On Friday Aug. 9, a regional airline flight carrying 62 passengers and crew bound from Cascavel to Sao Paulo, Brazil crashed in a suburb of Sao Paulo, killing all on board. The crash was significant for several reasons, and not only because it was the most deadly plane accident of 2024 so far, but because it involved an ATR 72. The ATR 72 is a turboprop plane made by a consortium of French and Italian firms and intended for regional airline service. While it is too early to make any definitive statements about the cause of the crash, we can summarize what is known so far.
The flight appeared to be going normally until the plane was about eighty miles (130 km) away from the destination airport. The pilot then appeared to deviate from his intended course, and eyewitnesses on the ground reported that the plane was in a flat spin when it crashed into a residential neighborhood. Fortunately, there were no casualties on the ground, but all 62 people on board the plane were killed.
Since around 2000, the total global number of fatalities per year in commercial aircraft has been on a mostly steady decline. As total air miles traveled has increased, this means that the fatality rate per passenger-mile is declining even faster. 2023 was one of the best years to fly safety-wise, as only 102 fatalities were recorded. Unfortunately, most of that number consists of the 72 people who were killed in the crash of another ATR 72, this time in Nepal. That crash was due to human error: during the landing approach, a pilot "feathered" the propellers by mistake when he used the wrong levers in the cockpit. This turned the propellers at an angle that reduced the engine thrust to zero, and the plane stalled and crashed short of the runway.
The cause of the Sao Paulo crash is still uncertain. Along with the bodies of all 62 victims, the two flight recorders have been recovered, and Brazilian authorities are promising that initial results of the investigation will be available within 30 days.
Over its 36-year history of production, the ATR 72 has been involved in accidents resulting in about 500 fatalities. According to the Wikipedia page on the aircraft, several of these crashes have been attributed to icing conditions. Icing is a difficulty that modern aircraft are well equipped to deal with, but pilots must be aware of icing conditions in order to take steps to mitigate its adverse effects.
For example, the use of autopilots during icing conditions can lead to trouble, as one American Eagle flight was on autopilot, iced up, and crashed in the U. S. on Oct. 31, 1994 after flying a holding pattern at 8,000 feet, killing all 68 people on board, according to an AP report on the Brazilian crash. In Sao Paulo last Friday, a local meterological agency said there were severe icing conditions at the time of the accident, so it is at least a possibility that icing could have contributed to this crash as well.
Turboprop planes use jet-engine-like turbines, not for their jet-propulsion qualities, but to generate torque to turn conventional propellers. But like any air-breathing turbine, the engines of a turboprop can be compromised or incapacitated if ice builds up on the intake ports. Ice on control surfaces can prevent the maneuverability needed for proper flight, and ice gathering onto flight instrument sensors can lead to false readings and inappropriate responses from autopilot mechanisms.
Modern aircraft have ways of combating all these problems, but not automatically. De-icing systems use power and can compromise performance in other ways, so they are generally controlled by cockpit switches that the pilot must use. Preoccupation with other duties or inattention to weather conditions might render these devices useless if the pilots do not notice there is an icing problem until it is too late.
And icing can occur in any kind of surface weather. The fact that a summer thunderstorm on a blazingly-hot day can produce hail is a vivid reminder that the typical height at which the air is at freezing temperature is about 10,000 feet (3,000 meters), which commercial regional flights fly through quite often. While pilots try to avoid clouds that are likely to produce icing conditions, this is not always possible, which is why anti-icing devices are installed. But they only work if they are turned on.
It is an open question whether the ATR 72 needs attention with regard to its icing problems, but if history is any guide, a combination of icing conditions and poor crew training procedures can lead to a dangerous situation. As long as robots aren't flying planes yet, we will need highly trained professionals operating them from the cockpit, and those professionals need to pay attention to a lot of possible problems.
I recently found a used copy of Van Sickle's Modern Airmanship, 6th Edition. It is a kind of encyclopedia of flying, with all the answers to questions a student pilot could ask and many that an experienced professional needs to be reminded of from time to time. While I always knew that flying was hard, reading this book has brought home to me just how hard it can be, and how many details have to go exactly right for a smooth commercial flight to come off from takeoff to landing.
All the technical training in the world will not keep a careless pilot from making mistakes. And while pilots are human too, they hold the responsibility for dozens of human lives literally in their hands, just like a surgeon does. It takes character to live up to that responsibility, and cultivating such character is a big part of pilot training and recertification. It's possible that the Sao Paulo crash was due entirely to mechanical problems and the crew was blameless. We will have to await the results of the investigation to find out. But whatever happened, it's too late for the 62 who died. It's not too late, however, for the rest of us to learn from whatever mistakes were made, and avoid them next time.
Sources: I referred to the Associated Press articles on the crash at https://apnews.com/article/brazil-plane-crash-sao-paulo-394427322513643f4eaf517e4ac4c85e
and https://apnews.com/article/brazil-airplane-crash-deadly-voepass-sao-paulo-5c5a3371b5e899b745c1cb6e46950230. I also consulted statistics on plane crashes at https://www.airliners.net/forum/viewtopic.php?t=1490283 and the Wikipedia sites "List of accidents and incidents involving commercial aircraft," "ATR 72," and "Yeti Airlines Flight 691."
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