Brazilian ATR 72 Crash Cause 

I happen to live some 18 miles from the accident site. The ATR72 was performing a Standard Arrival (STAR) into Sao Paulo's Guarulhos airport (the accident happened inside Sao Paulo TMA (Terminal Area). During the couple of hours before the accident, several crews reported severe icing throughout the whole region. The ATR has deice boots. Turboprop engines such as the Pratt & Whitney PW series can not afford to provide the amount of bleed air required for hot air anti-ice systems. The ATR wing uses a 5-digit modified NACA airfoil ranging from 43018 to 43013. This airfoil seems to be very bad at handling SLD (Supercooled Large Droplets) icing. If ice accretion becomes asymmetric, the asymmetric drag will cause the aircraft to yaw, which, combined with a stall, results in a spin.

theres a reason ATR pilots in chicago refused to fly them in the winter. theyve had the icing issues since the 1980s!

Mate that was by far the best vid I've ever watched on RU-vid, absolutely brilliant how well you explained that, I have a basic knowledge of aviation and they way you broke it down was excellent !

Excellent and thorough presentation. One additional detail, after the ATR72 American Eagle crash in 1994, we tested an ATR72 out at Edwards AFB, CA, using our icing testbed KC-135. The air refueling boom had a misting spray ring, which sprayed colored water on the leading edge of the ATR72 one wing at a time (to retain primary flight controls of the ATR72). We photographed an “ice fence” build up 2”-4” tall directly in front of the aileron hinge. This ice fence acted as a spoiler, destroying laminar airflow over the aileron (and rendering that aileron useless). For safety, the ATR only “lost” one aileron during these tests, as the other wing was always in clean, dry air. Had both wings been subjected to this ice fence buildup, the aircraft would have lost all roll control and spun in. All major ATR72 operators moved their aircraft to warmer climes to avoid this risk.

The US has stricter rules against flying the ATR 72 in these conditions due to American Eagle Flight 4184 that crashed in 1994. Not to be overly dramatic, but these rules are written in the blood of 68 Americans. That means this problem was more or less resolved THIRTY years ago. It’s a shame other countries seemingly don’t take them as seriously.

Why this flight was allowed to fly into known icing conditions published in the SIGMET is unfathomable. Blame will go to the airlines flight dispatchers and the pilot that flew into known icing.

Dude it's awesome to see the face behind the voice. Thank you for making these videos. We are all pilots. Fascinating stuff.

Thanks for the detailed explanation but all I can think of is the terrifying ride to the ground for all on board. My wife told me some people missed boarding this flight because they were late getting to the gate. As for the souls on board, RIP.

I wouldn't fly on an ATR. They are too susceptible to icing.

Severe icing, known (as in reported) or forecast would disallow for dispatch of a flight here in the US.

I'll just say this as a r/c patter, 3-D, heli pilot for 35 years and full scale rotary and fixed wing as an adult today (not commercial.. Personal). I don't think I've ever seen a scale airplane somewhat similarly spec'd go that flat... Easy to do with other airframes but that was scary impressive.. I don't mean impressive like I'm happy.. It is SCARY as heck to watch and know how long it took to come all the way down with them cycling the throttles trying to get out, at least lower down.. Like a lot of people.. FL170 is a bad place to be for icing... I hope they don't sit on the FDR too long.. Not that I'm into listening to aviators freak out but as someone who has always studied crash or death / injury investigations in things I do... The CVR too.. Well, transcript.. RIP to all..

Best explanation of stalls and spins I’ve seen. As an ex Navy spin instructor, I will say I’m impressed. I will also say when I switched from military to commercial, I was amazed that the cockpits didn’t have AOA indicators because any fighter pilot will tell you it’s all about Angle of Attack. You can stall at 300 IAS if you pull enough Gs. I will also add how surprised I am at the civilian community and how little emphasis there is on spins and how far it is in their training they they even practice them. CFI I believe?

Just to add something to your otherwise very correct video. The analysis of the tragic AF447 accident showed also some overconfidence in Airbus philosophies that the aircraft will "take care of everything" as their CEO at that time stated, "even my cleaning lady could fly this A/C". Resulting that there was no training provided for pilots to to recover a Loss of instruments event in HIGH ALTITUDE, they trained it only for situations after Take Off. The problem with these A330 pitot-systems was detected before this accident happened, there were some incidents with it where the crews just did the right thing. The A330 fleet had to change these sensors to another type, the accident aircraft were still to change the sensors. To my mind there is way too much trust in automated systems (= less costly simulator training) and less training for Pitch & Power, especially at higher altitudes.

Great and detailed explanation. Sorry to all the families that lost their loved ones.

Autopilot in alt hold will try and maintain height in icing conditions by raising the nose and slowing down , the wing with ice can’t maintain lift and stalls any yaw will result in a spin. This could have been insidious and the pilots didn’t notice until the stall warning and spin. Real shame so sorry for everyone involved.

i've flown the ATR72 for many years as a first officer than captain than as an instructor . we practiced a lot the exercise of stall recovery in the simulator and the ATR has many protection " stick shaker and pusher" , it's hard to get it in a flat spin . the only thing it comes in to my mind is LOWPITCH in Flight it's a vitious failure if not treated quickly . you can get in a spin , it resembles a flat spin . i'm really looking for the result of the investigation .

Why ATR engineers aren't yet able to get rid of this imperfections for almost 30 years? The technology has advanced so much.

Best there is explaining technical details. Thank you, sir!

don't fly in icing with auto pilot on. learned this lesson early on in my flying

The ATR is notorious as a flying coffin any time it encounters icing conditions

They've had this issue with control surfaces icing up since the 90s. It's really a shame.

Greetings from Jundiaí, Brazil. It's very sad to witness this. I live near the crash site and I've seen fire brigade trucks rushing to where the plane crashed. Now, there must be respect for the victims, their families, friends, there should be patience to solve this investigation and vultures, the press and lawyers should be away from this and not to prey on or exploit families.

I remember at least one crash of an ATR in US, the plane just dived into the ground, the NTSB suspect ice formed in front of the ailerons ? The French insist there is nothing wrong with their plane.

As soon as I found out it was an ATR I knew it was their lousy de-icing boots…

Icing was my first thought. About 25 years ago, the ATR brand was badly tarnished by a crash caused by icing. The ice extended rearward beyond the boot, making it impossible for the boot to remove it when activated. I haven't kept up with it, but I thought that the other operators avoided known icing with the remaining fleet, and I am not certain whether the boot system was ever redesigned to accommodate the icing problem.

100% agree in this analogy when I first seen the video i flash backed to air france and the ATR american crash where icing was suspected and led to recommendation of the deicing system on all atr craft. I seen the weather in the area first thought was unreliable airspeed due to severe icing which is a notorious issue to turbo prop high wing aircraft.the fact it got into a flat spin is incredibly rare. the power reduction on some of the videos is noticeable to attempt to recover but was too late to change the outcome.. the horrific ordeal these passengers and crew endured is unbelievably sad. 😢

Thank you for the detailed explanation of what apparently happened and how it probably happened.

I don’t understand how the ATR 72 could even be certified all these years with all these icing conditions happening numerous incidents

There was another atr 72 down due to icing problems in Cuba in 2010, something is wrong with this system

Super interesting. Thanks for the video and RIP to all the victims.

I'm amazed at your concise and thorough explanation of flight aerodynamics which you made understandable even for a layman like me. Excellent job.

Always appreciate your videos, but I gotta do an obligatory "um, akchually......" The "equal-transit theory" around the 3:00 mark is a common incorrect explanation for how wings lift. Two neighboring air particles that split at the leading edge are not forced to come back together at the trailing edge. Plenty of wind tunnel tests show this. The general Newton 3rd Law summary between 2:40 and 3:00 is spot on - the wing pushes air downward with a force that matches the aircraft weight, letting you "float" in the current. And for the scope and audience of this video, that's the best quick-and-easy explanation we can do. The bit about the wing's curvature making the upper air mass travel faster than the lower is also perfectly correct, but the simple reason is...that's just the nature of air flowing around a wing. The lesson's complexity spikes VERY quickly beyond that (very basic) level of detail.

Cutting severely between angles on this host put me into a flat spin. Dude. Stop.

I think what happened is tragic. If grounding the Boeing 737 Max by the FAA, EASA and many other governing bodies around world was the correct. The FAA might do the same thing with the ATR 72. ATR needs to make their planes less susceptible to severe icing.

Dude..... Where have you been? I'm glad we have two videos from you in recent weeks, but man, that's not enough. You're too good of an articulator to not grace the YT aviation universe with your take on things.

I’m theory, had every passenger rushed to the front of the cabin, might there be a chance that the aircraft fell into a nose-down attitude and thus recovered?

Super thorough video. Also appreciate all the commentary from other fellow pilots. What I also appreciate about you the narrator is how articulate and to the point you are. So many videos are extremely frustrating and painful to listen to, this one was easy. Not a fan of the ATR either way. Those poor soles. What a tragedy. We all try our best to mitigate risk in this business and sometimes the equipment lets us down, sometime we let ourselves down and sometimes it’s both in addition to Mother Nature. Hopefully we can get to the bottom of this sooner rather than later for everyone’s sake.

Well explained and well spoken too. As an ex RAAF aircraft tech I enjoyed your video and the way you explained the pitot system and aerodynamics. Thanks.

Extremely clear - I subscribed right away. A throughout and detailed explanation of how lift, stall, airflow, CG, airspeed (measured via pitot tubes) etc. work - all concepts I knew about decently well already, but that I rarely found explained so well. I’ll be in for other videos too. Quick question: isn’t the “T-tail” (typical of the ATR family) in any way to be considered a culprit, too? I read in the past that this particular tail configuration is prone to deep stall / super stall outcomes (impossible to recover even when they are flat stalls). I don’t find it mentioned anywhere (also in other analyses), but that’s probably because all the rest (ice, plane attitude, inability to prevent the stall in the first place) are already explaining what happened more than enough…

That was an amazingly educational video. RIP to all those that perished. Such a tragedy.

Don't discount failure of secondary low pitch stop on one of the engines. Not discounting ice. But if left engine failed and wouldn't autofeather. Bad situation!

Very good explanation for people like me who do not know much about flying or avionics. The resulting hypothesis and the rationale behind it was superb. Thanks so much

ATR is a good aircraft but it has issues with icing.

Thanks for an easy to understand explanation of why the plane fell from the sky.

The equal transit theory of lift has been debunked many times. There’s no reason to believe the same air molecules converge at the trailing edge, thus causing higher velocity and lower pressure. We now attribute lift purely to the “flinging of air.” You won’t hear about equal transit in any modern description of lift, unless it’s to mention it’s just not true. Google equal transit theory and you’ll see what NASA has to say about it.

What a video!!! So much technical explanations on a easy way to understand

I think it's fair to say GMT is no longer the current vernacular; UTC is the time standard used in aviation for flight plans and air traffic control and is what most people use here in Europe anyway. Greenwich Mean Time (pronounced Gren itch), is a bit of a blast from the past of naval square rigged ships etc, calculating their longitude position using a clock set to GMT. RIP to the passengers and crew and a good insight, thank you.

Excellent teacher

I'm not sure unreliable airspeed is all that likely to have happened. To my knowledge, there have been 4 previous ATR crashes involving in flight icing, and only one had any unreliable airspeed. The wings of the ATR are particularly sensitive to ice and the deice boots are considered by some to be undersized. It doesn't matter if the airspeed is accurate or not; when the wings stop working, you stop flying.

Take home message: don't enter a spin with a commercial plane.

3:05 Love your videos but you just cited a widely debunked myth about lift here. What you’ve described here is known as the Equal Transit Theory of lift. Google it and you’ll see that both NASA and MIT (among others) have taken the time to explain that this theory is scientifically incorrect. It is widely believed by flight instructors for one reason or another. But they are wrong.

Refer to the US NTSB report on the ATR accident over Chicago a few years back. It seemed there had been a few crashes like this one caused by icing on the wings. The NTSB found an icing problem on the wing and in previous accidents the pilot was blamed but it was the wing ,NOT the pilot.

I've been on some half empty ATRs where they have had to rearrange all the passengers for balance.

I remember Chuck Yeager saying about one of his test aircraft "I couldn't recover from a flat spin, but I could recover from an inverted flat spin". This depends upon getting the verticle stabilizer into the air stream, I don't know if a high T tail would recover, but it's a good question to ask.

I know that this is rare, but I wonder if a tail cone chute could stop the spin. We had this for flight test on the C-17 aircraft.

The second ATR to go down in not so many months...

In Ernest K Gann's book, Fate is the Hunter, he describes an incident when as co-pilot in a DC-2, they encountered extreme icing. Gann's captain was able to divert and land safely but they were fortunate to survive. IIRC it took mechanics a long time to de-ice the DC-2. Gann said that the DC-2 handled ice better than a DC-3. He also despised the C-87 (Liberator) because of its inability to deal with ice that a DC-2 or DC-3 would have been able to handle without a problem.

Very good video. Informative in a straightforward manner. Thank you for referring to the pilots as captain and first officer. Not captain and copilot.

Grest Production, great info. This channel can blow up. Keep rolling!

Another classic. Thank you from Australia…

⁠happened in cuba a few years ago… ATR … they requested atc to decend for icing but there was another plane at that altitute so they waited a few minutes … the plane crashed short after you AERO CARIBBEAN FLIGHT 883 you can watch the simulations on youtube

These damn ATRs are obviously lethal in icing conditions. Most other turboprops handle it much better. I can’t believe they flew right through the middle of the predicted icing levels.

Either anti icing equipment failed or the pilots failed

Great and thorough assessment. Your theory is highly probable however I wouldn’t say that aircraft rarely get slow during the decent phase of flight. I imagine it is just as likely as any other phase and was the result of Colgan 3407 crash. These aircraft with autopilot and no auto throttle are obviously more susceptible. In this case it’s probably unlikely because I don’t believe there was an intermediate level off.

I live 11km from the accident site, it was a freezing day with light rain, an unusual cold that is only getting better today! The pilots probably didn't expect this, as we are in a tropical country, climate change is here, aviation needs to be prepared, if that is possible.

I’ve flown ATR’s in Southeast Alaska, where you can’t get any more severe icing than that and without any problem. I’m sure the pilots could’ve been trained better to deal with this….

It seems that ATR's wing was made for performance to the detriment of the ice accumulation resistance, in conjunction to an inadequate boot deicing system.

It may have been a repeat of AE4184 involving rollback ice resulting in hinge moment reversal of the ailerons, disconnect of the autopilot following with a departure from controlled flight, vs. erroneous airspeed and traditional stall/spin.

Hey just so you know. GMT is used for all navigational vehicles and purpose because it's the zero hour on the clock and it is known by that all around the world. That way reports and vital navigational information can be used and passed with a common time format. Military, civilian, every country agrees to use it. It's existed for eons.

As soon as I saw the video I thought it was a CofG related incident. I was in a similar aircraft in the Caribbean years ago where an inexperienced and uneducated local air hostess organized all passengers to the rear of the aircraft for her convenience. Being a pilot I insisted on talking to the pilot and we repositioned the passengers thereafter much to her chagrin and indignation! Good analysis video about a tragedy!

oh please ... don't use that horrible and inaccurate "distance travelled" explanation for lift. At a simplistic level, it should be enough to say lift is suction above the wing and a bit of pressure from below. curvature is more efficient than thickness distribution (wing section) ? extreme curvature (flaps and slats) produces a lot of drag for the extra lift. But why go this way ? wings develop lift by two means, one is AoA which also increases drag; the other is speed. So a plane will cruise at a low AoA for minimum drag but at a high speed, come to landing (and take-off) the plane needs to be slow (so runways are as short as possible). slow the plane down, compensate with AoA and curvature (flaps and slats). The pilot (or the auto-pilot) is controlling the plane's thrust, AoA (using the elevator via the control column) to achieve the flight path (level flight, climb, descent) he (it) wants. stall ?? in normal conditions the airflow is "attached", streaming smoothly along the upper surface of the wing. as the AoA increases the airflow has to "work" harder to stay attached, and at some stage it will suddenly "detach" (or separate) from the wing causing a "precipitous loss of lift". The usual solution for a stall is to reduce the AoA, push the stick forward, and this usually takes altitude to recover. In this case they probably had the altitude, but something else went wrong. Maybe as the AoA increased the airflow, the "wake", streaming aft of the wing, covered the tailplane (and the elevator) which is critical for stability (and pitch attitude, AoA) and the pilots lost the ability to control the plane's AoA, and the plane fell out of the sky with little forward speed (as shown in the videos). stall speed vs stall AoA ... really ? a stall is an aerodynamic condition when the AoA is too high for the speed (or the speed too low for the AoA). We use speed these days 'cause that's the easy to measure instrument in the cockpit. Gone are the days of an angular indication for speed (rather than the universal pitot system). as an engineer with his "sliderule" (good lord, do you really think we use them these days ??!!) ... an engineer with his computer would be WAY more accurate. I assume you fly planes that don't have stall protection systems ? 'cause that's the primary safety mechanism (AFAIK). But these don't work to protect against icing, which is why pilots need to turn the anti-icing systems on in icing conditions (and there can be cockpit instruments or visual cues to indicate icing conditions). Deicing boots like turboprops have mess the airflow and can't be inflated all the time. De-icing boots work well (as nearly 100 years of flight testifies) ... sure they are not perfect and need to be well designed and ATR's anti-icing systems has caused crashes in the past (as the ice accumulates just aft of the boot, possibly because of the laminar flow wing). icing + ATR42/72 is probably not good., probably because of the laminar flow wing.

i was on a very casual one third full twin turbo prop in NZ and one of the pilots coming back and asked us to spread out around the cabin to trim the aircraft.

ADR 72 has the worst possible reputation

Great info. I watch a ton of crash videos so I'm familiar with some of the basics but I've learned a ton from this.

I'm wondering if having the throttles at idle would have made much of a difference. With the engines reved up, and the aircraft yawing to the left, the gyroscopic precession of the props, (I don't know about the turbins, if they spin the same direction as the props) would have caused a nose up force. In my opinion, the aircraft wasn't rotating fast enough around a vertical axis to explain its almost flat attitude.

That was the best explanation I have ever heard. I understand stalls but I will save this to show people who don't understand what happens. Thanks

I remember an accident in the alps with an ATR where the aircraft flew into icing conditions but with the anti icing system off. When the pilots noticed this and turned it on then the ice was disodged but slippped back across the wing and lodged jamming the ailerons thus causing a loss of control. Just a thought but we will have to wait for the aircraft accident investigators report. The French BEE are extremey thorough so together with the Brazilian authorities the investigation is in good hands.

Didn't this same thing happen in the US in the 90s which led to a big hubbub about this particular plane's ability to handle ice? I sorta recall in this incident the plane went into a spin too, the pilots very nearly recovered from the spin but the tail got torn off in the process. I might be mixing up incidents, it's been a awhile seen I've read about this.

Why is it that there are no readily available releases or discussion of the communication's from the plane to any control? Surely during the time of the emergency there was.

Great video. If i turn the sound down it looks like golf commentary from the masters in georgia. Lovely sky.

Severe icing and autopilot not turned off. It's that simple, the pilots would have been fighting the automated systems that are designed to save the aircraft

It's not yet confirmed that icing was the main cause of that accident, since the accident happened so recent, and the official investigation is still undergoing, it's too early to say it was just mere icing. The ice itself, when isolated does not necessarily cause a stall and then a crash. It surely does have an effect on aerodynamics, but when in combination with other factors that still needs to be investigated as well, such as probable pilot error, incorrect flight informations, and even engine failure, ice didn't cause the crash.

I love the Third Law explanation of wing function!!

Who is he talking to at 0:25?

Bravo! Well said. I enjoyed listening. Icing and an aft center of gravity… I like the ATR line. I use to fly the Q400. I love flying the aircraft as well. The only problem with it was you had a 24,000 foot ceiling that made you hang out in the weather, which gave you a bumpy ride. Initially designed on a napkin and built for Canadian winter. The boots on the forward wing were very pronounced. I could easily shed ice. This was great for a turbo prop

I dont believe this was JUST icing not the way it just dropped like a rock with a ground speed of around 26knots. I'll be surprised if it is just that.

A eyewitness on the ground said that she heard a loud noise and went to look out of the window. It was then when she saw the plane staling.

This crash reminds me a lot of Aero Carribean Flight 883. It also encountered icing, stalled and entered a flat spin just like this plane did. You can find an animation of the crash on youtube easily.

Thank you for your hard work. May I note a couple of things? My eye seems to note a difference in the color of your shirt, from the straight view, transitioning to the side view. It harms nothing, but it was noticable to my tired eyes. Your introduction was good. Thankfully, you had no loud obnoxious music to start the session. Plus it was brief and peaceful. Like others said, you are good on aircraft technicals. I know some like a brief ending, and I respect that. However, from someone only listening, not strictly watching the screen, the ending was so quick, I didn't detect it coming. But your style is whatever YOU want it to be! I don't know your plans, but if it involves rapid channel growth, you might consider someone to help with editing, who could focus on branding, sounds, and production of the video flow. That would free you to grow the amazing quality of your content. Compared to some, I think you have much too much knowledge for your current subscriber level. Growth potential for you is easily there, if you want it. Looking forward to more...

"for whatever reason"....ignorance is no excuse.

it's the first time I hear stall is due to angle of attack and not "speed", outside of a book. So refreshing. Not that the "stall speed" is necessarily wrong, but that is speed maintaining level flight and the slower you go the higher the angle of attack. A wind shear, a bank angle or a sudden yoke movement can easily provoke a stall at speeds (much) higher than the said stall speed. Licenced pilots should sometimes refresh their theory

5:03 Slide Rules? What century are we in, LOL? Haven't heard that term for many years, I bet none of my grandkids have EVER heard it!

A good indications on the ATR are when you see thick Ice running back on the side windows, you know that you are in trouble and you are in sever icing condition and you need to descent fast and keep maximum speed to prevent any stalls . I flew the ATR in Scandinavian, in the freezing cold, snow and lots of ice and the aircraft performed well . but again always on the lookout for that dreadful snow and ice . I flew the Short in those conditions as well and that was more like sailing an over iced fishing boot than flying ( Scarry as Hell )

My lay opinion is that the shape and proximity of the propeller blades has a lot to do with the accident. I have a fan of this type and in strong crosswinds it oscillates and falls if poorly supported.

It's important to understand that icing categories depend on the aircraft type as they relate to how a particular aircraft type copes with icing. So what may be "light" icing to one aircraft type may be "severe" to another. But if anti-icing and de-icing equipment is not maintained, tested and used exactly as intended, an aircraft that may be normally able to cope with "moderate" icing may in fact be unable to do so - which by definition turns "moderate" icing into "severe". This has been the cause of many icing accidents, for example Roselawn in 1993 - another ATR 72.

Thanks for the thoughtful discussion and information. The confusing avionic information and your explanation of its relation to possible icing was very helpful. By the way it's "Grennitch". Greenwich is pronounced "Grennitch"

WWII history in the CBI, flying the Hump on dangerous missions I recall pilot Earnest Gann saying about the B24 cargo variant that its wings "couldn't carry enough ice to chill a highball." The chord on those C-87/B24's wings were much skinnier compared to contemporary WW2 AC, much like the ATR.

Nicely composed explanation. You have an easy delivery style to listen to. Thank you for the presentation and heartfelt condolences to the families of the lost ones.

I still believe that unusual air speed discrepancy has something to tell...

I’m waiting for the air crash investigation to conclude before making any suppositions