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Old 9th Jun 2011, 13:37
  #1543 (permalink)  
sd666
 
Join Date: Apr 2011
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Exclamation Quit the Airbus bashing, puhlease.

OK. So this thread again degenerates into Airbus bashing. No surprise there then.

Let's just step back a minute and consider the frequent calls to ditch all that fancy automation and put full authority back into the hands of a human pilot.

Consider what the objective of the Airbus laws are - from first principals.

They allow a pilot to control the aircraft with maximum performance when the muck hits the fan. Prevent a stall, keep the aircraft flying, even on the brink of maximum AoA. Prevent overloading the airframe. Prevent overspeed. If you are faced with looming CFIT, pull back, all the way, and the Airbus will deliver maximum performance to avoid it.

Case in point: The Hudson river incident. The media loves a hero pilot, but by rights they should have been equally applauding a bunch of anonymous engineers in France. Because they are just as responsible for delivering a 100% survivable ditching as the men in the cockpit. The reason everyone walked (floated?) away from that incident was because of excellent CRM, a very good call by Sully (He activated the APU which kept the aircraft in Normal Law) and Airbus' Alpha protections.

So what's the downside? We'll I'm not a pilot - I'm an experienced Control Engineer - servo systems, process control, you name it - the kind of safety critical systems you find in an Airbus are found everywhere from a Nuclear power station to your Toyota Prius. If you ever crash you car into a power pole and bring down the high voltage lines, there's a good chance that my own software kept you from being fried. Even electric wheelchairs can kill you - should one suddenly propel you off the curb and into traffic. For fun I work out Laplace Transforms.

The problem with all safety critical systems is that you want them to fail-safe. And, when you consider protections and they priorities, you need to start off with a bit of FMECA analysis. The trouble is that some systems cannot fail-safe - you have to compromise by "failing-as-safe-as-you-can"

Another case in point, related to a relatively simple system I developed: You're a skydiver. Your reserve canopy has a microcontroller AAD (Automatic Activation Device). It has one simple objective. If you are going to hit the ground, and haven't deployed your main canopy, or for some other reason, it has not deployed correctly - the AAD will deploy the reserve canopy for you. But while you're freefalling, the AAD self-tests and detects a fault. So what should it do while you fall at 120mph directly toward the ground? What's the *safest* thing for it to do? I'll leave it open for you. But it's not as simple as you think.

Back to Airbus. The downside of an automatic protection system is that it adds a layer of complexity to debug if it fails. Though Airbus' fallbacks are well designed - this is going to mean you have a tougher task to manage when there is a fault. This means Airbus Pilots have to be smart.

But given the huge safety benefits of their automated protections, the answer is not to remove them - the answer is to improve their robustness, refine their fallback modes and ensure that failure conditions are adequately trained and simulated.

To round off in line with my argument about protections and in a roundabout way come back on topic: I don't understand why Air France didn't purchase BUSS (Back Up Speed Scale) - designed specifically for loss of speed data incidents.
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