The Tragedy of Air France Flight 447

I’ve been following this accident from the beginning, including speculating on the cause in my post What Happened to Air France 447. My theory about the accident was that the plane ran into severe weather and, as a result, most likely suffered an airframe malfunction. And until the black boxes were found that’s really all anyone could do – speculate. Now we know exactly what happened. And the saddest part about it is that this is one accident that didn’t have to happen. There was nothing aerodynamically or mechanically wrong with the aircraft when it crashed into the Atlantic in June of 2009.

As with all accidents, there are lessons that can be learned that help in preventing similar accidents from occurring. That is the case with this accident. Second guessing the flight crew doesn’t accomplish anything. Had I been confronted with the very same scenario I hope I would have responded differently, but I wasn’t there so I can’t say with any certainty how I would have handled the initial problems that cascaded into the accident. The truth is human beings make mistakes. I make mistakes. The system works because there are multiple layers involved to help catch mistakes before they can combine into an error chain that results in an accident.

This accident was the result of a combination of human errors, weather, automation, and inexperience. I haven’t read the official accident report. I have read much of the cockpit transcripts. My conclusion is that this accident is a textbook case of an unbroken error chain. It starts with an improper setting of the radar tilt. For reasons unknown, it appears that the radar antennae wasn’t set correctly, and the crew did not see the sever weather ahead of them until it was too late. Other aircraft in the area chose to deviate around the weather.

Not being aware that severe weather lay ahead (a failure by the crew as well as the unavailability of better weather information), the captain went in back for his crew rest. He was replaced in the left seat by the relief pilot. Within minutes the two pilots remaining in the cockpit became aware of the bad weather ahead. They called the flight attendants and told them to prepare for a rough ride. I’m not sure if a similar warning was given to the passengers.

The plane entered the tops of a line of severe weather and instantly was met with turbulence and super cooled water droplets that over taxed the electrically heated pitot tubes, something I was unaware was even possible. Anyone who has ever accidentally touched a heated pitot tube can tell you that conditions would have to be extreme for them to ever become clogged by ice. But that’s what happened.

The fly-by-wire Airbus 330, without the proper airspeed information, instantly began giving the crew multiple failure warnings. In training, pilots are never given more than one emergency at a time. So the multiple failures combined with the rough ride made the process of analyzing the cause much more difficult.

The relief pilot instinctively pulled back on the sidestick and the plane began a dangerous, rapid climb. The airspeed bled off and the plane entered a stall. But the nose of the aircraft never fell through the horizon as it would typically do in a stall. Instead it remained in a nose high attitude as the plane began loosing altitude at up to 10,000 feet a minute. The two pilots were confused as to what exactly was happening. The first officer called in back to have the captain return to the cockpit. When the captain got back to the cockpit, he took the seat behind the two pilots at the controls and he too then tried to analyze what was happening. The first officer can be heard saying, “I don’t understand what’s happening.”

At some point the pitot tubes were cleared of the ice buildup and they started working properly. The first officer eventually tried to take control of the aircraft from the relief pilot. The relief pilot relented, but soon after again grabbed the sidestick and began pulling it full aft again. If both pilots are operating their sidesticks at the same time, the computers average the input. So the result was the first officer’s attempt to lower the nose, the correct action, was hampered by the relief pilot’s actions.

Meanwhile the passengers in back had no idea what was about to happen. They may have been concerned with the bumpy ride. They may have noticed the plane was descending. But with no communication from the cockpit and no visual cues outside, they were most likely unaware of the impending contact with the water.

If any one of the links in this error chain had been broken, the accident would not have happened. Had they saw the weather earlier they would have deviated, had the captain delayed his crew rest he would have been at the controls, had the pitot tubes not become clogged they would have experienced nothing more than a rough ride, had the aircraft had a conventional yoke as opposed to a sidestick it would have been more apparent what the correct corrective action should have been, had the relief pilot simply let go of the sidestick they would have been able to recover from the stall.

This is one accident that hopefully will never happen again.

Update:

The comments I made about the radar antennae being set improperly were incorrect. Please see my review of the book the Rio/Paris crash for a more detailed account.

 

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