Iguala is a desert thermal site with mountain ridges pushing up two to three thousand feet about the valley floor. I didn't know of any specific thermal convergence zones or shear situations. Some background about another variable here, me the pilot: I have a fresh new Advanced rating (para-IV), 325 flights, 165 hours of airtime, and a few hundred XC miles in alpine and desert thermal conditions. I've been flying for almost 5 years, and I've been through one complete advanced maneuvers clinic, though not with the performance-rated wing I currently fly, on which I've got about 65 hours. My nickname is "Medium Dog" -- not a Big Dog, not a pup. This all makes me quite prone to intermediate-syndrome and a false sense of security. I was aware of this, but too often my lust for big flights gets the better of me.

My cross-country flight was off to a good start, about 13 miles from launch. I had flown along this ridge without incident earlier in the week, but I was a little tense. Launch was too far away for any of the advice I'd received there to apply to this ridge. I was psyched about trying again make it all the way to Lake Tequesquitengo, another 10 miles or so north. I knew I had to cross this ridge but I didn't know how or where, just that I should be higher first, and that I couldn't run to the end of it. I'd been rotored down there, at Cerro El Jumilar, a few days before. This time the prevailing and valley winds were moderate, the lift was mostly thermic. As I ran along perhaps 600 or 700 feet above the ridge, I got out my camera and shot a photo of the mountaintop. 30 seconds later, I hunted for lift over the green spur in the upper left of the photo. Finding little, I ran around the near rim of the bowl just visible in the top of the photo. I was conciously thinking about rotor and mechanical turbulence, but the winds were moderate, and I was at least 500 feet above the terrain, probably more. Nevertheless, that's when I found it, or it found me. I've since learned the saying "If you could see the air, you wouldn't want to fly there." I was about to meet some Ugly Air, and it didn't make a good first impression.

My wing surged a bit. No big deal, this is what active piloting is about. Ten seconds later, still running with little or no brakes on as usual, I took an extremely large asynmmetric collapse. Small ones of less than 50% are familiar and no big deal. I've been told I can reduce these by flying with more brakes, but I often like more speed. This is probably bad piloting, more on this later. Anyhow, this collapse was a big one, 75% or so. A tiny triangle of wingtip remained inflated, surging extremely hard and fast, sucking the deflated mass into its taut lines. I've handled this big a collapse only a few times, but recently and successfully. The stall speed goes up with less wing flying, so I countered gently, expecting that it might go negative. Still out in front of me and wanting to deep spiral, the wing obliged me and went negative. I instantly threw both hands up. Though still not flying, the wing mostly reinflated for the briefest instant before taking a full frontal collapse and horse-shoeing. How can a full frontal happen when you have no airspeed? This didn't make sense to me, and it was getting pretty violent.

Unbeknownst to me, instructor Dixon White had almost caught up with me. I heard him say "Ooh, ride 'em cowboy!" over the radio. Seems someone always says something like that while a pilot has his/her hands full of something like this. When I checked my vario (long after the flight ended), it read a max down of 2,040 fpm, or about 23 mph. That's down. As I continued to lose altitude and fight my wing, Dixon's voice returned with critical constructive advice at this point, saying "Um, you should think about throwing your reserve." I checked the horizon a couple times but my attention was still too tightly focused on the chaotic acre of fabric more or less above me.

I've been through a couple of reserve clinics, and am able to throw my reserve in under 3 seconds. I routinely grab my reserve handle twice before each flight, for practice and to train my "muscle memory". I've listened to every story I come across, about people who've thrown their reserves. When possible I've asked those pilots questions about their experiences. I always thought I'd just recognize when the time came to "throw my laundry."

As it turned out, the weakest link in my reserve system was still me, the pilot. I never even made a conscious decision whether or not to throw it. I rode my problem all the way to the ground. My corrective piloting skills had never let me down before, said as though the air doesn't play a deciding role too. That's ego alright, intermediate syndrome. I knew no limits. I had faith that it would just clean itself up. It's hard to admit to myself and to my loved ones that I should be dead from that mistake. If you allow five or ten seconds for correction attempts, I had at least a five-second window in which to make the decision, not a lot but enough. In the last several seconds, as my still-not-flying wing turned and I pendulumed beneath it, I realized the time to throw my reserve had come and gone. At least my body assumed the PLF posture automatically.

The critical instant came and went. It was quiet and I didn't hurt. I opened my eyes to find myself dangling from a tree growing at a 45-degree angle out of a cliff. I'd been caught like a baseball in a catcher's mitt. I was intact, and so was my wing. Who could avoid pondering divine intervention in such a circumstance? Little did I know, the adventure was far from over.

After radioing to my amigos that I was OK, I swung back and forth to get my feet onto a narrow dusty ledge and unclip. I looked up through the branches to see my wing. (SLIDES 2,3,4) The nearest "branches" proved to be roots; the whole cliff face was eroding dusty dirt. The tree was thin, dying, dry and brittle. Gee, great. As I started cautiously out on the trunk, I listened for cracking. I went as far as I dared and freed much of the wing, before hearing a sound like rain. I looked to see dirt trickling from the tree's roots. I hurried back, and used a branch to free the rest of the wing. I stuffed my wing into a sack and had to carry it, too big for my backpack and no room to fold it.

I was only 50 feet or so from the top of the cliff, but it was sheer vertical rock. I wished I'd tried rock-climbing but because I hadn't, I had to head down into nasty rough stuff. Some pilots ride in 4x4 vehicles all the time, not me. I hike up to launches most chances I get. The hike down would be "bush-wacking" without a blazed trail. I scrambled from ledge to ledge down the cliff, into a ravine full of downed trees and dense vegetation (PHOTO). I'd never before seen real vines like the kind Tarzan uses for his commute. Huge boulders formed a dry creekbed down the center of the ravine, complete with dried-up waterfalls. I think this was a worst-case scenario, and made for slow going. Ok, a swamp would have been worse maybe. I dropped my wing down in front of me, and slid down the boulders, some the size of a house. Between the rocks and the vegetation, I got pretty scraped up. I fly with enough water for a typical flight and short hitch-hike. This is not enough for the kind of contingency in which I found myself. I was out of water within an hour.

The ravine ended abruptly, emptying 300 feet straight down into a basin. Now what? At least I had a beautiful sunset to take in. I spoke with my friends on the radio. They were enjoying cervezas at a restaurant near town, 1,800 feet down and a couple miles distant. They encouraged me to bivouac. The week before, the story had gone out about a hometown flying instructor who'd flown the area recently. He ended up landing far from a road and spending the night. This did not sound inviting to me. I was thirsty. My friends wanted to go back to their hotel in Taxco, and I wanted to go with them. The story about the guy who spent the night had at least inspired me to pack a small flashlight and a headband. This proved very useful. I pressed on in the twilight, lowering myself hand-over-hand between saplings and exposed tree roots down the cliff.

One of my friends, Dave Norris, took the initiative to do something to help me. I had bought a GPS unit the week before my trip, and so was able to get a fix and read to him my coordinates. He found my position on a good topographical map, and drove into town to find a local who knew the area. He found just the guy. Upon showing him the map, the local directed Dave to the nearest point of civilization along my ravine: a ranch, that his cousin happened to own. Dave drove out there. The road was Truly Nasty, in fact it broke the chassis of the VW bus Dave was riding in.

By now it was well after dark. My only comfort was the voice of my friends on the radio. Though sometimes the news was decidely uncomforting: I asked about plants or animals to watch out for, and was told that the area was home to rattlesnakes who like to slither out onto the sun-warmed rocks after dark. What do you do upon learning this? You don't want to press on, yet you don't want stay there either. After 5 hours coming down more than 2,000 feet, I was fatigued and somewhat dehydrated. Dave was within shouting distance now, but he didn't have a flashlight. Somehow he scrounged up a blinking-red bicycle tail-light, 3 red LED's. He actually used this for a light and hiked 200 yards and down a steep face into the ravine. He brought 2 liters of water with him. Dave is a great friend for doing that. At 11:30pm, five and a half hours after starting 2,100 feet down the mountain, I emerged from the ravine.

CONCLUSIONS

1. The Buddy System: whenever possible, fly with others.

2. More Brakes. The sky-gods all talk about letting out their trimmers and running fast to the next thermal, but it can be dangerous to over-generalize about the merit of this. Rough conditions like strong thermals call for the significant added security afforded by flying with some braking.

3. Ugly Air is out there. After much discussion with mentors and others I've added two new words to my vocabulary: thermic convergence. The more you know about forms of turbulence, the better prepared you are for avoiding or handling problems caused by flying into them. (See the sidebar on Ugly Air.) It's a good idea to talk with instructors and other pilots to learn about the air. Hang glider and sailplane pilots have often been flying a lot longer than paraglider pilots, and seem to be a good source of insight about the air.

4. Throw your reserve. If your wing doesn't clean up quickly, err on the side of throwing it. Nothing feels worse than realizing it's too late and you're going to crash. I don't know how anyone could prepare me to know when to throw it, maybe I just had to live through this to learn. This deficiency in my judgement and piloting skills is the hardest and most humbling reality for me to face. Hopefully you would have thrown your reserve in the same circumstances.

5. Carry gear for contingencies. Your needs are greater when things go wrong, so don't pack for the successful case only. Extra water, a tiny flashlight, GPS, a small first aid kit and some energy food are very useful. While this is true for XC flights over remote terrain, it's sometimes also true for non-XC flights. It's pretty easy at many sites to go down a couple hours hike from safety, especially if significant vertical terrain is involved.

Most intermediate or advance pilots seem to have at least passing knowledge about mechanical turbulence, rotor, shear layers, the sink around thermals, and turbulence near an inversion boundary. But I've met very few who claim any knowledge of thermic convergence. Here's what I've been able to piece together about this.

Thermic convergence occurs where two or more distinct thermals are drawn together and merge (converge) into one larger thermal, or where one thermal is meeting some other non-thermal kind of airmass. The interface where this occurs can be smooth, but more often it's turbulent, sometimes even violent. The convergence may be caused by terrain or weather, and may occur high above the terrain or low near it. For instance a likely place might be the top of a mountain that has several thermal sources below it. The thermals will sometimes run up the mountainsides and all converge at or above the top of the mountain. Chelan Butte is sometimes home to this phenomenon.

Thermic convergence may also occur high above any terrain. Just because you're high enough to be free of mechanical turbulence does not mean you should relax. You can't usually see thermal convergence, but it sometimes pays to look anyway: Dixon White recommends keeping your eyes peeled for airborne debris riding in thermals, sometimes quite high even, allowing you some limited visual evidence of what's going in the air around you.

Another potential high-altitude turbulence phenomenon is suggested by Joe Gluzinski. He believes that a strong thermal can behave like solid object and cause mechanical turbulence or lateral rotor downwind of it as a prevailing wind blows around it. This might warrant extra caution on the downwind side of your thermalling turns.

Clearly there is more to be known about this than I currently know or have covered here. If you're going to fly in strong thermal conditions, it pays to seek as much knowledge of this as possible. Instructors are usually knowledgeable about this. Hang glider pilots often fly some of the same sites as paragliders, and often have been flying a lot longer. It's good to talk with them about it.