Foundations: Sit to Sit Backflip
The four stages of a backflip from head-up, by Axis Flight School...
You end up opening a bit low on the jump… your canopy snivels… your AAD fires your reserve and – BOOM! – there you are under two canopies. What do you do now?!!
In 1995 Performance Designs made a series of test jumps for the PIA technical committee to investigate the characteristics of flying two square parachutes at the same time. The tests expanded on studies carried out by the US Army in 1992 and Scott Miller in 1992/3, by using various combinations of reserve and main (large main/small reserve, large reserve/small main, and small main/small reserve).
Special systems using three or four parachutes were designed, to equip the test jumpers with reliable alternative canopies. The equipment was assembled so the sequence of deployment and cutaway would be as near normal as possible.
The following is a summary of the resulting 1997 Dual Square Report, 1997 and its conclusions (in bold). Full document on the PD website here. Although these tests were done 20 years ago this remains the most comprehensive study on 2 canopies out to date and the conclusions still have validity. But, it should be borne in mind that these studies were not on high performance canopies and did not involve RSLs or MARDs. Such items may change emergency procedures or recommended action. Analyse recommendations alongside your equipment manufacturer's guidelines.
The best way to handle any Dual Square Scenario is to avoid the situation. Use appropriate and available altitude reporting devices to help maintain good altitude awareness. Follow safety regulations on proper opening altitudes. Ensure that AADs are properly maintained and used. Use properly maintained equipment and gear checks.
Some people believe you must choose a reserve smaller than the main. While this is probably a safe thing to do, it is not necessarily required. For example: a PD-143R has shorter lines than a Stiletto-135, this combination flew well in a biplane with the main in front. 7-cell canopies typically have shorter lines than equally sized 9-cells.
Several combinations of canopies were used in test jumps with some greatly mismatched. Canopies with a difference of 100 sq ft. or more could cause results out of the norm. This type of extreme combination is not advisable.
Use great care to choose proper equipment. Choose canopies that are not drastically different in size. A general rule of thumb is to choose a reserve that is similar in size to the main canopy.
In order of probability…
The most likely canopy configuration from a simultaneous or near simultaneous deployment is a biplane, both canopies flying in the same direction with one behind the other. Usually the main is in front and the reserve in the rear. This personal biplane seems to be stable and easy to control. The most commonly preferred method of flying it is to leave the brakes stowed on the rear canopy and fly the front canopy using smooth, gentle toggle input.
With the canopies in a compatible biplane it did not seem necessary/wise to attempt to move the configuration into a side-by-side to cut away the main. In moving one canopy or the other to a side-by-side it always seemed necessary to maintain outside input to one canopy, or the other, or both, to keep them in that configuration. They seemed to always want to return to a biplane.
Cutting away while the canopies are returning to a biplane could be dangerous. In addition, while maneuvering canopies back and forth between side-by-sides and biplanes there were times when the two canopies tried to foul with each other or did in fact foul with each other. It does not make any sense to take a docile, maneuverable, landable biplane configuration and try to change it.
Landing a personal biplane proved to be easy with all canopies – large, small, heavily loaded and lightly loaded. Flaring the front canopy seemed to be the preferred method of landing. However, flaring the front canopy, or both, did not produce a significant effect in the landing. The canopy would pitch in attitude, but it did not plane out or slow in descent rate much if at all. The descent rate on all canopy combinations was very slow, even in full flight. The general propensity to flare high combined with the non-effectiveness of a dual square flare, leads us to believe that not flaring at all is the best way to land.
If a biplane is present and the jumper has directional control, leave the brakes stowed on the rear canopy and fly the biplane using gentle toggle input on the front canopy. Do not flare either canopy for landing, and be prepared to do a PLF.
The next most common configuration is a side-by-side with the main risers behind the reserve risers; both canopies flying side-by-side in the same direction. They are usually touching end cell to end cell, or the end cell of the shorter canopy resting against the outside lines of the taller canopy.
The personal side-by-side was the result of the taller of the two canopies deploying behind the shorter of the two. Whether the taller canopy was the main or reserve, the result was always the same, except for the downplanes that are noted later.
The reference to taller and shorter canopies is to indicate which canopy is longer from the common connecting point on the harness to the topskin of the canopies.
What seems consistent is:-
For the most part side-by-sides seemed to be a configuration that was easy to fly with gentle toggle input from the dominant (usually larger) canopy. It is not recommended to fly this configuration with all four toggles. On one jump, a flare was tried with all four toggles, which immediately turned the two canopies into a nose to nose fighting match – not desirable.
In addition, flaring with the outside toggle of each canopy will turn the dual square into a downplane. This also is not desirable. It must be stressed to only fly the front, or larger/dominant canopy in a dual square scenario. The side-by-side seemed to be more susceptible to instability than the biplane when faced with mismatched sizing and shape. Sometimes with mismatched sizes, the larger canopy wanted to out-fly the smaller canopy. The result would be a twisted-up, partial biplane with the smaller canopy partially in back. The stability of the mismatched combination is marginal in this twisted-up partial biplane, and requires very cautious control input.
Cutting away from a side-by-side that does not want to return to a biplane seems to be a safe action as long as no equipment problems exist, and the canopies are not entangled. It must be noted that RSLs or MARDs were not used in any of these tests. Great caution must be used when cutting away in that scenario due to the varied styles and applications of RSLs.
The jumpers did not feel comfortable landing heavily loaded side-by sides, especially when a highly elliptical canopy was involved. Both the biplane and the side-by-side seemed fairly docile and easy to control – but it is important to avoid complacency. During all of these test jumps the canopies were really put through the works and at times were caused to foul with one another. Strong/erratic control input could cause undesirable results.
If a side-by-side is present and the jumper has directional control, fly the side-by-side using smooth, gentle toggle input of the larger/dominant canopy. Do not flare either canopy for landing, and be prepared to do a PLF. If the canopies do not seem controllable, and they are not entangled with each other, disconnect any RSL, if time/altitude permits, and cut away the main canopy.
A less frequently occurring configuration is a downplane, with both canopies flying away from each other and toward the ground. It always involved line twists due to a tumbling bag on deployment of the main canopy when it was the second canopy deployed. While we did see an occasional flip in a reserve bag, it happened when the deploying lines reached the locking stows. The result in that case would be one, or maybe one half twist, which would untwist as the canopy inflated.
In most cases what started out as a downplane would quickly evolve into a side-by-side with no input from the jumper. In the cases where the downplane did not recover on its own and the jumper did not feel like it was recoverable, there is a question as to whether working the controls of the reserve canopy could have brought the downplane into a side-by-side configuration. This side-by-side would very likely result in a canopy with line twists remaining. This is probably not a configuration that one would want to land, and might still call for a cutaway.
The reason a person is probably in this position is that their AAD fired – so they are already low. There isn't a lot of time to be playing around trying to undo things when that time could be used cutting away and sorting out the best place to land. Being in a dual square situation calls for quick evaluation and quick action. A downplane plummets out of the sky at high speed.
If a downplane is present, disconnect any RSL/MARD, if time /altitude permits, and cutaway the main canopy.
Another fairly common configuration would be a fully inflated canopy (main or reserve) with a trailing pilot chute, bag, and/or trailing uninflated second canopy behind the jumper. If left unattended this scenario would sometimes result in one of the other configurations.
In some cases the jumper found himself under one fully inflated parachute with a partially deployed second parachute trailing behind. It was found to be easy to pull in a trailing pilot chute, or even a pilot chute, bag and lines. Great caution must be used however in doing this. If the canopy should get out into the airstream it could inflate or partially inflate quite rapidly and get out of control. We do not recommend trying to pull in an inflated or partially inflated canopy.
Even a bagged canopy is dangerous to carry around due to the possibility of it getting away from the jumper and inflating. This happened on one jump just as the test jumper was making a turn into final for landing. The result was a late developing personal downplane that caused bodily injury. It might be wise when possible to cut away any canopy that is going to be pulled in and carried to the ground. Trying to pull in a partially deployed parachute can aid in its deployment with undesirable results.
If the main canopy deploys and the reserve is in a stage of deployment it might be best to aid the deployment of the reserve by shaking the risers. Then be prepared to take action on the resulting configuration. If the reserve opens and the main is in a stage of deployment, it might be best to remove the RSL and cut away the main.
We had one simultaneous deployment that resulted in a spinning entanglement of the two canopies. The reserve deployed directly into the deploying main, trapping the main slider which choked off the main canopy's inflation. The test jumper tried pulling risers but, due to the spinning situation, elected not to stay with it past 6 or 7 revolutions and cut away both canopies.
We felt after evaluating the situation that if the jumper had cut away just the main canopy there was a chance it would have cleared. This is however, only speculation.
If a main reserve entanglement should occur, do everything possible to clear the two canopies by pulling on risers and/or toggles. Be cautious about immediately cutting away the main canopy as this may accentuate the problem.
Additional safety devices, such as AADs & RSLs, may cause standard emergency procedures to change. Analyze the release recommendations and be sure they coincide with your equipment manufacturer’s guidelines. Practice these new emergency procedures prior to every jump.
Full report on the PD website here.