Mard (skyhook) reserve opening issue

[Youradhere 0]

I heard about an interesting scenario and I want to know how common it is. 

I read this in an article on uspa.org

Quote..

"If you are below 1,000 feet, you should still go straight to your reserve and get more nylon over your head. However, you should be aware that there have been cases in which a MARD hindered reserve deployment when the jumper pulled the reserve ripcord while still attached to the main parachute. In these cases, the reserve pilot chute launched but did not have enough drag to disconnect the MARD and pull the reserve from the container"

 

It says "there have been cases"... does that mean this is rare but possible?

is it particular to a certain brand of mard? Do some do it more than others?

 

here is a link to the full article 

https://uspa.org/Information/News/mardshow-they-work-and-what-to-expect

 

[skytribe 16]

In simple terms the MARD has to work in two ways - to be connected using the departing main as a sort of reserve pilot chute equivalent in the event of a cutaway instead of the reserve pilot chute in order to extract the freebag/reserve canopy.   OR disconnect the MARD in the event of a total malfunction when the reserve pilot chute is being used to deploy the freebag/reserve.    

If you have a slow speed malfunction and chose to deploy the reserve without cutting away the main then your are depending upon the reserve pilot chute to create enough drag in order to extract the freebag/reserve.    There is a great difference in the amount of drag that can be created by a pilot chute at 120 mph and at 15 mph.    At 15mph the pilot chute may simply not be generating enough drag to do the job and may simply trail behind you and not have enough force to extract the freebag/reserve.

If you would have cut away at a correct higher altitude then your main would be acting as the big high drag pilot chute equivalent.  This creates a whole lot more drag than a reserve pilot chute even at slow speed.    Even without a MARD and just an RSL cutting away would result in you accelerating to a higher airspeed which would result in more drag on the pilot chute and a successful deployment - albiet with a loss of a lot more altitude.

So yes there are scenarios when not cutting away and pulling the reserve may not result in a reserve being extracted from the freebag and inflating.    The best action is to avoid this scenario in the first place.    Pull at the correct altitudes, know your emergency procedures and be confident in execution at appropriate decision altitudes.       Not cutting away and pulling reserve under 1000ft is probably the culmination of a number of bad decisions.

 

[pchapman 261]

Someone else may have a better take, but I'll take a stab at the issue, although I don't personally know of any cases:

Some MARDs disconnect from the pilot chute with almost zero force, and some companies think that is a positive feature. In contrast, the UPT Skyhook MARD is tacked in place, so it takes some pounds to disconnect. That can also be seen as a positive, by preventing unwanted disconnections when the reserve bridle is whipping around in the burble as it starts to pay out. That makes the MARD feature more reliable. I'll now leave that argument aside, whether a MARD should best disconnect at say 0 lbs, 1/10 lbs, 5 lbs, or something else.

It may also help in cases of an accidental reserve opening after a main opening -- The Vector pilot chute might not disconnect from the MARD RSL, which in turn is solidly velcroed to the harness, keeping the pilot chute from dragging out the freebag. 

That's good if you don't want a two out. But in case of a slow speed mal at very low altitude where you did want more nylon out, would that connection hinder reserve deployment? I would expect it to only be an issue in certain rare situations, where the airspeed isn't too much.

The Vector PC, while it has worked just fine in huge numbers of uses in some of the world's most popular rigs, is also one that has particularly low drag, so when on a shortened bridle (just to the Skyhook) in the burble of a jumper, it might have a slightly harder time popping the Skyhook seal thread and then extracting the reserve bag from the container and reserve from the bag.

How much force it actually takes to disconnect, and what happens in practice under slow speed flight under a main, I'm not sure. (Force to break the seal thread on the Skyhook will depend on actual geometry and knot strength reduction factor, and isn't simply a matter of taking the tensile strength of the thread alone.)

 

 

 

 

 

[sundevil777 93]

Therefore, when in the low basement and wanting the reserve out, throw out the main pc and cutaway in one smooth motion...problem solved

Edited March 18, 2019 by sundevil777