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Puckinflight

An all things aviation blog

On June 1, 2009 Air France flight 447 from Rio to Paris fell from the sky over the Atlantic Ocean killing all 228 passengers and crew. Today July, 5th 2012, the final report on the accident was released by the BEA the French aviation authority. This report containing numerous recommendations represents the final word on what happened.

What happened? Well if you have seen the Nova film on the matter, then you have a good idea. If you haven’t you should. I’ll do my best to explain.

Cruise flight in a modern aircraft occurs at high altitude. Makes sense the higher the altitude the less air, the easier it is to move the aircraft through space. The downside is the aircraft has to be going fast enough to move enough air over the wings to generate lift.

Thus, infinite speed infinite altitude right? No.

At those speeds going though air is like going through soup. The aircraft causes disruptions in air. Too fast and these disruptions break the flow of air over the wings causing a high speed stall. Too slow, it stalls, too fast it stalls. The speed in-between is called the coffin corner. 20-30 knts either way at altitude and the aircraft stalls.

How do you measure speed. Well, at cruise flight speed is a function of pressure. The aircraft needs to know how much pressure is pushing against the front of the aircraft. They use pitot tubes. The measure pressure.

In this case the pitot tubes iced over. Thus the aircraft was unable measure pressure. So AF447’s electronic brain concluded that the pilot should fly the plane.

Ok, so if you don’t know the speed, you eventually stall and then you die.

No. If that were true there would be a lot fewer planes around. Airbus built in a setting where the aircraft will be airworthy. 85% power and 5 degrees nose up and the pilots will be able to control the aircraft.

If this is true why did AF447 crash? Well the pilots didn’t fly the aircraft. Imagine this.

You’re a commercial pilot, you’re 3hrs in to a 10hr flight. The flight is going smoothly, systems seem ok, dinner was just finished, and through a combination of food, stability, and slight tiredness, you’re not as alert. You know the majority of incidents happen on takeoff and landing, so there is not much to worry about. Oh and it is pitch black outside and inside. Then all hell breaks lose. Lights are now flashing on the control panels, audio alarms are going off proclaiming multiple emergencies, and you have no idea why all of this is happening.

The purpose of these alarms were to draw the attention of the pilot. The pilots of AF447 were both fairly junior. The senior pilot was having a rest. This is standard procedure for all international airlines. However, here the situation went from fine to catastrophic in a matter of seconds. The pilots did what anyone would do, panic.

Panic is something good airline crews plan for. It’s called crew resource management. Step one of the plan is secure oxygen. Step two is fly the plane. Step three is assess the situation. Step four is take appropriate steps to remedy the problem. Granted this is an over-simplification but it works here.

The crew on AF447 didn’t fly the plane. They got so caught up in alarms, systems, and other things, they panicked and forgot how to fly the plane. Nova showed what to do, set power and trim, fly the plane, then listen to the alarms.

Wait listen to the alarms is last? Yup, the pilots have to fly the plane. But the pilots are not all to blame here. (Though I think they are ultimately responsible)

Airbus shares a lot of the blame. People talk about the pitot tubes and that it was a parts failure. I call bull on this. Planes are designed to fly after an engine explodes, a pitot tube failure should not bring down a Cessna 152 (Do Cessna 152s have pitot tubes?) much less an Airbus 330.

Let’s take an engine explosion. Qantas Airbus 380 flight from Singapore to Sydney had an engine compressor explosion after leaving Singapore. Plane returns safely to Singapore, no fatalities. In documentary about this flight one comment the pilot made interested me a great deal. He mentioned having to go through an acknowledge pages of alarms on his data screen as well as the rest of his control panel. He stated that he spent a lot of the emergency not dealing with the emergency but acknowledging that there was a problem. As if he didn’t know from the engine explosion.

I think Airbus is overloading pilots in emergencies. Rather then encouraging the pilot to focus on flying the plane they are providing the pilot with too much information about the situation. I want my pilot flying the plane, no acknowledging a system prompt in the first few moments of the emergency.

Where the line is between too much and too little information, nobody knows. However, with fewer alarms would the AF pilots been able to save the flight, I think so.

Whatever happens now and in the future this sad chapter in aviation history closed.

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