Microbursts & Gliding
It’s been a few weeks since our friend Shmulik Dimentstein died in a tragic crash of his HpH Shark just as he was about to land at his home airport Rifle in Garfield County, Colorado.
As I’ve written before, soaring is objectively dangerous. Per activity hour, the risk of dying is about 40x greater than when driving a car.
However, we also know that it does not have to be so dangerous. About 90% of accidents could have been prevented by the pilot. Most can be avoided by diligent pre-flight preparations; paying attention to what’s happening around us; staying disciplined and flying within one’s margins, and avoiding basic piloting mistakes through regular practice. The 10% of unavoidable accidents tend to be the result of particular mid-air collisions, medical problems, or – very rarely – equipment failure.
So when a pilot you personally knew to be all of these things – experienced, disciplined, diligent, observant, careful, as well as current – becomes the victim of a fatal crash while landing at their home airfield after a successful flight in typical summer soaring conditions, it gets your attention.
And when all signs point to a “stall and spin” during the final turn to land it really makes you wonder what happened. “Stall and spin” accidents in the pattern, although quite common and often deadly, are usually easy to avoid. Pilots just have to enter the pattern at a safe altitude and fly at a safe speed. We all know about the yellow triangle and adding an extra margin for wind and gusts. Could Shmulik have made such a basic mistake? Having flown with Shmulik myself, I immediately found that implausible.
It turns out my instinct was right. This accident was not the consequence of a simple mistake. If you or I would have been in Shmulik’s position, I doubt we would have done anything differently. If you find that disturbing you’re not alone.
As you will see, Shmulik was supremely unlucky. He literally flew – or fell – into a microburst, an invisible, deadly, trap. Which made me wonder: must we simply rely on luck to avoid the same outcome?
Well, after giving this a lot of thought, I don’t think so. Nor should we. There are things we can and should do differently if we face similar conditions in the future. As we probably will.
I will present them after a detailed analysis of what I believe happened to Shmulik.
A First-Hand Account by Rick Roelke
I’d like to start by re-printing a very insightful write-up of the accident by Rick Roelke who was one of four glider pilots flying that day from Rifle. John Good published Rick’s report on RAS. I will come back to Rick’s account throughout my analysis as it is essential to understanding what happened.
“Four gliders flew out of Rifle on June 9th, 2022. We all launched around 11:00 and moved to the north side of the valley. It was tough to find that first good climb, but Shmulik found one, leaving the rest of us floundering low. Eventually, we did get away. Long story short we all ended up going in different directions, all having great flights. They were not without challenges but nothing spooky, just enough work to be rewarding. In a flight of about 600 km, Shmulik made his goal of Duchesne UT and was happy about that. We made plans to be on the ground at 6:00 and all converged on the Rifle area in time for that.
There was virga in the area, and it got my attention as Shmulik had warned me on a previous trip to be careful with local virga. I was listening intently to the ASOS for wind or gusts, letting it repeat 5 or 6 times with the exact same report: 9 kts straight down the runway; no gusts. Later, as we got ready to land, the same benign report. OK, I thought – the virga is clearly a non-issue. As we will learn, it was the whole issue.
There was virga over the airport (elevation 5537 ft) and to the north of the valley, and northeast as well. None of the wisps extended below 11,000 ft (cloud base was approximately 19,000). Cloud cover was scattered. The clouds producing virga were not towering – they were perhaps a bit bigger than non-producing clouds, but not much. It was a point of interest to me as we don’t see a lot of it in the eastern US – I was wondering what drove the difference.
Shmulik and I discussed the landing order: as he was a bit lower we agreed he would go first. After we decided this, we heard a Challenger jet announce “Taxiing to 26 for takeoff”. That was the runway we would use to land.
Rifle has a moderate amount of bizjet traffic; not constant but present. We always try to accommodate and be polite citizens. Shmulik called the Challenger and offered to delay but got no reply. I was still high so it was no problem for me. He tried again, with no reply. It’s worth noting that Shmulik had a close call in the past: a jet pulled onto the runway in front of him with no radio call. This near miss was avoided only by the jet taking off immediately in front of him. I am sure he did not want to repeat that. I speculate that the Challenger was on a different frequency temporarily, perhaps the ASOS.
As he descended, he called that he was in heavy sink and was going to make left traffic for Runway 26 (for which the normal traffic pattern is right). Shortly after this, a call came from the Challenger that there was a glider crash.
I was not sure I’d heard it correctly so I asked for clarification. “There has been a glider crash and we see no movement.” They truly had a front-row seat, as moments before they were hit by a gust so strong that they had rotated their jet to avoid a compressor stall.
I then asked if the runway was clear, was told yes, then landed uneventfully into the 9 mph headwinds. I am not sure of the time between our landings – I would guess it was 5 min. The other glider pilots landed without problems, though all could see the wreckage of our friend’s aircraft which left no doubt as to the outcome.
The last moments of the crash were recorded by an airport security camera. We were allowed to view the footage (but not record it). It showed Shmulik in a moderately steep turn, apparently carrying a lot of speed. In the background, you can see dust and gravel being blown by the gust. Then at 90 deg to the runway and 150 to 200 ft you can see the inside wing start to drop and the nose go down. There was no opportunity to recover and it hit the ground hard, thankfully just out of camera view.
The Rifle ASOS recorded a gust of 43 mph from the south: a 100-degree shift in direction, putting it right on his tail.
My analysis and proposed scenario are as follows:
The virga produced a microburst directly over Shmulik as he was waiting for the jet. He expedited his landing trying to fly out of what was likely epic sink. While his base leg was low it looked high enough to make the runway with plenty of energy to flare and roll out. But he then got hit from behind or descended into winds in excess of 40 kts and perhaps as much as 50, stalling the aircraft and removing any opportunity for control.
One of the most difficult aspects of this accident is that, given the information available to the pilot, it is hard to picture what anyone would have done differently. This truly seems like the hand of God. There is a discussion in another thread about the yellow triangle. Here is a case that would require 60 over stall speed to maintain even a narrow margin. How many people do you know that would plan to come over the numbers at 100+ on a day that is blowing steady 9 straight down the runway?
As has been noted, Shmulik was a very experienced and skilled pilot. He had more flights and time in gliders from Rifle than anyone. We all want to learn from accidents, especially what were the pilot errors we might avoid. This is a hard one to gain insight from other than this: Some atmospheric events are bigger than our plastic airplanes.
RR”
Clemens Ceipek first started to fly gliders in 1983, just after his 16th birthday. For a few years, Clemens flew fairly regularly and added certificates for winch launching and self-launch to the initial aero-tow license. Then came university, family, and a global business career. In 2017, Clemens finally decided to return to the sport that he once loved. His blog, SOARING - CHESS IN THE AIR, chronicles a second journey to become a better soaring pilot. It is, first and foremost, written for himself: to document what he learns, the mistakes, and the sense of wonder that is experienced. The blog can also serve to inspire other glider pilots and those who consider joining this wonderful, and incredibly challenging sport...