A330/A340 EAD (AoA PROBES)
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Tyro said
There is no artificial spring feel in the Airbus, that I know of. Of course there is feel: that of the spring, and totally unrelated to any aerodynamic variable. In normal law, there is a relationship between load factor and the angle and spring force. That's why it is very natural to fly in normal law. But in direct law, there is absolutely no relation with anything, be it speed, load factor, or whatever. Depending on the circumstances, the same spring force will have very different effects.
Artificial feeling in hydraulically operated airplanes is dependent on speed, one way or another, linearly or square of speed. It does not resemble the feeling of a directly mechanically linked FCS exactly, but enough for a pilot to instinctively feel if they are making too hard an input, and how the airplane should respond to a given input. You don't have that on a sidestick when in direct law.
The B777 went to greater lengths of complexity to achieve a pilot instinctive FCS, being it fully computerized. It is difficult to get the advantages of fbw and still make it feel like a conventional airplane that is very easy to fly. When the B777 reverts to direct law I believe it still retains artificial feeling and then it feels like a conventional airplane, only not so easy to fly, where you can trim stick forces.
The side-stick has artificial spring feel which returns the SS to neutral.
The spring force increases with increasing displacement.
- how is that different to a conventional yoke fitted with artificial feel and hydraulically operated control surfaces? I am not a test pilot but it sounds very similar to me...
The spring force increases with increasing displacement.
- how is that different to a conventional yoke fitted with artificial feel and hydraulically operated control surfaces? I am not a test pilot but it sounds very similar to me...
Artificial feeling in hydraulically operated airplanes is dependent on speed, one way or another, linearly or square of speed. It does not resemble the feeling of a directly mechanically linked FCS exactly, but enough for a pilot to instinctively feel if they are making too hard an input, and how the airplane should respond to a given input. You don't have that on a sidestick when in direct law.
The B777 went to greater lengths of complexity to achieve a pilot instinctive FCS, being it fully computerized. It is difficult to get the advantages of fbw and still make it feel like a conventional airplane that is very easy to fly. When the B777 reverts to direct law I believe it still retains artificial feeling and then it feels like a conventional airplane, only not so easy to fly, where you can trim stick forces.
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Originally Posted by DOZY
With Airbus FBW, the protections do not "take over", they limit and constrain attitude.
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@CONF - I'm not in denial - the alpha protections follow pilot input up until the point safety boundaries are reached and will maintain that, in much the same manner as the T7 will progressively counter input through the force-feedback. Of course, as the Mach number increases, the pitch down will also increase, but it's not going to suddenly force the aircraft into a significant dive, in fact it won't descend at all if corrective action is taken.
This recent modification seems to have been an attempt to counter the risk of icing of the AoA vanes, and it would appear that a set of circumstances outside of the certification testing have shown the fix to be inappropriate.
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Originally Posted by DOZY
@CONF - I'm not in denial - the alpha protections follow pilot input up until the point safety boundaries are reached and will maintain that, in much the same manner as the T7 will progressively counter input through the force-feedback. Of course, as the Mach number increases, the pitch down will also increase, but it's not going to suddenly force the aircraft into a significant dive, in fact it won't descend at all if corrective action is taken.
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It's reasonable to presume this is the first incident of this type, as the AoA probes referenced are a new fit item. As such no procedure existed prior (nor was there any need for it).
Airbus know how work their automation .. and so they were (are) aware of the consequence on the flight automation if this AOA probes problem happens ...
Is that they thought such an event, however, was unlikely to occur?
No procedure needed ?
Even a prayer for good luck?
Last edited by jcjeant; 20th Dec 2012 at 15:03.
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jcj - I think you're reading a different meaning into my words than I intended. This problem is a new one that seems to have arisen with a recent modification to the AoA vanes, intending to solve the issue of the icing up of one vane that occurred on AF447. It appears that the fix passed certification and began to be implemented, but the certification tests were not sufficient to catch this new issue (in other words the fix seems to have made the problem worse - with all three vanes freezing in certain conditions).
As with the Thales AA pitot tube design, this incident shows that the certification process needs to be revised based on the evidence presented. EASA and Airbus seem to have been pretty quick in getting the EAD and workaround published once the problem was known.
As with the Thales AA pitot tube design, this incident shows that the certification process needs to be revised based on the evidence presented. EASA and Airbus seem to have been pretty quick in getting the EAD and workaround published once the problem was known.
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jcj - I think you're reading a different meaning into my words than I intended. This problem is a new one that seems to have arisen with a recent modification to the AoA vanes
Older AOA vanes or new AOA vanes can have the problem of this particular incident
It's not unpredictable ... even if certifications are bad or good
All in a aircraft is certified and all can fail one day or another
You can't of course have a procedure for every items who fail in a aircraft .. but it must be procedures when important item fail
AOA vanes are important items necessary for the safe conduct of the flight
The implication of the failure described in this post on the flight automation was predictable by the constructor (like a fail of Pitot for what it was procedure already available .. as it's predictable)
But unfortunately no procedure was available for the pilots at the time of this incident .. and it was a risk that this incident turn in a accident ...
Fortunately .. the pilots not goofed .. Airbus yes IMHO
Last edited by jcjeant; 20th Dec 2012 at 16:45.
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jcj - the EAD applies specifically to the modified AoA vanes only. The modified AoA vanes are the only type to have suffered a triple failure. Airbus didn't have procedures for triple failure prior to this EAD and nor did any other manufacturer, so why pick on them?
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Being an EAD bulletin, it's likely that the incident report is still in progress. I did have a hunt online, but nothing as yet. There are a couple of stories on Flight, but some are subscriber-only.
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Originally Posted by DOZY
The modified AoA vanes are the only type to have suffered a triple failure. Airbus didn't have procedures for triple failure prior to this EAD and nor did any other manufacturer, so why pick on them?
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Dozy
In case of an AoA failed in such a way that erroneously gives a stall output, the normal law would pitch down to reduece the AoA. Because it would remain fixed, erroneously, FCS would keep pitching down... Or so I believe.
The fbw can take over and we need to be able, firstly, to detect that normal law is no longer desirable and secondly to revert to a safe control law.
In case of an AoA failed in such a way that erroneously gives a stall output, the normal law would pitch down to reduece the AoA. Because it would remain fixed, erroneously, FCS would keep pitching down... Or so I believe.
The fbw can take over and we need to be able, firstly, to detect that normal law is no longer desirable and secondly to revert to a safe control law.
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"undue" stall warning
but never in 40 years have I ever heard of an 'undue' stall warning....
BEagle, an "undue"stall warning is indeed a real occurence. I flew a lot of L-19 (Birddog) tows (5000 plus) and the stall warning buzzer would regularily go off in turbulence, such as, for example, 15 kn wind and strong thermal conditions. Maintaining attitude always got us (glider and self) through this.
Similarily, when towing through a rotor in mountain wave conditions would cause the same.
BEagle, an "undue"stall warning is indeed a real occurence. I flew a lot of L-19 (Birddog) tows (5000 plus) and the stall warning buzzer would regularily go off in turbulence, such as, for example, 15 kn wind and strong thermal conditions. Maintaining attitude always got us (glider and self) through this.
Similarily, when towing through a rotor in mountain wave conditions would cause the same.
Thread Starter
I would term that a 'spurious' stall warning. I had a spurious stall warning at about 400 ft on a flapless approach in a VC10 when sticking AoA probes (the jet had been in the desert without a decent wash for too long) jumped, triggering phase advance and a sudden stick push.....
Direct reading AoA gauges should be installed in all airliners. Not some extra thing displayed electronically, just a simple, direct instrument.
The Russians used to have a combined AoA gauge and g-meter in many of their aircraft. What an excellent safety aid that must have been!
Direct reading AoA gauges should be installed in all airliners. Not some extra thing displayed electronically, just a simple, direct instrument.
The Russians used to have a combined AoA gauge and g-meter in many of their aircraft. What an excellent safety aid that must have been!
Last edited by BEagle; 21st Dec 2012 at 14:36.
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In the press .....
Des pilotes Air France exigent le retrait de sondes d'Airbus - Le Nouvel Observateur
Google*Traduction
Des pilotes Air France exigent le retrait de sondes d'Airbus - Le Nouvel Observateur
Google*Traduction
Air France pilots require the removal of probes Airbus
"We can not meet the manufacturer and the authority just by a simple procedure permanently supplement what appears to be a serious deficiency of an element as vital to the conduct of the flight," said Jean-Louis and Barber, president of the AF SNPL Alpa.
"We can not meet the manufacturer and the authority just by a simple procedure permanently supplement what appears to be a serious deficiency of an element as vital to the conduct of the flight," said Jean-Louis and Barber, president of the AF SNPL Alpa.
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The fbw can take over and we need to be able, firstly, to detect that normal law is no longer desirable and secondly to revert to a safe control law.
I'm all for waiting to see the incident report before making sweeping judgements. I find the fact that Alpha Floor is not mentioned interesting, as I would have expected it to have been activated if there was a manual pitch-up command given in that circumstance. Equally intriguing is the fact that the crew managed to correctly troubleshoot the situation and return the aircraft safely to the ground despite having no forewarning of the problem. Someone out to bash Airbus at any opportunity probably won't care about such questions, but if we're being open-minded about things it should definitely give pause for thought.
@jcj - No-one's talking about the Airbus ADR procedure being a permanent solution - it is clearly presented by the EAD bulletin as a temporary workaround while the AD is being implemented on the affected airframes.
Last edited by DozyWannabe; 21st Dec 2012 at 16:29.
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Four years ago, AF pilots threatened strike if AF did not immediately obey the AD requiring pitot probe replacement.
After 228 people were killed in AF447....
Once bitten. Twice shy...
After 228 people were killed in AF447....
Once bitten. Twice shy...
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There were a lot more airframes in the AF fleet alone with the Thales AA probes than there are airframes in the worldwide fleet with these AoA vane modifications. I suspect the AD will be implemented with all due haste.