TheBigOne
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Airbus A320 Electrical Failure Question.

Mon Nov 28, 2005 10:17 pm

The recent failure of electrical supply to the primary and standby flight displays on a BA A320 has got me thinking. I suppose that the primary flight display and standby instruments are powered independently from each other. Despite this both systems suffered electrical failure. What are the chances that such a failure could occur with the FBW controls and therefore render the controls useless? While very unlikely I would like to know if Airbus issues guidelines in the event of total electrical failure.

As my interest in aviation is purely a hobby, please forgive me if I have asked a stupid question!
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HiFi
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RE: Airbus A320 Electrical Failure Question.

Tue Nov 29, 2005 12:02 am

Quoting TheBigOne (Thread starter):
What are the chances that such a failure could occur with the FBW controls and therefore render the controls useless?

Since this kind of event is catastrophic, I'd say that chances are under 10e-9 (or else it wouldn't have been certified). To find a more detailed answer should not be very simple, as manufacturers tend to be very cautious with this kind of design information.

Quoting TheBigOne (Thread starter):
While very unlikely I would like to know if Airbus issues guidelines in the event of total electrical failure.

A black airplane situation (a/c relying only on battery power) is very hard to see, usually because besides all the redundancies of the electrical system, the a/c has some ultimate resource (a RAT, for example).
And yes, there's probably a procedure to be followed in case of total electrical failure..
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TheBigOne
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RE: Airbus A320 Electrical Failure Question.

Tue Nov 29, 2005 2:59 am

Thanks HiFi

Quoting HiFi (Reply 1):
A black airplane situation (a/c relying only on battery power) is very hard to see, usually because besides all the redundancies of the electrical system, the a/c has some ultimate resource (a RAT, for example).
And yes, there's probably a procedure to be followed in case of total electrical failure..

So any idea what kind of procedures would be followed in this situation?
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Jeff G
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RE: Airbus A320 Electrical Failure Question.

Tue Nov 29, 2005 9:59 am

It is difficult to imagine all electrical power being removed from the airplane in flight. There are a number of systems that would have to fail simultaneously, including two batteries, for that to happen. Ultimately, you'd have to fly the airplane using rudder, pitch trim, and thrust long enough to get some power back on the airplane, either through a restored generator or the RAT. It is theoretically possible to land the plane using no flight computers at all, but it's not something that you'd practice. The chances of such a scenario occurring are so remote that it's just not a major part of anyone's training syllabus. That said, I did it once in the simulator. It was challenging, but definately doable and kinda fun. Then again, I'm the kind of guy who thinks dead sticking planes in in the sim is fun.
 
HiFi
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RE: Airbus A320 Electrical Failure Question.

Wed Nov 30, 2005 1:06 am

Quoting TheBigOne (Reply 2):
So any idea what kind of procedures would be followed in this situation?

It probably contains something of the sort:
- land as soon as possible.
- try to get one of the generators back alive.
- check battery power.
- deploy RAT, even if there usually is an auto deploy feature.
- depending on the type's electrical system architecture, shed non essential loads.
- fly at a recommended altitude/speed (depends on the type) and avoid bad weather/icing conditions.
- a list of unavailable equipment/functionalities.
- land with a recommended a/c configuration and speed.
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DH106
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RE: Airbus A320 Electrical Failure Question.

Wed Nov 30, 2005 1:21 am

There's all these alternative power sources, but what would happen if some sort of fairly massive short happened. Presumably circuit breakers would pop and fuses blow, but then it wouldn't be a matter of backup power supplies... the aircraft would be incapable of receiving power from it's various supplies because the short would render the power useless....
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HiFi
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RE: Airbus A320 Electrical Failure Question.

Wed Nov 30, 2005 1:40 am

Quoting DH106 (Reply 5):
There's all these alternative power sources, but what would happen if some sort of fairly massive short happened. Presumably circuit breakers would pop and fuses blow, but then it wouldn't be a matter of backup power supplies... the aircraft would be incapable of receiving power from it's various supplies because the short would render the power useless....

A modern electrical system has several AC busses, several DC busses and some emergency or backup busses. All of them segregated from the other so that it is unlikely that a failure on one of them will affect the others.

Of course, some are dependent... for a very simple example, bus2 may only be available if bus1 is powered, but a failure on bus2 does not affect bus1 and vice-versa.

That established, essential equipment have more than one power source. An inertial unit, for instance, may have 2 power supplies, one on bus1 and one on bus5. If the CBs on bus1 pop-out, the inertial unit will be powered through bus 5 (an alternative route, not necessarily an alternative generator/power source).

Hope this helps.. Big grin
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Pihero
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RE: Airbus A320 Electrical Failure Question.

Wed Nov 30, 2005 9:34 am

TheBigOne,

You may research in one of the air accident sites the case of the Air Transat A330 which was allowed to run out of fuel : no engine generator, no APU generator.It was just left with the batteries and the RAT.
The crew managed to glide it to the Lajes airport. And it still had the integrity of it's flight controls (granted without all the protections...).
That's about the most extreme failure you could imagine.
On the same subject, with engines available and/or the APU, a major el;ectrical failure will cause you to go into a failure research and isolation procedure, followed by a reset of most available components after the faulty generation system or bus has been identified and isolated.

Otherwise, it's pretty much like HiFI's description. Difficult to elaborate any further than HiFi did as power sources and system requirements are so numerous. We pilots learn and retain the most important switchings :For instance, the BA incident (initial loss of captain's instruments and the upper ECAM) is a trigger for a faulty ac essential bus. Before anything else I personally would have confirmed the fault with the electrical panel (overhead) and tried to re-power it through its alternate source (in this case the #2 ac bus)...but as the saying goes, hindsight is always 20/20.

Regards.
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fr8mech
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RE: Airbus A320 Electrical Failure Question.

Wed Nov 30, 2005 1:56 pm

The answer you are looking for is that there would be no control inputs to the flight controls since they are dependent on electrical power.

The reason this condition is allowed to exist is because a COMPLETE electrical system failure (no gens, no batteries, no standby, no RAT, nothing) in a modern airliner due to a massive short disabling the busses is just short of impossible. The only reason I don't say completely impossible is because statistics teaches us that there is always some probability of an event.

But just because some probability exists doesn't mean you have to plan for it. If it ever happens, it will be studied and corrections put in place or declared a statistical aberration and we'll all move on.
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