Why stay out of the air today?

by Had Robinson
updated December 2, 2021

This essay has cautions about flying in dry areas of the world i.e. the southwest U.S. but other areas not near the ocean coasts can have similar conditions.

A few years ago, I had a discussion with our RGSA Safety Officer, Robin Hastings, on why pilots might want to stay out of the air on a particular day and some things came immediately to mind.  (Be certain to read the Introduction to Weather if you have not already.)

Do we want to get hurt, killed, or wreck our equipment?  It is extremely important that we understand the weather.  The southwest area of the U.S., for example, has some of the most dicey weather in the world because of the dry air and high altitude which can make the thermals very powerful with extreme shear at their edges.  The weather can change so RAPIDLY and/or be completely different just a few hundred feet up or down or a mile or two in one direction or the other.  One minute the air is a pussycat.  Then, in seconds, it can be brutal.  The most important tool is:  STUDY THE WEATHER CAREFULLY WHERE YOU PLAN TO FLY.

Here is a report from an experienced pilot and friend who was flying in Colombia during the 2015 season. She personally discovered why studying the weather can prevent an accident.

Colombia was actually very rowdy this year, with a lot of accidents and one death. I had to throw my reserve the first flight of my first day, heading north towards La Union. I was a couple hundred feet off the ground when I hit the bad air and my wing took two huge collapses on opposite sides and went into a spiral. I threw the reserve and hit the ground 4 seconds later. I had a badly bruised heel and slightly sprained ankle–and I credit my Hanway paragliding boots for saving my bones. My wing was fine and we were able to repack my reserve and I flew the rest of the week, but it wasn't as enjoyable as I had hoped, and the realization of throwing the reserve kind of came in waves afterwards. I have never thrown in 8 years. Everyone said the drought is creating volatile conditions. Water for the city was turned off every day from 2-7pm. There were still lots of low clouds but not a lot of rain in the Roldanillo area. We also got to fly Pietachichu which I thought was beautiful. A fast storm blew in after we landed and two tandem paragliders actually launched into the approaching squall. They really got it handed to them, and right over the buildings–they barely made it with their lives and their passengers. It was unbelievable that they would choose to do that.

Would we be excited in taking the sort of chances these tandem pilots took?  Think of having only one wish: TO GET DOWN OUT OF THE AIR NOW!  But it is not possible.  Would I want to spend the rest of my life like one of these pilots?

Here is an accident report from a regional pilot who pushed the limits, especially the time of day and the season, and experienced serious permanent injuries.  He thought he was paralyzed from the waist down.

Some of you many have noticed that I have been a bit quiet the last few weeks. During the fantastic XC weekend we had in early May, I was in Nevada on a 5 day Volbiv trip. Our intention had been an east west crossing but winds dictated we fly from north to south for a few days and then head north again for the last few days. We were primarily flying the Ruby’s and Diamonds Mountains. The first few days were fickle but fun with some decent XC flight and some adventurous top landing in the big mountains. On the 3rd day the wind switched and we posted up near Eureka and envisioned a 200km flight north. The morning was challenging with 2 guys getting early bomb outs, 2 getting away, 1 (me) scratching and waiting for climb to get up and away. After a bit of scratching I found it was time to land. Below was a sea of waist high sage with a lone green spot as the obvious landing choice. It was turbulent and there was headwind moving toward the landing zone. Somewhere in the 200ft range the wind shifted 180 degrees and to make the grass I would need a low 180 degree turn. Or I could land pretty much any where safely but certainly destroy some if not all of the glider in the sage. So I made the wrong call and went for the tight turn low. On a new wing. And I spun it. I swung through the pendulum of the spin lacking the needed last 10ft of ground clearance. Or, in other words, I was in an accelerated pendulum when I hit the ground butt first. The price was steep. Dislocated left shoulder, 4 broken ribs, fractured sternum, badly bruised ass and tail bone and worst was fractured T8 and burst fractured T9. Upon impact I knew I had broken my back and thought I was paralyzed from the waist down. Fortunately, feeling returned to both legs over the next few hours during the extraction efforts. 6 hours and a helicopter ride later I found myself in SLC at the University of Utah Trauma Center. 12 hours after that I was having spinal surgery. T10-T7 have been fused-8 screws, 2 Pins and 2 rods. A week after the surgery I can walk and generally take care of myself. The pain is still high and movement for more than 20 minutes at a time is exhausting. I’ll be headed home this week sometime. Likely a month of doing not much but sleep and PT. 6 months before a return to a mostly normal life. And a year before I can ski, fly or play sports. Didn’t get bit flying in big air on a gnarly site but landing on flat ground where the hazards were manifestly more psychological than real. Stupid. I'll likely not respond on Group Me for a while as it's a bitch to type or frankly do much right now but hope to see you all in a few weeks for some beers.

The following factors make flying more dicey.  Add them up and it's even more dicey,

  1. Far from the ocean
  2. Relatively high in altitude
  3. Located in the unusually dry Horse Latitudes
  4. Near mountains and deep valleys.
  5. Existence of deep radiation inversions which isolate the air at the ground from the air above.

Briefly, these five factors add up to air that is usually descending (high pressure) which makes for sharp, intense, narrow thermals with rough edges (vertical shear).  Dry air from constant high pressure means few clouds.  Lack of clouds and intense sun makes the thermals very strong during the middle of the day.  Being in the Horse Latitudes ensures that winds are often light and variable and can change direction often.  We can be exposed to different layers of air in the atmosphere as we fly up through it.  That is, the direction, speed, moisture content, and temperature can be all over the place.

The oceans have great thermal mass and air that is next to them tends to be more stable or, at least, predictable, like our southern Pacific coast.  Without careful analysis and help from our local weathermen at the National Weather Service, we can put ourselves in danger quickly.  (I cannot think of any Federal agency other than the military which has saved more lives than the NWS.)

Gust fronts and microbursts

For example, this is what a fully inflated paraglider flying at trim speed looks like after encountering a dry microburst (an intense small scale downdraft) from virga.  It was not a pleasant experience.  It took some serious force to push the glider down like that, overcoming the loading and lift while flying at trim.  Thankfully, the pilot was not cocooned in the glider, there was no cravat, and the glider quickly started flying again.  Furthermore, the glider only contacted the edge of a microburst and did not center it!  Anything else would likely have required a reserve toss over mountainous territory – also a less than good option.  The entire event took less than 3 nerve-wracking seconds.  "[Dry microbursts] frequently develop under benign-appearing showers or virga." - Weather for Aircrews  This was the case here.

paraglider collapse from virga

Salton Sea gust front event Feb. 11, 2012 – Like the southwest and other dry regions, the desert just east of the Sierra Nevada can have sudden weather events that are dangerous to ultralights.  The pilot in the photo below failed to heed clear warnings of a rapidly moving wave of cold air that was moving east across the desert from the Sierra Nevada.  Note the angle of the windsock near the center.  It is sticking straight out, a sign that winds are probably in the high teens.  With help, he was barely able to land without injury or being blown out over water – this time.  Another pilot was, in fact, blown out to sea.  He narrowly escaped drowning and landed on the opposite shore.  Both pilots should have landed immediately but chose not to.  Is it "cool" to risk your life?  Many pilots chose to deliberately play a form of Russian Roulette that day.

When we saw the latter pilot being blown out over the sea we called for search and rescue.  The helicopter and crew attempted a rescue but we had no idea that the pilot had safely landed on the opposite shore, enjoying coffee and food at the home of generous landowner.  It was a huge waste of taxpayer's money.  The helicopter thought ultralight pilots are foolish and careless – often too true.  Irresponsible people like this one make it difficult for the rest of us to obtain access to airports and operating areas.  THESE KINDS OF PILOTS ARE NOT OUR FRIENDS because of the irreparable damage they do.  We are guessing the bill for the Marine helicopter and aircrew was probably $80K.  Suffice it to say, I no longer attend this event because about half of the pilots that attend think responsible operation of an aircraft by a trained pilot is a waste of time.  In other words, they think it is cool to be reckless.

gust front

Per the above incident, I was flying in the mountains to the northwest of the Sea and saw the leading edge of this front sneaking in from miles away (dust kicking up).  The heavy, cold air went along the low areas and then spread out.  The mountains where I was flying blocked the flow and it was probably safe but why take a chance?  I landed ASAP.  But there were many pilots in the air who did not pay any attention to this.  They survived....

dust being kicked up by a gust front

Radiation inversions

Another hazardous condition we pilots face is the formation of inversions at sunset caused by the rapid cooling of the earth through radiation.  This cooling will form a calm, stable dome of cold air next to the ground.  The dome can be but 20' or 30' thick.  Just over the dome, the air can be moving in any direction.

If a pilot launches PPG in seemingly dead air, he may immediately move into air that is moving downwind.  The result is: he falls out of the air.  Hopefully, he has enough altitude to regain trim airspeed – but maybe not.  This happened once to this pilot and a fully inflated glider completely collapsed and everything went into the ground like a sack of rocks.  Thankfully, it was only a few feet but the glider lines went into the paramotor.  A similar situation can happen to a PG pilot when coming in to land, but it is not as serious.  That is, he can be flying into the wind and then enter the dead air of the inversion and the glider may surge forward.  It is all another reason to never do sudden turns within a hundred feet of the ground.

At the "whiching" hour, it is a time when the winds can go any which way.  Extra caution is advised, especially if there is a change of wind direction forecast for that time.  Here is a Radarscope video of a sudden increase of winds just above the surface at the end of the day.  It came out of nowhere.  Thankfully, no one was injured.

Checking the NWS forecasts

Here is a typical analysis of the day's weather from the NWS (this was in the desert) and something that pilots should always check before flying.

The NWS forecast is for some short wave impulses (low pressure waves moving along high in the atmosphere) that are on the tail end of the storm leaving the area.  These impulses cause the air in front of them to go up and cause mixing or gusting (forecast is for the effects to start about 9AM).  Things are calm here both in the valley and at the Dona Ana County Airport but it is because of the inversion which will soon be gone by mid/early morning. Conditions northwest of the Las Cruces Airport and further west of us are different. At 7AM, Deming is already west at 7 mph (not bad).

Things would have been flyable from maybe 7am until 9am but it would rapidly become too strong for all but the best PG pilots (west at 15 was forecast by the GFS model by late morning).  It is the gusting from the short wave impulses and/or lower air masses mixing with the Jet Stream above that should always concern pilots.  It is extremely important that pilots take a look at the hourly weather forecast from the NWS to get an idea of any gusting that might be present or, at least, read the day's forecast discussion.  This is because none of the models are designed to forecast atmospheric turbulence (gusting) that could be dangerous.

So, I am flying at 8:45AM and the gusting forecast was off a bit.  It could be a concern.  For example, I landed late one Saturday and got whacked.  Just as I touched down the winds took off 18+ or so and I got nicely dragged across some of the grass at the operating area.  I knew gusting was forecast for the time I was in the air but it was so nice flying around.  As I went up, wind speed increased and there was turbulence – all signs of something strong coming in.

Getting dragged a bit is one thing (easy, no damage, no harm, etc.) but getting dragged anywhere else?  It could damage equipment and cause injury.  Pilots have been rattled by gusting from the Jet, as well.  It can happen so quickly and is completely without warning.

For example, once I was at the top of Mt. Riley (a high peak in the southwest)  in nice balmy air but I wanted to be sure the Jet wasn't going to do stuff (it often does but I wanted to be sure) so I waited around.  Sure enough, a 35 mph gust came through out of nowhere.  If I had been in the air, probably no problem but what if I was setting up for a landing or had been soaring close to the rocks?  I made the 40 minute hike back down the peak with all of my gear.  Why be careless?  Those pilots who choose to ignore the weather might be lucky but then again....  Today might have been safe for PG for 2 hours or so.  But, to be safe, we should get out of the air an hour before the gusting is forecast.  That leaves a nervous hour to fly.  I did not think it was worth it.  These impulses combined with the Jet can cascade into a dangerous wave of turbulence which is what I think happened when I was at Mt. Riley.  Air and water are subject to the laws of physics and behave in similar ways.  The ocean coasts are subject to sneaker waves.  These are dangerous waves that can be many times higher and stronger than the average wave coming in.  Many have been drowned by these monsters that appear out of nowhere, even on calm sunny days.

The atmosphere can be the same under certain conditions when the effects of extreme winds (the Jet), no inversion to block it, and short wave troughs/impulses which are present and then combine.  Mixing of these effects can cause the dangerous turbulence which can spit a pilot out of the air.

Conclusion:  Get trained by a competent school.  Make sure the air is relatively clean and smooth up to 15,000' MSL or, at least, to the level of a strong inversion before flying in it.  Note: you will not be able to know where an inversion is unless you can read a balloon sounding.  This is why the NWS gusting forecasts are important for ultralight pilots.  Any pilot who has 100's of hours of flight time can tell you a story of how he was just flying along calmly and, suddenly, without warning got whacked badly out of nowhere.  We need to minimize or eliminate these frightening and potentially dangerous events.  That is why we carefully study the weather before flying in it.

Remember that the pilot, alone, is responsible for determining whether it is safe to fly or not.  It is not my job nor the job of the National Weather Service meteorologists.  DO NOT bother them with questions if you have not exercised due diligence in becoming an amateur meteorologist.  Carefully study the material on this website and the Introduction to Weather in the Southwest, in particular.  Fly safely!