Statement regarding spiral dives with the Mistral 6

23 July 2012

Swing wishes to make a statement regarding spiral dives following the fatal accident at the Kandel, Germany. Any accident is of great concern to us and we would like to express our sincere condolences to the family of the pilot involved.

Swing has always placed great importance on safety. This matter is of particular concern to us and we are in the process of analysing what occurred and what contribution we as manufacturer can make to prevent such accidents from happening in the future.

The Mistral 6 was developed under the premise of "performance and handling". Our research and customer surveys indicated that what the market was looking for at that time was greater performance and more agile handling in all classes. This was possible in terms of design because changes were then being made to the certification requirements (LTF -> EN) as well.

Gliders were developed which demonstrated these features but which, on the other hand, in some areas at least, demand greater pilot skill. We were very proactive in dealing with this fact, addressing it both in the instruction manual and advertising and also in our advisory talks.

A high-end EN B glider is not a DHV 1/2 glider and nor is an EN C glider a DHV 2 glider. This means that the Mistral 6 is more demanding than a Mistral 5.

When an incident occurs, there is a tendency to say that the glider was the sole cause, whereas it is in fact the only constant factor in the interplay between glider, pilot and harness. The glider always remains the same, but every harness, pilot and pilot position in the harness creates new combinations, which as a rule were not tested in exactly that combination.

For a pilot's own safety, s/he should carefully examine the particular combination and situation and study the relevant manuals from the glider and harness manufacturers. In addition, when purchasing a glider, the pilot must without exception be briefed by a flying school about the new paraglider and its special features, as is usual in other branches of aviation.

After the accident at the Kandel, we immediately conducted test flights once again using a range of parameters (harness types/adjustments/pilot positions). These confirmed the previous findings and we have reached the following conclusion:

 

  1. the Mistral 6’s behaviour in a spiral dive is as described in the instruction manual (LINK)

  1. the harness geometry (e.g. carabiner-seat distance / width of chest strap) has a significant impact on behaviour in a spiral e.g. very closely positioned chest straps favour a stable spiral dive

  1. generally, before a stable spiral occurs, there is a large collapse or an error in beginning the manoeuvre

  1. it is possible to control a stable spiral and recover from it even at sink rates of > 20 m/s

  1. with the other manoeuvres, the Mistral 6 shows very straightforward behaviour for a high-end EN B glider, see also DHV (see test flight reports)

  1. the Mistral 6 can be flown safely if the information in the Instruction Manual is followed and spirals are also possible and safe with the appropriate training

To avoid further incidents with spiral dives, we would once again request that all pilots familiarise themselves with careful and active entry/recovery from the spiral dive. We advise all pilots to get the feel for this manoeuvre slowly, ideally under professional instruction over water.

 

Spiral dive technique

The spiral dive is the most effective method for making a rapid descent, but it is also the most demanding method. Sink rate is between 8 and 12m/s and even higher in an extreme case. Thorough training is necessary because of the complex technique and the high level of physical strain.

Carrying out the manoeuvre

- Starting from the basic position, the glider is put into a steep turn by the use of weight-shifting and by quickly releasing the outer brake and applying the inside brake in a measured but consistent manner. There is a rapid increase in centrifugal force and sink rate.

- The transition from the initial phase into spiral flight then follows after 1-2 revolutions, with even more marked acceleration by the glider. The pilot keeps the paraglider in a controlled sink rate range by ceasing to weight-shift and by using the outer brake. During the manoeuvre, the pilot should look towards the inside of the turn, not at the glider or at the centre of the turn - this could cause feelings of dizziness.

- To recover from the spiral dive, the sink rate is reduced over at least one revolution by braking more on the outside and gradually releasing the inside brake. If the glider then shows a tendency to straighten, the inside brake is applied gently once more and the remaining energy is spent in a final circle.

- The spiral dive must be completed with at least 200m height above ground remaining. The recovery stage must therefore begin at an even higher altitude.

Pilot error and risks

- A stable spiral dive can be caused if there is too much acceleration after beginning the manoeuvre, and the pilot does not reduce this by the use of weight-shifting and applying the outer brake. Sink rate in the spiral dive should not exceed 10-12 m/s.

- Spiral dives with high sink rates can lead to feelings of dizziness, black-outs or loss of consciousness. The pilot must immediately exit from the spiral dive at the first sign of any physical impairment.

Risk of stable spiral dives

There is generally no problem in recovering from a moderate spiral dive with a sink rate of 8-12 m/s. With a higher sink rate, the pilot must be prepared for the glider to carry on turning over several revolutions, or even for a stable spiral in an extreme case.

Correcting the manoeuvre

- To actively recover from this flight position, the paraglider must be given clear pilot input to fly normally. This is done by weight-shifting against the turn direction and strong symmetrical braking. If this slows the spiral flight the glider will recover normally.

  • Deploy the reserve immediately if attempts to correct the manoeuvre fail or if you lose control of the glider.
  • A sink rate of 10-12 m/s should not be exceeded during training or in an actual case.

There are also a number of specialist articles (in German) on this topic on the DHV website at www.dhv.de.

Conclusion:

To date, there has been nothing unusual at all with the Mistral 6, apart from the behaviour in spiral dives (outside the limits tested by the DHV > 14m/s). There are high G-forces in a spiral dive which can quickly lead to a black-out for those who do not have training. We advise all Mistral 6 pilots to familiarise themselves thoroughly once again with how to begin and exit from the spiral dive and to practise this ideally during performance training over water or, if a pilot has any doubts at all, to refrain from using this manoeuvre. Our general advice is to begin a spiral dive only with sufficient altitude and with additional safety reserves and to recover from the manoeuvre with a minimum of 250m ground clearance.

Unfortunately hindsight has shown that at least some pilots in the target group were not able to manage the Mistral 6’s behaviour in a spiral dive. We would like to apologise for this. We sincerely regret what has happened.

As for the prototypes which are currently being developed for the future EN B generation of gliders, we will be even more critical when testing safety-relevant manoeuvres, going even further than the prescribed operating and certification limits in the EN standard.

Günther Wörl

Geschäftsführer

SWING Flugsportgeräte GmbH