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 Заглавие: Падане на тандем в ротор
МнениеПубликувано на: Пет Мар 24, 2023 6:42 pm 

Регистриран на: Пет Мар 05, 2004 4:52 am
Мнения: 2300
Местоположение: Сопот
Име: Николай Йотов
Наскоро в Етиопия имаше интересен тандемен инцидент на едно от най-трудните места за тандеми в света (според Ясен).
Направих му анализ, на английски, за да го разберат нашите местни партньори и посочих различни мерки за повишаване на сигурността:

There was a serious paragliding tandem accident on 12th of March, at about 2 pm, at Haymanot cliff, 5 km south of Aleltu.
After a smooth take off in light easterly winds, the tandem pilot didn’t experience enough lift for ridge soaring and continued down, towards the landing field. After the second terrace, where road to Haymanot monastery starts its steep descend down, the pilot encountered a turbulent zone, which collapsed almost the entire wing, depressurizing it and turning it towards the slope. The pilot pulled the brakes to stop the collapse’s development and tried to steer the wing away from the slope. At this moment, another big asymmetric collapse happened, the wing lost its lift force and both pilot and passenger fall down vertically, slightly backwards and sideways. The fall was on a stony slope covered with 1 meter high bushes.
The pilot’s back protector reduced the impact, but still the pilot got cracked ribs at the central chest part (sing of high energy impact) and bruised/compressed vertebrae at the middle back, probably due to a stone penetrating through the back protector.
The upper part of passenger’s body was protected by the pilot’s body, but still the passenger had a broken hand in 3 places, broken leg and a broken pelvis in 3 places.
After hundreds of successful flights from this place, this particular accident came as a surprise as there were not strong winds and signs of turbulence.
This flying site is one of the most demanding and riskiest places for tandem operations because:
- It’s a cliff take off with multiple cliff terraces, stony slopes and stony fields;
- The area has typical strong easterly winds. Rift Valley narrows between Addis Ababa and Adama, which accelerates the wind flow in the whole region;
- There are strong thermals created from a dry river bed and stony slopes and fields. Warm air is brought along the canyon from far away, feeding powerful thermals;
- The 700 m deep canyon narrows and ends around the takeoff area, which means that its surrounding shores/highlands are close enough to interfere with lift, sink, wind and turbulence.
The most dangerous part is the rotor created by the edge of the cliff with significant wind gradient effect, which challenge take offs and top landings, requiring specific knowledge, skills, focus and performance how to avoid them, but also to use them.
Another serious concern is the powerful thermals with their associated turbulence which can hit anytime, anywhere. There were small dust devils observed at flatlands behind (west) of take off.
Still, the plenty of lifting air, road access and stunning view make the place good for tandem flights, helping passengers cure their fear of height, enjoy flight and appreciate the beautiful Ethiopian landscape.
Unfortunately, paragliding accidents happen, as in any new and dynamic activity like car driving, airplane flying, horse riding, skiing, etc.
Fortunately, paragliding accidents can be successfully analyzed and used for increasing flying safety. They require an honest and truth-seeking approach, avoiding blame-games and shaming pilots, equipment, organizers, etc. It’s a year’s long lasting learning process.
The analysis of this particular accident reveals the following things:
A light wind or no wind at takeoff can be a misleading sign for good take off conditions. There were no nearby signs suggesting strong wind at lower altitude, which to create a turbulent zone here or there. The reason for this low-level strong south wind was probably a cumulo-nimbus (Cb) cloud development southwest from takeoff. 5 minutes after the accident there were 2-3 thunders, which usually happen either when the cloud grows rapidly, either when its heavy rain falls, working as a conductor between the differently charged cloud and earth.

It is not uncommon, pilots to fly with Cb clouds around and this depends on local terrains and conditions. For example, big sharp mountains like in Alps make Cb clouds grow big and fast, creating powerful gust fronts channeled and further accelerated by deep, steep and narrow valleys. From the other side, rounded forested mountains surround by vast flatlands, like those in central Bulgaria, make Cb clouds grow slow, their development, movement and gust front spread along mountain ranges and river basins, which allow for relatively safe flying, when there are thunders and lightening 10 km away.

In this particular day, conditions started with a cloudy sky, which at noon grow to isolated cumulus congestus clouds. Later, some unite into bigger cloud masses, others dissolved. During take off, there was an isolated small shower 10 km upwind, east, from takeoff, which would create a weak gust front from east. About 20 km South and South west from takeoff there is a big blurred cloudy mass, which is the possible source of the strong southerly wind below take off. In this situation it is difficult to predict which will prevail, where would wind come from? Additional problem is to predict how wind is modeled in this rugged terrain. A deep canyon may work as a barrier for some winds and as a conductor and amplifier for others.
As learning all local features and weather effects takes years and hundreds of flights, a safe approach would be DON’T FLY WHEN THERE IS OVERDEVELOPMENT AND RAIN WITHIN 50 KM. The bigger the overdevelopment, the bigger is this distance. Ethiopian 2400 m amsl highlands make cloud develop much faster than other places. The rain is not the only reason for gust fronts and surprising winds. Powerful lift, with or without clouds, creates a compensating powerful sink, which may have similar effect like gust front from rain.
On approach to the edge of the second terrace, the paraglider experienced some turbulence, which should be a warning sign of possible bigger turbulence ahead. This, plus the southerly wind indicated by the vegetation and paraglider’s drift seen by its ground speed, should hint the pilot about a possible bigger turbulence ahead caused by the ridge to the right. Therefore, EXPECT ANY TURBULENCE AS A SIGN OF BIGGER TURBULENCE AHEAD AND TURN SLIGHTLY DOWNWIND IMMEDIATELY!
4 seconds after the first turbulence warning comes the first collapse. There is not much do be done afterwards. The first collapse turns the paraglider towards the slope, which is typical for rotors to suck-in wings inside the vortex. Brakes are not efficient to control direction. Airspeed is low and easily lost. A collapse (caused by low angle of attack) can easily transform into stall (usually caused by high angle of attack). The turbulent, “dead” air makes collapse and stall recoveries long. The pilot tries to control and recover the wing (the spin?), but perhaps, a full release of brakes would give some chance for a miraculous last moment recovery.
Pilot’s harness back protector made of foam really helps for such vertical/backward falls. Passenger’s harness airbag didn’t protect much, probably because it met first 1 m high bushes and then the hard stony surface. The fall is also sideways, while an airbag protects only from underneath.

Depending on its body weight the passenger is being attached to a higher or lower attachment point as spread bars connecting pilot, passenger and wing work like scales. If pilot is heavy and passenger is light, then passenger will be lifted high, obscuring pilot’s forward vision. If passenger is too low then it will leave ground last at take off and meet it first at landing. It is recommended always to ATTACH PASSENGERS AT HIGHEST POSITION because the pilot is more experienced in running; he should leave ground last at take off and meet it first at landing. This means that the pilot should adapt for the restricted forward vision and will suffer more injuries in case of vertical/backward fall. When having passenger at highest attachment position, make sure that pilot’s legs and harness are not deforming or compromising passenger’s airbag, especially when using soft spreaders with shorter distance between pilot and passenger.

Additional factors for the accident are connected with the organization of tandem flights. In this particular accident, the tandem operator used a new driver who then refused to drive down on the dirt road to the bottom landing field. This slowed down the whole process delaying flights with 1h 30 min. This was the second flight of the day out of 6 planned and it happened quite late – at 2 pm, when is usually the peak of Sun’s heating and cloud development. IN MORE DIFFICULT CONDITIONS, PILOTS SHOULD BE GIVEN LESS FLIGHTS AND ORGANIZATION SHOULD BE EARLY AND PROMPT.
THE PILOT CAN CANCEL FLYING AT ANY MOMENT AND ORGANIZERS AND CLIENTS SHOULD KNOW AND ACCEPT THIS. THERE SHOULDN’T BE ANY PRESSURE ON PILOT AFFECTING DECISION MAKING AND SAFETY. Paragliding in Ethiopia is more demanding and risky than elsewhere. It needs very experienced pilots, who are difficult to motivate to come for little money. Pilots are expensive, equipment is expensive, transport is expensive, clients pay little and all this compromises safety.
IT IS SAFER WHEN PARAGLIDING OPERATIONS HAVE OPTIONS AND FLEXIBILITY. ANOTHER PLACE, ANOTHER DAY, GOOD VEHICLE. The idea of having 2 take offs in Sendafa and Haymanot is not only to reduce financial pressure from land owners, but also to give the pilot a choice which place to use according to the conditions. Last year we had 2 flying sites. This year we stopped negotiations and lost Sendafa. Then we lost the original starting place above Haymanot and had to move to another one along the cliff. Tandem organizers also started to avoid Sendafa, which allows for much safer flights, because its road is tougher than Haymanot. Perhaps the price of such an accident is higher than the extra transport costs.

Again, no blame to anyone. It’s a learning process for all, for bringing a new service to Ethiopia adding high value to tourism, sport and recreation.
PASSENGERS SHOULD BE WELL INFORMED ABOUT THE RISKS IN PARAGLIDING AND AGREE TO PARTICIPATE IN WRITTEN LEGAL-PROVE FORM (indemnity form of informed consent). Pilots and organizers cannot bear the whole responsibility of such weather dependent activity like paragliding.
Don’t forget the additional risks accompanying paragliding, like transport to/from flying sites, take offs, landings. Non flying passengers and bystanders often stay in a wrong position during a take off and landing and there is a real risk for accidents with non-flyers, especially at cliff take off. Paragliding organizers should assist pilot’s with their take offs and top landings (helping with the wing), but should also manage clients, kids, farmers, livestock, etc.
It is very important to have good relations with the whole local community, not only with the farmers which land is used for take offs and landings. For example, safe tandem paragliding requires wind sock indicators placed at several places, at least at take off and landing, and these are often stolen or sabotaged by locals.
Paragliding is still new for Ethiopia but paragliding operators should engage insurance companies for providing ADEQUATE INSURANCE COVER of medical transportation and treatment costs in case of such accidents.

п.с. днес имах 3 полета от същото място. На последния бях изненадан от условия, подобни на тези от инцидента, но тъй като вече го бях анализирал, аз бях подготвен и отдалече заобиколих турбулентната зона.
Явно в определени условия каньоните правят шашави ветрове.
Излитам с поривист умерено силен И вятър и 100 метра под старта навлизам в усилващ се ЮЗ вятър, даже падащ за И склон от който летим. Веднага щом го усетих избягах наляво, на СИ. В средата на цепката, далече от терена и турбуленции завих срещу вятъра, избрах друга кацалка и така до земята летях в ЮЗ вятър. По прогноза бе ЮИ, на старта бе И. Имаше разни конгестуси, но без дъжд. Пред старта минаваше дълга облачна конвергентна линия, която тръгваше някъде от юг, а над каньона ставаше рехава. На качване горе след втория полет забелязах необичаен Ю вятър на излизане в платото.
Явно зоната на старта прави лъжлив И вятър в тези условия. В основния зимен сезон нямаше и помен от ЮЗ вятър. И горе и долу си духаше стандартния И. Сега времето се дестабилизира, валежи, цебета. Явно е някакъв местен ефект, който може да изненада всеки пилот.
Подозирам, че този вятър е свързан с една по-голяма около 500 км дълга конвергентна линия, която сега е в източната част, в началото на етиопските планини. В Адис и Сендафа днес и по порогноза и в реалност имаше ЮЗ ветрове, които после завъртяха на Ю.


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