hello,
i understand that the different computere systems are designed to monitor each other and take on duties of each other if they fail and that has always been a comfort to me when flying.My question is this though if for whatever unimaginable millions to one situation the computers were not doing there job but fuctioning in some incorrect way can the pilot overide them ie,if the pilot inputs on the joystick to climb or descend but teh computer incorrectly disagrees does the place submit to the pilot or what might be incorrect data frothe flight management system?

Thanks Diggerman: that's actually a really good question.

Ultimately, the airbus is fly-by-wire, which means there is no mechanical override of the computers.

In fact, the only thing connected to the joystick I use to fly the airplane is a plug to a wire bundle.

However, as pilots, we can chose to turn computers off if one is behaving badly - and usually, the airbus is smart enough to know which one that is, and turn it off for us.

Also, we can turn off the "automated" functions of the computers, and put them in what I call "dumb mode" - which means the computers don't think, they just do what I tell them - up, down, left, right, etc.

There are many rumors as to just how many computers are on an airbus - maybe someone wiser than me might chime in - But I've heard somewhere in the realm of 500, all told.

Additionally, Airbus knew that the success or failure of the airplane depended on the reliability of the flight computers - and created so many redundancies of redundancies even us pilots can't even follow it all.

In the chance that ALL computers suddenly decided to go on the fritz - or they all turned off - we have a very minor control of the airplane (we call it "mechanical law"). I've simulated that situation, and managed to "live" and "land", but the instructors at the simulator facilities tell me the survival rate is about 50%. However, all I need is ONE independent flight computer, out of five independent computers, and then I have everything I need to make a landing without too much issue.

Does that answer your question?

hi,
sort of !!!
what turned it on its head for me and this i believe applies to all fly by wire aircraft boeing or airbus is that basic flight control is possible with complete computer failure but that in the case of incorrect ifo being fed to the computers there input or activity could counter the pilots control of the plane. i believe the new a380 has a flight computer control opt out for the pilot, why just for that model and what is the difference in what this provides for the pilot?

An interesting question. Another one for me to ask the experts in our training department. Let me see what they come up with and I'll get back to you on that.

There is, I believe, an error-checking routine that, if one computer starts demanding something odd, the other computers either override or disconnect that computer. But that's off the top of my head, so don't quote me on that. Thanks for the great question - I'll try and get the smarter guys thinking on that one, too.

I realize the odds of your question - with 5 separate independent flight control computers - are pretty slim, but it's an interesting thing to think about nonetheless.

-Chas


<-- The airbus?

Update,

I still haven't heard back yet from the brain trust, but I haven't forgotten the question. Stay tuned.

i take it the questions a tricky one!
ok another question,why dont airlines insist on one of each manufaturer pitot tubes?
After all my understanding is that teh main flight comuters arent the same type?

Andy

Andy,

Sorry for the long delay in response. From what I've been able to gather, Airbus is considered a "New Generation" Aircraft, and numerous "exemptions" have been granted to the aircraft because "that just can't happen."

Numerous "That just can't happen" incidents have occurred on the airplane, without fatal results, and several "AD's" (Airworthiness Directives) have been issued since the airplane was first certified. For example, the "Standby" attitude and airspeed indicator was not "independently powered" originally because Airbus claimed that it was "impossible" for such a necessity. Thirty-two complete power failures later, the FAA has issued an AD to ensure that Airbus aircraft MUST comply with this FAR.

All rules, and aircraft manufacturing processes, are governed by the "blood rule" - until a lot of blood is spilled, no rules are written.

For example, the Pitot Tubes, until the Air France incident, were an "Advisory" change, and not required. Now that people have died, it has become mandatory.

It is a simple "cost vs. liability" question. If it is cheaper to kill you than fix the problem, then sorry... you're dead.

That's aviation.