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Recently I had the opportunity to take a closer look at the skydiving parachute. And I could not explain to my self the reason to use D-Bag and not pack main canopy directly in backpack compartment. I know that the reserve canopy is packed directly into the backpack. And the sequence for deploying reserve canopy is:

  1. Sky diver pulls release cord, which pulls out the pin that holds the backpack flaps close
  2. Spring loaded drogue parachute jumps out into the airstream
  3. Drogue chute pulls out the main canopy which opens
  4. Sky diver does not flatten him or herself on the ground.

More puzzling is the main canopy assembly. As far as I could understand the main canopy is packed into so called D-Bag. This D-Bag is then inserted into container in the main backpack. Why this intermediate step? The deployment sequence of main canopy is described here: http://adventure.howstuffworks.com/skydiving4.htm

I wonder what happens to the D-Bag after deployment. Does it hang loose? Does it remain close to the canopy on the upper side? As far as I understand the drogue chute remains attached on the back side of the canopy and acts as a sort of stabilizer. But what about D-Bag? Does it just flap around? Why not pack main canopy in separate compartment of backpack directly?

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Qualifier: I am a master parachute rigger.

The bag serves two functions - it allows the suspension lines to straighten out in a controlled manner, and it prevents the canopy from inflating before the lines are fully stretched out.

It is not always required - people who want a very fast opening can pack without a bag, I have done this many times myself. However, you do NOT want to do this after a drop of more than about 5 seconds. These jumpers open the main canopy immediately after exiting the aircraft.

On main canopies the bag and pilot chute are connected to a ring on the top of the canopy. The assembly just follows behind. Some canopies have a mechanism to collapse the pilot chute and/or retract it onto the top of the canopy.

The bag for the reserve canopy is not connected. This allows the reserve to still deploy if the pilot chute gets caught on something else, the bridle is extra long (longer than the suspension lines). It falls separately and usually lands within a kilometer of the airport, near the main canopy if that one was released when it malfunctioned. As they cost about $200 a set the jumpers will put considerable effort into finding it. We usually don't find it in high crops, and we usually don't try to find it at some places in Florida where there is an alligator ranch beside the airport.

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    $\begingroup$ As a master parachute rigger, I'm sure your answer is 100% spot on. As someone who questions the sanity of leaving a perfectly functional aircraft while it's in the air, would you mind updating your answer with a picture that shows all the different bits you're talking about, or include some links to those items? It would make a great answer excellent! $\endgroup$
    – FreeMan
    Commented Jun 15, 2015 at 16:42
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    $\begingroup$ @Freeman This is a good link: adventure.howstuffworks.com/skydiving1.htm $\endgroup$
    – f470071
    Commented Jun 16, 2015 at 11:14
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    $\begingroup$ @FreeMan aircraft have thousands of moving parts working under pressure, force and temperature extremes. If something goes wrong, you will be a statistic. I will be departing before that happens with my no-moving-parts sack of nylon. Also, check your maintenance book and ADs - are you sure it's "perfectly functional"? $\endgroup$
    – paul
    Commented Jun 18, 2015 at 0:17

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