Parachutal stall because of rain shower ..

* Ένα πολύ ενδιαφέρον άρθρο της DHV σχετικά με το πόσο εύκολο είναι
να μπει σε παρασουτάρισμα ένα αλεξίπτωτο ακόμα και μετά από ένα πολύ μικρό ποσοστό βροχής.

Το άρθρο έχει γραφτεί με αφορμή ένα ατύχημα με καινούργιας κατασκευής πτέρυγα 1-2 στην Ελβετία.
Αναλύει στοιχεία τόσο από το συγκεκριμένο συμβάν που κατέληξε σε full stall με επακόλουθο ατύχημα, όσο και από άλλα περιστατικά που έχουν γίνει γνωστά μετά από πτήση μικρής διάρκειας σε συνθήκες πολύ ελαφριάς βροχόπτωσης.
Και αυτό είναι που πρέπει να προσεχθεί αρκετά από όλους μας νομίζω.. 

Διαβάστε το άρθρο στη σελίδα που ακολουθεί..

Parachutal stall accident

 01.08.06
On Sunday 23rd July 06 a serious accident occurred to a Swiss paraglider pilot while flying from the Ebenalp in Switzerland. An experienced pilot was surprised by weather developments and flew through a rain shower. Her paraglider (DHV class 1-2) then entered a parachutal stall, which the pilot was not able to recover from using the standard methods (pulling the A-risers or accelerating with the speed bar). The pilot decided to attempt to land on a steep grassy slope while still in the parachutal stall. Shortly before impact (2m above the ground) the canopy entered a full stall, probably due to brake input. On impact the pilot suffered severe spinal injuries, thankfully with no neurological side effects.

It is known that some canopies have an increased tendency to enter parachutal stalls when wet. It is also known that there are big differences in the reactions of canopies from different manufacturers – some fly quite normally when wet, as has often been reported by cross country pilots caught in rain showers, whereas others report that minimal rain is sufficient to increase the danger of parachutal stalls on their canopies. Last year a school pilot was injured after crash landing in a parachutal stall, after having only flown for a few minutes in very light rain. In the current accident report from Switzerland, again, the rain fall was described as minimal, and the rescue helpers reported the canopy being dry on their arrival at the scene.

Winch tow pilots are particularly sensitised to this problem – a canopy which has become damp merely from lying on wet grass may well demonstrate a higher tendency to enter parachutal stalls.

A pattern indicating which types of canopies are more prone to this problem has not been identified. Occurrences of parachutal stall when wet have been reported throughout all classes. It would appear that older canopies, where the cloth can absorb water more readily may be at higher risk, however, the current accident occurred with a new glider.

It is most important that pilots recognise this potential danger source and act accordingly. Should a pilot fly through rain, the area should be left as quickly as possible, the brakes must only be used sparingly, manoeuvres which cause the canopy to fly with a greater angle-of-attack (e.g. Big ears) should be avoided, and should the conditions safely permit it, the glider should be flown accelerated by using the speed bar.

If a landing while in a parachutal stall is unavoidable, it is most important that the brakes are not used at all, even though this goes against all normal pilot instincts when approaching the ground. When a canopy flies in a parachutal stall, applying a few centimetres of brake may result in the canopy going into an uncontrollable full stall.

Should a parachutal stall occur when flying at sufficient height for a reserve deployment, this should be considered. The advantage here, is that the reserve descent is more stable, and not prone to either stalling or diving as in a parachutal stall descent. The sink velocity of a reserve descent is generally lower than that of a glider in parachutal stall providing the reserve canopy is of the correct size for the pilot. The Swiss pilot reported a sink velocity of -6m/s for her canopy while in parachutal stall.

Karl Slezak

Safety Officer DHV
-------------------------
sourse: DHV
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