Well it is possible, in direct law. If you're asking if it's possible for control inputs not to be fed through a computer, then no, it's not possible, just as it's not with the 777 or 787. But they still can fly like conventional aircraft. The side sticks do not have cables in them linked directly to the control surfaces, just as practically any large jet doesn't now a days, the 737 was in fact the last ever large jet to have built in mechanical back up. If you lose all electrics in a 777, 767, 757, 787 then you're done for, that's why they have a RAT, so that the computers and hydraulic servos can be fed and operated in event of a loss of all electricity.

 

Regards,

Ró.

Well it is possible, in direct law. If you're asking if it's possible for control inputs not to be fed through a computer, then no, it's not possible, just as it's not with the 777 or 787. But they still can fly like conventional aircraft.

 

Regards,

Ró.

 

Thanks.

Another theorethical question then:

How would you switch to Direct law, in normal conditions, without lowering

the gear ?

 

Guy

I imagine freshly type rated Airbus and 'therefore' ex Boeing pilots to do all their flights without retracting the gear now. ^_^ Now we know why Ryanair only flies Boeing.

 

'So you are new on the Bus, huh?'

Yeah, how do you know?

'Three green'. :lol:

 

Adding a bit on the Concorde FBW ways and the 'laws' in place. There is something, scroll down that page. http://heritageconcorde.com/technical-2/flying-controls-systems/concorde-fly-by-wire-system

Fairly certain you can't,not without deliberatly switching off elacs, sec's and fac's

But Ró might be able to suggest other ways. I only fix them

Well a triple IR failure would put you into direct law, so I'd imagine turning off the 3 ADIRS' would work for getting you into Direct law without dropping the gear.

 

Regards,

Ró.

But then you lose the PFD and things, right? Attitude information via standby instruments.

But then you lose the PFD and things, right? Attitude information via standby instruments.

Correct, you would be navigating by the ISIS and standby compass with ILS, LOC and ADF only, as well as good old visual flying. About as conventional as you can get, right up there with a Cessna 152...

 

Nice system detail. The RAT on the A320 only powers the hydraulics. But there's an emergency generator in the BLUE loop if I got that right.

Correct.

 

Regards,

Ró.

About as conventional as you can get, right up there with a Cessna 152...

But still faster.

 

Actually, it's quite overwhelming how much could go wrong on an airliner. By this and since the severe system breakdowns are rare, I'll leave a praise. Not only for the pilots but also for the engineers and staff around that amazing concept of an airplane. Means all manufacturers and control setups.

Alan Dix is the man!

Correct, you would be navigating by the ISIS and standby compass with ILS, LOC and ADF only, as well as good old visual flying. About as conventional as you can get, right up there with a Cessna 152...

 

 

Correct.

 

Regards,

Ró.

 

Thanks again for all the Information and also your patience ! :rolleyes:

 

We started the discussion from a statement you had made above :

 

"the pilot has the ability to override anything he wants to"

 

That seems not so easy after all !

 

Guy

"The pilot has the ability to override anything he wants to"

That seems not so easy after all !

Never said it was easy LOL... ^_^ Fact is most of the time, 99.999999999999999999999% that he'll have no need to over ride it, it will do exactly as he says or else do the correct thing, but where there's a will there's a way. Making it easy to override the computer even when it's doing the correct thing would defeat the purpose of the flight envelope protections.

 

Regards,

Ró.

Never said it was easy LOL... ^_^ Fact is most of the time, 99.999999999999999999999% that he'll have no need to over ride it, it will do exactly as he says or else do the correct thing, but where there's a will there's a way. Making it easy to override the computer even when it's doing the correct thing would defeat the purpose of the flight envelope protections.

 

Regards,

Ró.

 

I know very well that in practice there will almost never be the need to override

the computer.

 

I asked all those "silly" questions because I have very often seen this point

debated on forums like this one , without really an answer.

 

So I profited from the fact that we have such a gentle and patient Airbus Tri/Tre

here to clarify things a bit.

 

Many thanks again ! :rolleyes:

 

Btw, the Airbus Control Laws are here:

http://www.airbusdriver.net/airbus_fltlaws.htm

 

 

Guy

I often take the example from the automotive sector. Just because it's know to a broader audience. Writing in sim forums.

 

<snip for the sake of space>

 

 

I would like to expound upon your automotive analogy with an example from a slightly different perspective, from that of a new vehicle owner coming from a much older vehicle lacking all the modern safe guards. I recently purchased a 2013 Nissan Altima with the 3.5L V6. Previously I owned a 2000 Nisan Maxima with a 3.0L V6. The difference in power is very noticeable, and the newer vehicle has a much stiffer chassis and suspension so the ride quality in the new car is a huge upgrade. However, due to all the modern safe guards I am unable to drive the car as I would like to in any given situation.

 

Let me elaborate a bit. The old car had a 5 speed manual transmission and no electronic safe guards (other than the bare bones ABS that every car made in the last 20 years or so has). The new car has a Continuously Variable Transmission ("CVT" - infinite gearing possibilities) and numerous traction control technologies, most of which involve the use of the brakes. The first technology IMHO is similar to Airbus' FBW technology because it takes the operator's input and translates it into a "best" output (in the opinion of the computer). The second is like Airbus' flight envelope technology because it takes the user's input and disallows certain actions. This results in a couple of issues for me, issues that I know I can provide a better outcome than the computer's decision forces upon me.

 

The issues are these: in the first case, let's say I want to accelerate suddenly to pass or avoid a hazard. If I provide full throttle, the transmission computer takes a full second (or more, depending on the mode) to choose the "best" gear ratio. That second+ can be the difference between an accident avoided or one caused. The second case with the brakes cutting in if I accelerate "too much" and produce any wheel spin, the throttle cuts and the brakes are applied, absolutely killing acceleration. Once again this produces a scenario whereby the behavior which is averted by the computer's decision is not as bad as it may seem, i.e. the correction is more drastic than it needs to be. There is NO way for the user to override this behavior, unfortunately. With the old car, neither of these issues occurred. I could give it as much throttle input as I liked and the only thing stopping me was the inherent traction of the tires. So for me this is a case of over-engineering, and in my mind good evidence that a living, breathing person with the ability to make a snap decision is always preferred.

 

That being said, I do believe there is room for these types of protections, as they can prevent an accident or equipment damage due to "incorrect" user input. I believe the best solution is to allow the user to override the computer in case of emergency. I also believe this should apply to aircraft.

Interesting example. Unfortunately, I don't know that car in detail and therefore its setup. Return it! :lol: Seriously, that delay on the reactions sounds bad. And I agree that there may be missing a kick-down switch (being featured on the cars I know) to just take care of the escape mode if you like.

 

Sounds like the gearbox is in the eco mode and does not have a channel to sense the user's wish to get out of there ASAP. I don't know if we could call it a protective measure though.

 

On a side note and not wanting to embarrass you, you wouldn't be the first person I've met to discover a kick-down switch after actually using the car for months or even years. So maybe there is one, at the end of the throttle travel. :mellow: The systems I know already realize the acceleration of the pedal to sense what you want.

 

The handling of the brakes to 'simulate' a self-locking differential gear is pretty common. Various reasons, one of them being the cost and saved weight as your Maxima may not be aiming at the regular use of off-road paths but just rare situations where the one wheel has to be blocked (brake sets in) to allow the other one to grab Mother Earth. Downside of a normal differential gear, the brake works around it.

 

Still, if you had a self-locking differential gear installed, being the more costly and, for off-road use, better solution, you couldn't influence the self-lock too. There could be a switch to force a look even if there was no need for it, but the setting in of the self-lock when one wheel is on an ice pad and the other one has grip, can't be influenced by that. It would automatically self-lock and lead to torque on the 'grip' wheel.

 

The early brake methods came in rough, I agree. If they still do, it's sad to hear. Well, they don't get used that often unless you operate a lot on ice and snow. From my knowledge, the brake use fades out above a certain speed. A low one, around some 12 or so mph. The system later just limits the engine power in general to allow more traction to develop due to less excessive force being applied. Well, depends on the model. Details.

 

 

The ability to override protections surely is an often discussed item. As we saw. While I think that some folks relate the actual override inability to 'losing control' or even 'not being in control', the word of the pilots flying such planes is that it's behaving just like any other plane. It helps keeping in mind that the protected item is the flight envelope, the limit which is defined by physics acting on the plane.

 

So, regardless of the protections in place, no plane is able to fly outside of that envelope. The laws of physics don't care for the hour count of the Captain and they also don't care if he has aced every test in the last 20 years. They would care for his weak 5 seconds where he decides to stall the plane for whatever, somehow even 'comprehensible', reasons.

 

So there's nothing stopping you from setting MCT or even TOGA thrust for example. No forced eco mode. This means, while you may be complaining about the erm stubborn engineering on that car, the downsides on reaction times or the wrong gear so far haven't been a problem with the planes. My car analogy was limited, it just shows. :blush:

 

 

Now what's the point on hard limits then? It makes sense to look at the soft ones first. The ones which can be overridden by more force on the yoke/stick or by just disregarding other clues. Do those override events happen? Yes. What's the outcome of those, did the override correct any errors in the system and therefore saved the plane? From the reports, no. :(

 

To give an example, the stick shaker or, on some planes, stick pusher can be disregarded and overridden. By this, the crew in panic may not be the one realizing that even that last safeguard is there to help or to remind them about leaving their flight envelope. You don't get just one warning when approaching a stall, you pass by a set of those. Since you've disregarded e.g. the low energy warnings before, it's not unlikely that even a shaking control column or the pushing from the system gets disregarded/overridden too. Take the Colgan Air 3407 for example.

 

So if there's a confused (thinks overspeed, but actually is flying close to stall) or paniced crew (acts in fear, not in logic) around, there's no way to get trough to them with soft limits. They will, in the believe of doing the right thing, override them. That's the thinking behind hard limits.

 

Now I wouldn't promote them being the ultimate problem solver. PR folks may do this. Same as I wouldn't promote that Airbus crews are any different when it comes to airmanship in regard to other crews. Which would be the negative assumption sometimes being spread.

 

If pilots and companies, maybe even aviation authorities, take such systems as a reason to let go on crew training, it would be wrong. With money driving a business in the first place (and not safety), this mind set, for me, offers a far greater threat to look at.

 

 

So while people seem to think that, in a tight situation, there's an ace on the yoke, clearly knowing that he just has to fly the plane upside down now, then stall it, recover and later land at the destination as if nothing happened, the actual rw reports (and not the ones from Hollywood, think Denzel Washington) and CVR recordings will tell that there are crews being totally out of the loop and therefore confused.

 

If they are not, they don't, by themselves, approach the flight envelope limits. So the limits and protections are there, but you won't experience them. If you get confused and if the system has all the data it needs (Airbus, normal law active), it will keep you away from reaching them.

 

Mentioned before. One shouldn't underestimate the lack of logic on the behaviour of humans when it comes to stressful situations. I agree with you that, in more calmer situations and with a pilot setting up and planning a difficult manoeuvre, there is room for letting him fly into the warnings and close to the limit.

 

A prepared pilot is a good decision maker, a surprised one not always is. Well, how commonly do the airline folks plan for a stall or 2.5G+ load situation?

 

Side note. As far as I can tell, even the military FBW planes limit G loads to avoid that a panic push/pull on the stick leads to structural damage, loss of control or 'just' an unconscious pilot.

Never said it was easy LOL... ^_^ Fact is most of the time, 99.999999999999999999999% that he'll have no need to over ride it, it will do exactly as he says or else do the correct thing, but where there's a will there's a way. Making it easy to override the computer even when it's doing the correct thing would defeat the purpose of the flight envelope protections.

 

Regards,

Ró.

 

 

To SUMMARIZE and conclude our discussion from yesterday, I think I must modify

my statement from above a bit. This must be about right :

 

It is NOT possible to fly the Airbus in NORMAL conditions like a conventional aircraft

(that means in DIRECT law).

 

That means:

To get the Airbus in DIRECT law you MUST set some ABnormal conditions:

-either switch off some computers (FAC1/2) and lower the gear

-or switch off all ADIRS (and loose the PFD/ND)

 

I read somewhere else that If you switch off ALL FAC/ELAC/SEC computers you

pass in MECHANICAL backup mode, where it is very difficult to land, as you said

above. ("crash in a semi controlled fashion...")

 

And then it's also no FUN to fly in DIRECT mode as you said above

"she handles like a 3 legged bull in direct law". :rolleyes:

 

And once more: those are just THEORETHICAL considerations to better understand

the Airbus systems. I know very well that in practice there will NEVER be the need

to pass voluntarily in DIRECT law.

 

PS : Another good summarization of Airbus systems is here:

http://www.dutchops....html#flightlaws

 

Guy