Friends have been asking me about the ATR turboprop that spun into the ground in Brazil on August 9, 2024 in which 62 people were killed. Aviation Safety Network says that it was warm on the ground (17C) with a potential for “severe icing” above 12,000′ (FL120):
CNN:
It began losing altitude a minute and a half before crashing. The plane had been cruising at 17,000 feet until 1:21 p.m., when it dropped approximately 250 feet in 10 seconds. It then climbed approximately 400 feet in about eight seconds.
A spin, which is not recoverable in an airliner, is a consequence of an aerodynamic stall. In a stall, the wings lose lift because the critical angle of attack (angle between the wing and the oncoming air) is exceeded. Why does the plane spin instead of simply descending due to the loss of lift? Because the wings don’t stall to the same extent at the same time. One wing will drop first and the plane then spins in that direction. As flight instructors we are required to learn how to recover from a spin, but these techniques are useful primarily in low-performance single-engine aircraft. A Cessna 172 supposedly will come out of an incipient spin if the pilot simply removes hands and feet from the flight controls. Making an airplane this forgiving impairs cruise speed and, therefore, airliners aren’t designed with spin-recovery in mind. Instead, they prevent the pilots from the initial stall via a stick shaker and/or stick pusher that activates when the plane is getting too slow. Fly-by-wire airliners, such as the Airbus A320, prevent the pilots from stalling by ignoring inappropriate flight control inputs. (Captain Sully had the stick full back during his heroic single-pilot landing on the Hudson, just like a panicked student pilot, but the French software engineers kept the plane flying (not quite at the optimum speed for a water landing due to the higher-than-minimum vertical descent rate, but apparently close enough due to efforts of the French aeronautical engineers in overbuilding the airframe to survive both the high vertical speed and the high forward speed from landing downwind).)
The ATR 72-500 apparently has both the shaker and pusher (source):
![](https://philip.greenspun.com/blog/wp-content/uploads/2024/08/image-19.png)
Shakers and pushers prevent most stalls, but not all. A Bombardier Q400 turboprop crashed in 2009 despite the shaker and pusher activating after the pilots leveled off and forgot to add power. Wikipedia:
Following the clearance for final approach, landing gear and flaps (5°) were extended. The flight data recorder indicated that the airspeed had slowed to 145 knots (269 km/h; 167 mph).[3] The captain then called for the flaps to be increased to 15°. The airspeed continued to slow to 135 knots (250 km/h; 155 mph). Six seconds later, the aircraft’s stick shaker activated, warning of an impending stall, as the speed continued to slow to 131 knots (243 km/h; 151 mph). The captain responded by abruptly pulling back on the control column, followed by increasing thrust to 75% power, instead of lowering the nose and applying full power, which was the proper stall-recovery technique. That improper action pitched the nose up even further, increasing the gravitational load and increasing the stall speed. The stick pusher, which applies a nose-down control-column input to decrease the wing’s angle of attack after a stall,[3] activated, but the captain overrode the stick pusher and continued pulling back on the control column. The first officer retracted the flaps without consulting the captain, making recovery even more difficult.
(The root cause of the above accident, in my opinion, is the complacent attitude by the FAA and airframe manufacturers regarding deficient avionics. The aspiration seems to be an LCD version of the gauges and dials that were in a B-17 bomber over Germany in World War II. The computers on board the aircraft had all of the information that they needed to warn the crew “you can’t hold altitude at this power setting” long before they came anywhere near stalling. See my 2010 post.)
The ATR 72-500 is equipped with de-icing equipment, but no aircraft is capable of maintaining level flight indefinitely in “severe icing”. Ultimately, pilots of a sophisticated airplane will have to do what the pilot of a crummy airplane with no de-icing gear must do: allow the plane to descend while maintaining a reasonable airspeed. If it is below freezing on the surface, this means that an epic amount of runway will be consumed for landing because it will be unsafe to slow down and also probably unsafe to add flaps (the airplane certified for operations in icing conditions comes with a big book explaining what speeds and configuration to use). If the airplane can descend into above-freezing air, the ice will come off almost immediately.
Circling back to Voepass 2283, the accident airplane from yesterday, the CNN report is consistent with pilots who were trying to hold altitude rather than accept a descent: “The plane had been cruising at 17,000 feet until 1:21 p.m., when it dropped approximately 250 feet in 10 seconds. It then climbed approximately 400 feet in about eight seconds.”
The last sentence suggests that they were actively trying to get back to their assigned altitude of 17,000′. In hindsight, of course, the best course of action would have been to hold 200 knots (a good all-purpose safe speed) and descend to warmer-than-freezing air (Campinas is no higher than about 2,500′ above sea level and was 17C on the surface, suggesting that warmer-than-freezing air was available up to about 12,000′ (lapse rate of 2C per 1,000′).)
(Have I encountered icing myself, you might ask? Yes, but never “severe”. In jets and turboprops I was always able to use the onboard equipment (hot wings or rubber boots that inflate) to deal with the icing while we hunted up or down for an ice-free altitude. In little piston-powered 4-seaters that aren’t certified for known icing, the rule is that you never fly into clouds that are forecast to contain ice. However, sometimes you pick up ice that wasn’t forecast. So the rule is to descend to warmer air and, if warmer air doesn’t exist (New England in the winter), the rule is not to fly through clouds because you don’t know if you’ll be able to shed any ice. An instrument rating combined with an unpressurized non-deiced small plane isn’t a fly-on-your-own-schedule formula because you can’t get over thunderstorm lines in the summer and you can’t go through clouds in the winter due to the risk of ice.)
So… icing by itself likely cannot be the cause of the recent accident in Brazil.
The escape sounds unintuitive since they were in a thunderstorm, the autopilot would have put it severely out of trim & then disengaged. The instinctive response would have been to pull up & slow down. Icing has been a big deal this summer. It seems wherever there’s a thunderstorm, a falling Palatus PC-12 or ATR 72 is soon to follow.
What’s your source for this flight being in a thunderstorm? Generally both ATC and pilots try to avoid thunderstorms. U.S. ATC has ground-based weather RADAR images on their scopes so I think the Brazilians would have it as well. Airliners have weather RADAR in their noses so that pilots can avoid thunderstorms with real-time information about the location of heavy rain. NOAA says “Severe icing is likely to occur in the upper half of heavy cumulus clouds approaching the mature cumulonimbus stage” (i.e., getting ready to rain, but not raining yet) https://www.weather.gov/source/zhu/ZHU_Training_Page/icing_stuff/icing/icing.htm
Flew the ATR-42 & ATR-72 in the late 1990s for a regional airline in the Midwest of the USA. The stall recovery training in the simulator was all technique and not much as ‘instinctive’ as in other aircraft I’ve flown before. There was a military pilot in my initial class that could not face this and had to quit with a great deal of frustration. So these aircraft and the required training is okay for most but not all pilots. We were shown all the videos and further testing and modifications made to the ATRs after the American Eagle 4184 accident. We were told that the aircraft could now better handle icing conditions. However, experienced captains (that I flew with as an FO) handled icing conditions as an emergency in ANY kind of icing conditions. The best part of it was the that we handled this expeditiously, counting on ATC to issue immediate clearances for lower altitudes. ATC understood that without the immediate clearance we were going to declare an emergency ‘immediately’ and deviate from assigned altitude, anyway… so we worked together on this (and I’m sure we all avoided the possibility of a disaster and at least the required time consuming reports and paperwork.)
One last experience that I will never forget, after modifications were in place, was while waiting for our plane in the crew lounge, an ATR crew came in (Captain & FO) clearly stressed and looking pale like ghosts… they just cheated death. They explained to all in the crew lounge that weather conditions were down to bare minimums on the ILS, and that while descending past the FAF they began losing the GS while AT FULL POWER because of icing. The the GS pegged above and they ‘stabilized’ about 200 feet above the ground without further descent until the GS reappeared… and right at GS intercept they saw the runway and landed. They were lucky to be alive.
People. These ATRs belong in the tropics (where American Eagle end up sending most of their ATR fleet, TJSJ.) I’m retired now and been able to finish a successful and uneventful major airline career as a captain while flying the Airbus. Captains should not think twice and exercise their emergency authority especially where the flight capabilities of a the aircraft could be in jeopardy. FOs, you need to remember to stand strong when you see your captain not following SOPs (extremely difficult, but I’ve been there… and was successful… had a captain attempting to depart without considering the required deicing… best thing to do is don’t fight it alone… I asked ground personnel to come to the cockpit and tell the captain “sir! you have ice on the wings!” At this point the captain had to comply with de-icing; however, he didn’t talk to me for the remainder of the 3 day trip. So what? I performed my duties and was proud of it.) So FOs, don’t let you guard down! It is an art more than a science to be the good chameleon you need to be. You will become a good psychologist for your future FOs and crew. Your experience will be much more than controls, stick, rudder, knobs and levers. Embrace it and make the most of it. CRM is crucial, the crew concept (even with flight attendants) is also crucial. Also, a few airlines today are being forceful regarding fatigue calls, stand your ground, don’t let anyone force you to fly fatigued. Anyway, I deviated a bit from the subject at hand but couldn’t resist to bring my 2 cents on issues that I find today as concerning in this day and age. Magnar’s Voepass video posted here is magnificent, and agree on his statement that much more needs to be investigated and data remains to be seen for a full and comprehensive understanding of this accident. Best luck to all.
The videos I have seen (the plane fell relatively slowly from high altitude so many people were able to film its demise) seem to show the engines at power. I believe the first step in the spin recovery procedure is to reduce power to idle. Icing seems to be the most probable cause, but perhaps some event in the cockpit could also be what caused the spin.
As far as I know, icing can’t cause a spin. It will degrade your airplane. But as the F-4 pilots said in Vietnam “with even power even a brick can fly.” An airliner doesn’t have a lot of engine power relative to its weight, but if it is at 17,000′ it has plenty of potential energy that can power continued flight (you tap into that potential energy by descending).
“Relatively slowly” was however almost 200mph (17000ft/min).
Perhaps icing cannot cause a flat spin, but it can provoke a loss of control that results in one. I have been an an instrument-rated pilot (I also fly gliders) for decades, but I’m far from being an expert on aviation matters. If the accident airplane encountered supercooled water droplets things could have turned bad very fast. Time (and real experts) will tell.
A good video, in my opinion.
According to Reddit, the pilot requested descent from ATC without using the word “emergency” and was denied. Also the at least one of the props in the video sounds feathered meaning the pilot might have been trying to correct the spin and/or an engine was malfunctioning.
Videos:
https://x.com/hubertmelin/status/1821955262296522895?t=Es1X08KyiOG9tL7JJ98zBg
It looks like he almost catches it at one point, with the nose pointing downward. I guess those small control surfaces don’t have that much bite