacke.
The definitions and formula is as follows:
• Force—total opening forces
• C d—drag coefficient of canopy
• S o—square footage of canopy
• Q—dynamic pressure in pounds per/square foot
(½ ρʋ2)
• X1—decreasing load factor
NOTE: There are 2 methods for deriving this factor.
The Pflanze method and a lookup of the chart included
in the reference manual. The chart is the simplest for
personnel parachutes and effectively results in being
one tenth of the pound per square foot loading.
• C x = shock load coefficient which is derived from
testing and includes such things as slider size, brake
setting, angle of nose cut, etc. For this exercise we
will use a value of 1 as this number ranges from .5 to
1.5 or so. Without a slider it can go as high as 10.
Therefore: Force = Cd × So × Q × X1 × Cx
If we group the Cd × So × Q and calculate them, at first we
get a big number ie:
Cd = .8 S o = 200 square feet Q = 33 PSF @ 117MPH
together = .8 × 200 × 33 = 5,280 pounds. This number is
then ameliorated by the X1 decreasing load factor and the Cx
shock load factor. If the Cx is 1 (and we will assume this for
this example), then it has no effect on the outcome.
The X1 factor is the key because it is based on pounds per
square foot loading multiplied by 1. If you try different
weight values and reiterate the formula, you can see it only
Figure 4-53. Canopy characteristics.
Canopy Characteristics
Variable System 1 System 2 System 2
with 100-foot canopy
So
Subtotal
Force =
0.8
108.7
17,392
0.15
0.5
1,304.4
0.9
108.7
9,783
0.25
1.5
3,668.625
(Ratio 2.8125)
0.9
4,500
0.20
1.5
1,620 pounds
changes the X1 factor by fractional amounts and only affects
the outcome minimally as described earlier.
National Aerospace Standards (NAS) 804 has the best
requirements for structural integrity of any standard written
to date. This is because it has a strength requirement: 3,000
pounds for the Low Speed Category and 5,000 pounds for
the Standard Category. Other standards (AS8015) use a
performance requirement (weight versus speed) for structural
integrity verification. This would be acceptable except for one
small problem. AC 105-2, Sport Parachute Jumping, allows
for mixing and matching of approved components. This is
a problem because different canopies open with different
opening characteristics at the same weights and speeds. This
is defined and accounted for by the Cx value. Therefore, if a
harness is built and tested using a canopy with a low Cx and
matched with a canopy (under the provisions of AC 105-2)
with a high Cx, the results could be disastrous.
NAS 804 systems need no further consideration other than
originally called for. The Low Speed designation is limited to
use in aircraft under 150 MPH at any weight. Likewise, the
Standard Category of 5,000 pounds has no weight or speed
limitations. This is an unlimited category. One reason for this
is because of the limited effect of weight on opening forces.
Speed is what kills. If a human body were to reach a 5,000
pound shock load, it would come apart before the harness
or canopy. At less than 150 MPH, even at a high weight, it
will not exceed 3,000 pounds.
It may be evident now that there is a flaw in our structural
requirements due to the mixing and matching of approved
components under the performance standard versus a
structural standard. This came about as a result of the change
from a Structural Standard (NAS-804) to a Performance
Standard (AS 8015b). Now we have no way to determine
compatibility for TSO-C23c (AS8015b).
It may not be possible to have compatibility using
performance standards alone. That is why we added placards
for the “weight tested to” for harnesses and the “force
generated” for canopies to TSO-C23d. There is no way
to determine compatibility from one parachute system to
another within the same category of the same standard if
they are judged using a performance standard. Just because
they were tested at the same weight and speed does not mean
they saw the same opening forces. Different canopies open
with different characteristics. Listed below is a hypothetical
comparison of the opening characteristics of two different
systems tested to the same performance standard. The math
is the same as previously discussed. The two canopies have
very different opening characteristics, and they produce very
different results when tested at the same levels. When a mix
of the two systems is applied and subjected to a high-stress
sport jump, the capability of the harness may be exceeded.
Both systems were tested using a 300-pound test dummy at
180 knots (207 MPH) Cat “B” TSO-C23c.
System 1: 200 square foot canopy W/.8 Cd produces a 1,304
pounds force on opening at test speeds.
System 2: 100 square foot canopy W/.9 Cd produces a 3,668
pounds force on opening at test speeds.
The ratio of opening force differential is 2.8 to one or System
2 opens with 2.8 times greater force than System 1.
Let’s say a harness is built for System 1 using 1,500 pounds
capable hardware. It passes the structural drops, as it only
sees 1,304 pounds.
Another harness is built for System 2 that has a canopy with
desirable flight characteristics but that tends to open hard.
The jumper wants the canopy with desirable flight
characteristics in his new System 1 rig. If compatibility
is derived from performance standards, then these are
compatible since they were both tested using a 300-pound
drop test dummy at 180 knots. It is entirely possible that a
sport opening under extreme conditions could produce an
opening of 1,600 pounds, which exceeds the capability of
the 1,500 pound hardware. [Figure 4-53]
TSO-C23b does not really have any limitations except for
speeds below 150 for “Low Speed” category with no weight
limit. That standard is good for all skydiving scenarios. The
3,000 pounds test load is strong enough for anything and
force is a good base line for compatibility.
The current regulation for placarding (AS8015c/TSO C-23d)
calls for “Average Peak Force.” Under AS8015b/TSO-C23c
(the previous version), there is no way for a rigger to make the
necessary determinations without help from the manufacturer
Figure 4-54. Volume chamber.
Figure 4-55. Type 1 deployment in a pilot emergency rig.
doing some kind of retro placcarding as the requirement did
not include force measurement. Fortunately, there are only
a small number of systems/components certified under this
rendition. Any component so certified would not be able to
be used as there are no guidelines for compatibility.
Volume
An important criterion in determining compatibility is
the volume of the canopy. The canopy has to fit into the
container in such a manner as to not place undue stress on
the system when packing and to be extracted by the pilot
chute during deployment. The container manufacturer
usually provides a volume chart of their systems stating
what the volumes are for the various model sizes. Container
volumes are somewhat nonsequitur; however, as container
manufacturers derive their numbers in different ways. Some
container manufacturers do not publish numbers per se;
rather, they indicate a model designation that fits a size
range of canopies.
The canopy manufacturer should provide the volumes of
the canopy models. Measuring canopy volumes has proven
to be an imprecise science as there are various methods that
can be used. The most common method involves placing
the canopy in a tubular chamber and compressing it with
a standard amount of weight for a set time. The displaced
volume is then measured. Figure 4-54 shows one such
volume chamber. Slight differences in volume can be seen
from chamber to chamber and canopy to canopy. These
variances occur due to humidity at the time the test is
conducted and due to variation in the bulk of the fabric that
the canopy was built with. For example, sometimes a 150
square foot reserve is 312 cubic inch and sometimes that
very same model, built using a different dye lot of fabric is
363 cubic inch. Canopy volume charts can be found on the
Parachute Industry Association (PIA) website at www.pia.
com and the Parachute Labs website at www.jumpshack.
com. While some canopy manufacturers disagree with
the resultant numbers, most container manufacturers and
riggers agree that these independent test methods are useful
in determining volume compatibility.
Deployment Type
In Chapter 2 of this handbook, Design and Construction,
the different types of canopy deployment devices were
described. In some instances, the container system needs
to be of a specific configuration to accommodate a certain
deployment device. An example of this would be where a
round canopy utilizing a Type 1 configuration is packed into
a pilot emergency parachute system. In this case, the pilot
chute is compressed directly onto the floor of the container
system. [Figure 4-55] This same canopy can be packed into
a sport reserve container, but the sport rig has two internal
or staging flaps that compress and hold the canopy in place
and are locked together by the bridle. [Figure 4-56] The pilot
chute is then packed on top of the internal flaps. The rigger
needs to know and understand these differences to determine
how the two components interface for compatibility.
Figure 4-56. Type 1 deployment in a sport piggyback.
Chapter Summary
This chapter focuses on main parachute packing techniques.
The first rule is that the lines must be straight (no tangles,
also known as “step throughs”). If the lines are straight and
the slider is up (in square parachutes), the parachute will
most likely open. The speed of the opening directly impacts
the comfort or discomfort perceived by the jumper. Opening
speed and orderliness is controlled by attenuation devices
such as the slider, deployment bag, stow bands, or the diaper
on a round parachute. Accoutrements, such as pilot chutes
and bridles, must be checked frequently for wear that could
affect their performance.
Rubber bands should be changed when they begin to exhibit
small holes or ragged edges. Minor maintenance now
prevents hard openings and major failures later. Learn to be
observant of small details about the parachute system even
when packing the main. Virtually every pack job should
be an inspection. It does not have to be as thorough an
inspection as you would perform at the 180-day inspection
and recertification, but the packer should be vigilant for
damage or things that do not look quite right.
Compatibility can be complex. When in doubt about
which TSO a component was certified in, and whether it is
compatible with another component in terms of opening force
generated by the canopy versus strength of the harness, do
not hesitate to call the manufacturer for guidance.
One of the most critical things the rigger must observe when
servicing their customers rigs is reserve bag extraction force.
When a customer brings his or her container for inspection and
repack, reserve bag extraction force should be tested with the
container closed. A good rule of thumb is that the extraction
force should be the same as the weight of the bagged canopy.
If excessive forces are encountered, call the manufacturer.