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PHD. MBA. MHS. Type rated on A350, A330, B777, B747-400, B747-200, B757, B767, B737, B727. International Airline Pilot / Author / Speaker. Dedicated to giving the gift of wings to anyone following their dreams. Supporting Aviation Safety through training, writing, and inspiration. Fighting for Aviation Safety and Airline Employee Advocacy. Safety Culture and SMS change agent.

Tuesday, September 14, 2010

A320 verses A330 ... Fault Redundancy

Opinions are just that... and everyone has one.

An 'industry official' (don't you love them?) stated in the ' article that 'the flight control system on A320s has greater fault redundancy than does the widebody’s'. Is this a correct assumption, do you think?

The A320 has three types of computers:

ELAC: elevator - aileron computer.
SEC : spoiler elevator computer

FAC : flight augmentation computer - which does a lot of the functions that the Envelope function of the FMGEC does.
Note… The A320 does not have a fly-by-wire rudder.

However the A330's primary and secondary computers spread the control of the various surfaces over all of the flight control computers. For redundancy, ailerons, elevators, rudder, and the THS can each be controlled by more than one flight control computer.

On the A330 should the primary computer, hydraulic system, or servo fail… backup flight control computers and hydraulic servos automatically take over. Failure of any one hydraulic system or flight control computer will not result in control loss to any ailerons, elevators, the rudder, or THS.

Each hydraulic system powers at least one aileron on each wing, one elevator, two spoilers, and the rudder, ensuring control following any dual hydraulic failure.

To claim that the A320 is MORE redundant is an "amazing" claim. The 330 is set up that each flight control computer can control ailerons, elevators, and some spoilers. All except for 1 can control the rudder. Not to forget there's a separate backup rudder control scheme, with its own generator and control computer.

The 320 can't make that claim. Additionally, on the 320, it's much easier to end up in Direct Law, and if you are in alternate law you are going to be without the autopilot…. I think in all cases, but not completely sure.

On the 330 the autopilot is often available in alternate law, and you don't automatically degrade to direct law from alternate law. The 320 almost always reverts to direct law from alternate law when the gear is lowered.

Now… if that article meant the fault redundancy that relates to the internal processing algorithms, comparing data sources, instead of the macro flight control architecture configuration that was discussed above… Never mind. I'm not sure. A person with a PhD on the internal processes will need to make that assertion.

However, one significant point that was in error on that article: “Currently, the probes are certified only to handle temperatures of up to -40C…” On the A330 the ISA at and above FL350 is “-55C."

This statement somewhat makes you doubt the entire article.

Now, don’t be too impressed by my advanced wisdom on the A320. I’m on a long trip, at the end of 30 days on the road, working on my novel, and flying. I don’t make this stuff up... I have “People.” Thank you Bill!


Simon, I will answer your next questions tomorrow.

Happy Flying and Enjoy the Journey!



  1. Thank-you for that excellent answer Karlene! You have definitely explained it perfectly. Of course we ARE impressed by your wisdom, even if you have 'people', but also by your writing.. It takes real skill to put all that information down and make it so enjoyable to read.
    Now here's a slightly surreal sight: Two people sitting in the wilderness area of western Tasmania, hundreds of kilometres from the nearest airport, discussing the merits of the A330 and finally having insight on that 'misleading' article.
    Have a wonderful flight home and thank-you again!


  2. Simon, Thank you so much. You should be a writer! I think my next novel will have to visit the shores of Tasmania! I have a visual...and I like it!
    More to come tomorrow!
    Have a wonderful day!


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