It's been nine months since Air France flight 447 crashed into the Atlantic, killing all 228 people on board. Still, the black boxes have not been found and we don't really know what happened. The following is what I believe happened. I will try to reconstruct what was going on on board the A330 over the Atlantic on June 1, 2009. I have no idea if what I'm posting here is correct and I am not able to explain everything. But knowing a bit about planes and aviation in general, I think I have a pretty good understanding of what contributed to this horrible crash.It was a rather calm afternoon in Rio de Janeiro on May 31, 2009. Captain Marc Dubois and his two First Officers David Robert and Pierre-Cedric Bonin started to prepare the A330-200 with the tail number F-GZCP for the 11 hours and 30 minutes flight to Paris Charles de Gaulle at around 6 pm local time. The plane was fairly new, only four and a half years old, and had gone through a major overhaul just two months before. Captain Dubois was a very experienced pilot, with more than 11,000 flight hours, more than 1,500 on the A330. He knew this plane and he knew it well. His two First Officers were in their 30s and fairly new to the A330.
Flight 447 was pretty heavy that afternoon. Dubois allowed for ten tons of cargo to be loaded into the plane plus 70 tons of kerosene. In the end, the A330 was only 240 kilograms lighter than its maximum weight. But it didn't matter. The fuel he had pumped into the Airbus was more than enough to get them to Charles de Gaulle. At 10.03 the A330 lifted into the air and headed north, north-east along the Atlantic coast of Brazil. An hour after takeoff they reached their cruising altitude of 35,000 feet. The air was a bit rough, but nothing serious so that Dubois engaged the Airbus's autopilot pretty early into the flight.
At around 1.15 am on June 1, 2009, the Airbus left the mainland of Brazil and headed towards Fernando de Noronha, an island 350 kilometers to the east of the coast of Brazil. The "fasten seat belt" signs were illuminated. Dubois knew this area well - it is feared for its strong winds, heavy turbulence and unpredictable weather conditions. They were about to enter the "Intertropical Convergence Zone" (ITCZ), an area which encircles the area around the equator. Strong thunderstorms develop in the ITCZ and clouds filled with hail and lightning pile all the way up to 15 kilometers above the sea. There is no "flying above the weather" inside the ITCZ. In the spring and early summer thunderstorms are particularly strong and common. But Dubois checked the latest weather details before take-off and kept a constant eye on the A330's weather radar.
At 1.33 am the last contact with Brazil's air control took place: AF 447 was flying through moderate turbulence, but the cockpit crew stated that the Airbus was flying at normal level (35,000 feet) at a speed of 865 km/h and that they were using airway UN873 to get to Senegal within 50 minutes. Dubois and Robert were in the cockpit, the plane still flying mostly on autopilot. They started to see supercells with thunderstorms in the distance. Those thunderstorms caused winds of up to 165 km/h that were starting to hit the Airbus. Still, the cockpit crew was not worried. The ITCZ is a nasty area to fly through, but planes do that all the time and Dubois had done it dozens of times before. If the supercells started to become too nasty, he would have to leave his assigned corridor and manually fly around them. But the weather didn't look too bad that night. Only a few bad cells were directly in the way.
In order to prepare flying around a few cells and because of worsening turbulence, Dubois disengaged the autopilot and firmly took over command of the A330 soon after they left the coast of Brazil. "Flight attendants, please take your seats!" At 1.48 am, Air France 447 left Brazilian radar surveillance. The next ten to 15 minutes were fairly bumpy, but soon after, the A330 had passed through the most severe portion of the thunderstorm area and flew into calmer skies. Dubois re-engaged the autopilot and left the cockpit to take his break (all pilots on long-haul flights take a rest at some point). First officer Bonin took over the pilot's seat. The flight attendants were allowed to move around the cabin again. Soon after, the nightmare started...
While flying through a thunderstorm and without the cockpit crew noticing, ice crystals started to form on the Airbus's pitot tubes. The pitot tubes provide planes with much-needed airspeed data, in addition to the GPS system that also offers details on the plane's speed over ground. The Airbus A330 is equipped with three pitot tubes, which are mounted at the front of the plane. At around 2.08 am, the pitot tubes started to measure different speeds. The autopilot needs consistent, exact speed data to control the plane. In this case, the computers were provided with three different speeds. Consequently, the autopilot shut down and the auto-thrust system too. The A330 was now back in the hands of the two First Officers in the cockpit. At 2.10 am the plane sent automated messages to Airbus's headquarters in Toulouse, France, that the autopilot and auto-thrust had disengaged.
The cockpit crew was now confronted with a situation they had probably never experienced before. The autopilot was dysfunctional and the plane's speed was not clear anymore. However, they could still see the speed over ground via the plane's GPS system. At that moment they had to make sure they were fast enough but not too fast either. And they needed to manually fly the plane while figuring out what was going on. Only seconds later the plane's TCAS turned into fault mode and the crew could no longer see where other planes around them were. This was the point when the cockpit crew realized that there's more going on than just inconsistent speed data. Computer after computer, monitor after monitor and system after system started to die. Soon after, the fly-by-wire computers resigned and the A330 turned from normal law into alternate law. The pilots could now fly the Airbus outside of its usual fly-by-wire limits. At that time, Air France 447 was halfway between Brazil and Senegal.
Whatever happened that night, the entire systems of the Airbus crashed. Within five minutes, AF 447 lost all systems necessary to fly the plane. The cockpit crew tried in vain to re-start the systems. They didn't work. The pilots started to realize they wouldn't make it, but kept trying. It was their only chance. The Airbus was not responding to any stick inputs. The movements of flight controls in modern airplanes are converted to electronic signals transmitted by wires (hence the term fly-by-wire), and flight control computers determine how to move the actuators at each control surface to provide the expected response. When those computers die, it renders a plane uncontrollable and that is what probably happened that night. Bonin's and Robert's only chance was restarting the systems. They tried it three times, but they wouldn't re-start (two error messages relative to restarting the systems were sent between 2.11 and 2.14 am). The plane was now flying downwards at a high speed. The pilots tried it again and YES the system restarted, the monitors started to turn on again. The computers realized they would hit the sea momentarily and lifted the nose of the Airbus up. They were only 600 meters away from the water at that point.
But it was already too late. With forces of 35 times the earth's gravity, the A330 hit the water, fuselage first. The forces were so strong that the rudder of the plane broke off, parts of the wings broke off and seat belts cut people into two parts. F-GZCP was gone. And with it 228 people. Everything happened within less than five minutes. Not even enough time for the First Officers to call the Captain back into the cockpit.
Even today it is not clear if and how the faulty pitot tubes caused the fly-by-wire system to die. Neither is it clear why the crew did not try to radio "mayday" to planes around them. Until the black boxes are found, we will not know what really caused all the systems to fail. Was this a problem that can only happen on Airbuses? Probably not, because apparently all electronics failed. A Boeing 777 cannot be steered without electronics either. However, on pretty much all older planes an accident like this one could not happen; they are still flown manually, not through electronic interfaces.
I am absolutely convinced that this problem was not caused by Airbus's fly-by-wire system itself. Something must have caused all backups to fail. However, I have no idea what this could have been...
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