Another thought - crazy as it seems but could the PF have thought he still had stall protections?

 

Alright sorry for the delay in posting, places to go, oceans to cross ect...

 

To my point,

For the final time, regardless of protections available, you never pull back in a stall, you ALWAYS push forward. Heck if I got into a stall and saw my FO pulling back on the stick I'd clatter him with the blasted FCOM!!! It's just not done, ever, never, at all, never, period!

 

If I told you there's typically a net at the bottom of that cliff, you don't just jump off it do you? The same thing applies here....

 

Capt. Rónán O Cadhain.

For the final time, regardless of protections available, you never pull back in a stall, you ALWAYS push forward.

Capt. Rónán O Cadhain.

 

I don't dispute this in any way shape or form Ró, and nor do I dispute the fact that the PF did totally the wrong thing! But (and this is a very big but) to push forward in a stall you first have to identify that you are in that stall. I believe the PF never did that, he was too busy trying to keep the wings level and was overly concerned with an overspeed that didn't exist, even with the stall warning sounding. By the time the aircraft was actually stalling he was in total confusion as to what was happening.

I don't dispute this in any way shape or form Ró, and nor do I dispute the fact that the PF did totally the wrong thing! But (and this is a very big but) to push forward in a stall you first have to identify that you are in that stall. I believe the PF never did that, he was too busy trying to keep the wings level and was overly concerned with an overspeed that didn't exist, even with the stall warning sounding. By the time the aircraft was actually stalling he was in total confusion as to what was happening.

That I'll accept, but that's not what I'm disagreeing with, I'm disagreeing with the mentality that was displayed in the quote that if you have protections you can do as you wish...

 

Rónán.

That I'll accept, but that's not what I'm disagreeing with, I'm disagreeing with the mentality that was displayed in the quote that if you have protections you can do as you wish...

 

Rónán.

 

Well yes, the mentality in cockpit that night was totally wrong - even if the PNF had a suspicion that they could be stalling, he did nothing and when the captain arrived he seemingly neither identified the stall nor took action to resolve it.

 

Re the protections (this is a separate discussion really) I thought that with full protections in place (is that what is referred to as Normal Law?) one could pull back on the SS and hold it there and the aircraft would never stall because it would stop pitching the aircraft up as it approached stall and selected MCT as needed? Happy to be educated here, it's something I know little about.

Re the protections (this is a separate discussion really) I thought that with full protections in place (is that what is referred to as Normal Law?) one could pull back on the SS and hold it there and the aircraft would never stall because it would stop pitching the aircraft up as it approached stall and selected MCT as needed? Happy to be educated here, it's something I know little about.

 

The only way to break out of a stall is to reduce your angle of attack. Fly by wire can keep a plane from departing, it won't keep you from a stall. (In fact, fly by wire is what is used by aircraft designers to keep planes 'controllable' during stalled flight) A departure is when the aircraft leaves controlled flight, when it rolls off and pitches down, and tumbles out of the sky on its own. You may think that is a bad thing, But it is actually nature's way of taking a pilot who does not know what he is doing out of the picture so that the aircraft can break a stall on its own and save itself. If the computers hadn't kept working the rudder and spoilers automatically to keep the plane from departing, that airbus would have tumbled, and given enough altitude, may have allowed all aboard to live by breaking out of that stall naturally.

 

In science, there is a law called Occam's Razor. It basically states that the simplest solution is probably what's right. What is simpler? For a pilot to think that he is in a mysterious overspeed for 5 minutes when all available indications were that he was too slow? Or for a pilot to see that he is descending and pull back on the stick to climb?

If the computers hadn't kept working the rudder and spoilers automatically to keep the plane from departing, that airbus would have tumbled, and given enough altitude, may have allowed all aboard to live by breaking out of that stall naturally.

 

Roll spoilers we're not automatic, and automatic rudder input is only for yaw damping. What kept the aircraft from completely departing was the full nose up autotrim in Alt2 combined with TOGA thrust. The aircraft basically sat balanced and stable on it's tail the whole way down.

I don't think we're talking about the same thing here. FBW, by my understanding, just means that the control surface is not operated directly by the control column - as used by countless aircraft types Boeing and Airbus alike. What I am talking about is the specifics of Airbus's additional protections that were incorporated into their FBW flight control systems - wasn't that one of the much vaunted features at the A320's launch, the fact that it was impossible to stall in Normal Law with the protections in place (and unsuccessfully demonstrated at Habsheim, but that's a different story)?

 

Edit: That's to KevinAu, rather than FLEX

Roll spoilers we're not automatic, and automatic rudder input is only for yaw damping. What kept the aircraft from completely departing was the full nose up autotrim in Alt2 combined with TOGA thrust. The aircraft basically sat balanced and stable on it's tail the whole way down.

 

Ironic that if the plane wasn't so well designed to be balanced and stable, it would have had a better chance of surviving.

The fact that the aircraft behaved so docile has surprised a lot of people including Airbus.

 

Turbo - I don't think it really matters, they we're in Alteranate law and would have definitely known what that meant. A msg on the ECAM would clearly say ALT LAW PROT LOST (alternate law protections lost)

I don't think we're talking about the same thing here. FBW, by my understanding, just means that the control surface is not operated directly by the control column - as used by countless aircraft types Boeing and Airbus alike. What I am talking about is the specifics of Airbus's additional protections that were incorporated into their FBW flight control systems - wasn't that one of the much vaunted features at the A320's launch, the fact that it was impossible to stall in Normal Law with the protections in place (and unsuccessfully demonstrated at Habsheim, but that's a different story)?

 

You're confusing stalling with departing. High angle of attack and high pitch attitude 'protections' like what the Airbus had will not stop an airplane from mushing into the ocean like they did. The only thing that those sort of 'protections' protect from happening is a violent, tumbling, out of control, departure of flight. That does not mean the aircraft can't sit there, all trimmed out and stable, at maximum angle of attack, maximum drag, and maximum descent into the ocean.

 

The misnomer that a lot of pilots have, is that the stick is used to control altitude. If you want to climb, you pull back, and if you want to descend, you push forward. The only thing that the stick controls is angle of attack. And in most aircraft, the only and most proximate indication of aoa is airspeed. Low airspeed indicates a high angle of attack. High airspeed indicates a low angle of attack. And the only thing that determines whether a plane is stalled or not is angle of attack. Not MCT. Not pitch attitude. By controlling angle of attack, the stick controls airspeed. By continually pulling back on the stick, the pilot was commanding the plane to fly at slowest speed and maximum angle of attack. That's what the computers were told to do by the pilot, that's what they gave him. Rate of climb or descent is a product of what you do with angle of attack. When flying at slowest speed/maximum aoa, drag is high, requiring lots and lots and lots of thrust to counteract the drag in order to maintain altitude. Even at max thrust, an airliner does not have enough 'lots' of thrust to keep a plane airborne at max aoa. That is why they descended into the ocean, as balanced and protected as they were.

Well yes, the mentality in cockpit that night was totally wrong - even if the PNF had a suspicion that they could be stalling, he did nothing and when the captain arrived he seemingly neither identified the stall nor took action to resolve it.

 

Re the protections (this is a separate discussion really) I thought that with full protections in place (is that what is referred to as Normal Law?) one could pull back on the SS and hold it there and the aircraft would never stall because it would stop pitching the aircraft up as it approached stall and selected MCT as needed? Happy to be educated here, it's something I know little about.

 

To the best of my knowledge, yes. If Normal Law is active the alpha floor protection will not allow the plane to exceed the critical angle of attack, and will apply maximum power if necessary, which together will prevent the plane from entering a stall. Though, as has been mentioned before, this still doesn't make holding full back pressure on the SS for several minutes a smart thing to do. Even with all the protections working I don't think there is a situation to which this would be the appropriate response.

 

The only way to break out of a stall is to reduce your angle of attack. Fly by wire can keep a plane from departing, it won't keep you from a stall. (In fact, fly by wire is what is used by aircraft designers to keep planes 'controllable' during stalled flight) A departure is when the aircraft leaves controlled flight, when it rolls off and pitches down, and tumbles out of the sky on its own. You may think that is a bad thing, But it is actually nature's way of taking a pilot who does not know what he is doing out of the picture so that the aircraft can break a stall on its own and save itself. If the computers hadn't kept working the rudder and spoilers automatically to keep the plane from departing, that airbus would have tumbled, and given enough altitude, may have allowed all aboard to live by breaking out of that stall naturally.

 

In science, there is a law called Occam's Razor. It basically states that the simplest solution is probably what's right. What is simpler? For a pilot to think that he is in a mysterious overspeed for 5 minutes when all available indications were that he was too slow? Or for a pilot to see that he is descending and pull back on the stick to climb?

 

Stall protections added to the FBW system certainly can keep a plane from stalling, since they will not allow the plane to exceed the critical angle of attack, thus preventing a stall.

 

A departure in which the plane rolls off is caused by one wing stalling before the other wing does, which is often caused by an aileron deflection. That's why pilots are taught to control the plane using the rudder when very close to the stall speed. An FBW system may certainly help prevent this type of departure, but I don't agree with you that these types of departures are a good thing.

 

A pitch-only departure is certainly a good thing, since it will very quickly lower the angle-of-attack and break the plane out of the stall. If you add in a roll off though the plane is either going to end up upside-down or in a spin. That may have helped the pilots in this case figure out what was going on, but that's a big if. In general I would say though it doesn't help the situation to have a spin or inverted flight added on top of your unexpected stall.

 

I also suspect that the PF reverted to the basic instinct of 'I'm going down, I need to go up!' as an explanation for why he kept pulling on the stick for so long, but it will be interesting to see what the BEA concludes.

Stall protections added to the FBW system certainly can keep a plane from stalling, since they will not allow the plane to exceed the critical angle of attack, thus preventing a stall.

 

A departure in which the plane rolls off is caused by one wing stalling before the other wing does, which is often caused by an aileron deflection. That's why pilots are taught to control the plane using the rudder when very close to the stall speed. An FBW system may certainly help prevent this type of departure, but I don't agree with you that these types of departures are a good thing.

 

A pitch-only departure is certainly a good thing, since it will very quickly lower the angle-of-attack and break the plane out of the stall. If you add in a roll off though the plane is either going to end up upside-down or in a spin. That may have helped the pilots in this case figure out what was going on, but that's a big if. In general I would say though it doesn't help the situation to have a spin or inverted flight added on top of your unexpected stall.

 

I also suspect that the PF reverted to the basic instinct of 'I'm going down, I need to go up!' as an explanation for why he kept pulling on the stick for so long, but it will be interesting to see what the BEA concludes.

 

Do remember that they are flying a swept wing plane. In a swept wing plane, when it does reach that stall breakpoint, she's going to go off on a wing no matter how snappy you are with the rudder. I agree, that a departure carries it's own risks. That is why I made sure each reference to the departure was preceded with words such as 'may.' However, when the person at the stick is the one and only cause of being and staying stalled, then what else do you have left? A departure from controlled flight, and the fall of those chips is the only chance you have left of saving the plane.

Thanks.

 

I'll add to what vc10man said earlier - thanks to everyone for a very interesting, educating and sensible debate!

Rónán O Cadhain, on 18 May 2012 - 03:21 PM, said:

That I'll accept, but that's not what I'm disagreeing with, I'm disagreeing with the mentality that was displayed in the quote that if you have protections you can do as you wish...

 

Rónán.

 

I don't dispute this in any way shape or form Ró, and nor do I dispute the fact that the PF did totally the wrong thing! But (and this is a very big but) to push forward in a stall you first have to identify that you are in that stall. I believe the PF never did that, he was too busy trying to keep the wings level and was overly concerned with an overspeed that didn't exist, even with the stall warning sounding. By the time the aircraft was actually stalling he was in total confusion as to what was happening.

 

I have to say that the stall warning on this a/c seems a little benign. It's almost like a gentle reminder and could go unnoticed if one was totally preoccupied with something else. It needs to be loud and dissonent in order to penetrate the pilot's mind and shock him/her into reacting instinctively by pushing down.

vololiberista

"..it is actually nature's way of taking a pilot who does not know what he is doing out of the picture.."

 

That statement can be understood in more ways than you intended.. :Big Grin: