It's a pity you're not a pilot, Dozy. Then you may undertsand.

Oozlum bird is going round, going round, going round....
 

...sang to the tune of "London bridge"

It's even more basic than QRH. They did not understand what was happening so there was no idea what procedure to follow.

No, it would be wrong. Mere incompetence would not kill them. It was their totally inappropriate reaction that wiped them out.

No, but even as you are introspecting, you might be quite wrong. There were more than thirty crews faced with the very similar predicament. All of them survived unscathed. In no case that could be analyzed there was execution of prescribed procedure recorded. Some crews were so overwhelmed they kept trying to reengage the AP while the stable aeroplane flew itself out of the ice, speeds returned and re-engagement was successful.

Surprise, shock, horror, followed by the panicky reaction.

1 and 2 are elements of basic airmanship, 3 is easily dealt with by making the system so good at introduction it needs no major modifications and upgrades. Guess what: there were no major redesigns of FBW in Airbi since they were introduced and FBW Airbi will make a couple of thousands uneventful flights today.

What type? Pilots scared out of their wits pulling into stall?

It was certainly communicated via FCOM and self-respecting companies trained their pilots in altn law flying during sim sessions.

Severe loss of redundancy as each sidestick now has independent position detection. That infamous DLH incident where roll polarity was reversed in left sidestick with interconnected sticks would left aeroplane with no roll control via sticks at all. As it was, alert first officer disconnected capt's sidestick , took overcontrol and everyone lived on happily instead of cartwheeling into forest just off EDDF 18. My gang insisted that during incap practice we push stick fully outboard and forward, simulating falling on it, so everyone gets practice in taking over the priority. Nowadays if I go lights-out during flight and lean my 220 pounds against the yoke, there is no option for my F/O to just remove my controls from control loop. Something to think about, eh?

Opinionated and unsubstantiated. Far from being sufficient to be taken into account by aeronautical powers that be.

I am a pilot and I know that "I am a pilot" uttered on anonymous forum is worthless.

Fantom:-- don't use the QRH???? Ha that's funny. We look up the damn complicated thing at least twice a flight for 1/ computer resets 2/ OEB's etc..

Linked SS
 

With non-linked SS PNF can hold the SS neutral (or rest his hand on SS pedestal), push the red button and direct take over in critical phases when required.

With linked SS, PNF should remove his hand to not obstruct the SS movement.
When it is required to take over, he now first have to visually locate the deflected position of the stick,
grab the stick and initially fight the other stick input.
(and not forget to push the button to disconnect the adjacent SS)

Valuable time is lost and forward facing philosophy interrupted in critical phases.

In AF447 linked SS could have contributed to another outcome but in the majority of airborne time it is completely useless and in critical phases it can be distracted or even dangerous (as described above)

Guys.

If the SS were linked, PNF would have felt (prolly couldn't see) what the PF was doing.
In the panicky atmosphere of those minutes, words lost their impact.
One pilot cocked up, but if the controls were linked it would have needed two pilots to cock up (and stay cocked up) for the accident sequence to continue.

For pitys sake gents- every dual controlled a/c built (apart from Airbusses) has linked controls.

For a bloody good reason.

Rocket science it is not and I think those who argue against it are bonkers.

I am sorry that I ask, but are you a pilot? Have you operated anything which is classified as airliner? :confused:

Unlinked SS: PF comes in for landing , does the flare pitch wise ok but wings are not level. Me, as PM have to take over by pressing the TO Button. Unfortunately I have no idea now, how much elevator he pulled. So, I have to guess...

The unlinked Sidesticks (and the non moving thrust levers, too) are just downright ridiculous. And so is the QRH, the FCOMs, and and and :ugh:

NIPPI
 

After how many deliveries do unlinked sidesticks (and the non moving thrust levers, too) stop being downright ridiculous?

With 6800 of these planes now in service, I think the design has earned a bit of credibility.

It is not a simple question to answer, because it does depend not only on the 'cutoff airspeed', but also on the behaviour of the airspeed measuring system at high angles of attack. The actual airspeed in AF447 probably never went below 100 kCAS. The indicated airspeed went below 60 kt and even to negative values because at extreme AoA the pressures from which it is derived differed so much from the true static and total pressures. That is hardly 'by design', and other airliners may well be different in that respect.

I would like to see your delivery of your arguments to one of the relatives of the people on board of A447. You could tell them, how good and save this design is - with, after all, 6800 AB FBW flying.

Just do it, after they have been told, that maybe, just maybe, with interconnected SS they might have had a different outcome.

Kids, face it. Airbus went that route because it was more economical and simpler to design non moving Thrust Levers and non connected SS. The present design is not safer - but Airbus (and the relevant authorities around the world) thought it was safe enough.

Whatever the merits of linked vs unlinked SS are, IMHO the facts do not suggest that the outcome of AF447 would have been different with linked SS,

Up to the point where the airplane stalled, the PNF was aware of what the airplane was doing and that the PF was doing it. If he had felt a need to feel the movements of the SS, feeling those erratic movements would not have added anything to his understanding.

After the airplane stalled, the PNF's understanding of that fact was no better than the PF's and his response to the excessive rate of descent was no different from the PF:

02:11:21 But we've got the engines what's happening?
02:12:13 We're pulling
02:13:40 Climb, climb, climb, climb.

fantom
 

The core issue?
BEagle got it right first time.
Plus at all times during the event, the crew had two fully functioning engines, a standby horizon and compass, and a groundspeed readout?????

I'm quite sick and tired of people who should know better blaming Airbus for this crash. Had there been a different crew flying that night, they would have landed safely. I've said before and will state again:-
a. You don't flying a heavy 'plane (close to coffin corner, at high altitude) into a storm
b. You set up the radar at top of climb
c. You must know the memory items for loss of airspeed drill (and others)
d. You must understand what super-cooled water is and how it can affect your 'plane.
e. As someone pointed out, even if they did nothing, the aircraft is stable enough to right itself. However if you deliberately hold back pressure when you shouldn't, well.............
f. There is no harm in circumnavigating a storm, even if it means making a fuel stop. That's why the pay pilots big bucks, to be SAFE not stupid

This a very sad accident that should never have happened, and I hope by now most of you have learned some valuable lessons from it. I flew the A320 for over 10 years and never encountered any serious problems handling it. If you don't understand your airplane, don't try to fly it. Find something else to do with your life..
Thermostat.

At 40 deg AoA the airplane is still stalled so the warning has to keep going.

Such assessment on linked SS is inaccurate.
For the PM the thumb and one finger around the base of the SS would be all it takes to know exactly how the PF is soliciting the other SS.
Valuable time is certainly not lost, but gained.

Certainly not useless, distracting or dangerous, but a pure mine of information.
Much improved Situation Awareness.

It's a perfectly good and safe design, provided it isn't being used by people who haven't a clue about what they're doing, who don't have a disciplined flight deck environment and who don't even have a positive handover/takeover control procedure.

PILOT ERROR cause the A447 accident - nothing more, nothing less.

I dont think anyone disagrees with you. It is pretty clear the accident was due to pilot error. The comments advocating linked sidesticks are about reducing the posibilty of similar accidents by making the controls less susceptable to pilot error, less susceptable to training deficiencies, less susceptable to failures, such a pitot tube blocking, causing confusion etc.

Even in a "perfectly good and safe design" there is always room for improvement.

You have to wonder though, if it's all the 'improvements' that have got us here in the first place. To a certain extent anyway.

AlfaZuluRomeo is correct. According to the Accident Report, a reversion to Alternate Law 2B was caused by airspeed "inconsistency" and this mode did not inhibit the THS Autotrim. The THS autotrimmed to 13 deg nose up in response to the PF's aft stick control movements and remained at that value due to the AOA averaging 35 deg during the descent until impact with the sea.

Unusual Attitude Law Reversion was never activated as none of the discrete values were reached.

We went through this in the Tech Log threads - how can the warning keep going if the data required to provide its correct operation is unavailable? You can't just latch it on, because that runs the risk of the warning continuing to sound after the aircraft is out of the stall regime and causing confusion that way.

Obviously you don't latch it on and forget it.

If all the vanes are flopping around in the breeze regardless of the speed, for goodness sake the aircraft must be in a non-flying ie stalled condition. Make the stall warning sound until it is flying again, not switch off below 60KIAS because some boffin thinks "that can't happen". This is not a hard concept to grasp.

For one thing, it's very hard to detect a "flopping around in the breeze" situation using either analogue or digital means. For another, you're talking about a single failure mode - it might work in an AF447-type scenario, but it won't work in other scenarios - say, if the vane itself fails structurally, or if the cable connecting the vane to the transducer unit fails for whatever reason. This is one of the oldest conundrums in engineering - making sure that an alteration that solves one issue doesn't inadvertently create more problems (as Boeing have been experiencing with their battery issues).

Additionally, this isn't an issue of 'some boffin think[ing] "that can't happen"'. The AoA vanes were supplied with a specification that said they will not function correctly below 60kts IAS - therefore the *aero engineers* wrote the systems specifications to disregard output below that value. According to A33Zab, Boeing's engineers wrote the same specification below 50kts IAS.

One approach to cockpit warnings is that it is better to have a warning, and be able to override it, than not have the warning. Dozy, I understand what you are saying based on the spec, and as we noted previously, you can use a weight on wheel switch to inhibit the stall warning when on the ground.

We have discussed this over and over, and the hamster is getting awfully tired. :cool:

Dozy,

I'm not a systems expert but how about, in the case of loss of all AoA data, the stall warning system retaining the last valid value of AoA until that parameter is valid again? There also should be an ECAM message suggesting selection of FPV to allow comparison of FPA and pitch attitude.

@LW_50:

I get what you're saying, but this isn't a case of Stall Warning being inhibited, it's a case of the data being unusable. You can override the SW, but if the failure is of a nature whereby it comes straight back on, it could cause problems.

@HN39:
Retaining the last valid value can cause the same issue - sure, in a scenario like AF447 the values can come back, but in other failure scenarios (damaged vane or cable) SW could be stuck on and cause problems, because the value will never be valid again.

And not having the warning can cause problems. See AF447. (Though that wasn't their only problem, not by a damned sight.)

It's a lose lose situation, other than the fact that there are multiple AoA probes on the A330. We went over that as well. We could even run the hamster for a while on the AoA indicator in the C/P ... but that got us nowhere other than "who uses it?" "if they aren't scanning primary, what else won't they scan?" and "it could cause problems."

Nothing new here, and that poor hamster is exhausted. :p

This all may shed some light on why the general training standard is prevent stall in large transport aircraft. Doing so renders a few of these problems moot.

10000 feet a minute is a good breeze enough for all AoA probes to indicate a pretty similar value. If the probes mechanical limit is at 85 deg I believe 40 to be in their range of operation.

The stall warning has to keep going.

Agreed - however...

The AF447 scenario was not a case of the Stall Warning suddenly disappearing after sounding briefly, the warning sounded for almost a *minute* with no apparent acknowledgement by the crew. The AoA readings became invalid because the aircraft had been pulled into an attitude so extreme that the sensors could no longer keep up.

This is what would be considered in engineering terms an extreme edge case, and thus far it has happened precisely once. If a technical solution was simple to implement without serious knock-on effects, it would be done - but the fact is that it is an extremely difficult problem to solve.

[EDIT : Additionally, while it may seem logical to assume that a warning in the face of uncertain data is better than none, I can't help but think of Birgenair 301 - where the captain fixated on a false Overspeed warning to the exclusion of all else and ended up stalling the aircraft. ]

Well, arguably that training standard was at the root of the problems because it was implemented at the expense of stall recognition and recovery, and as such the standards have been changed in the wake of the accident.

At the end of the day, we're not talking about a stall warning that stopped sounding in an unreasonably short period of time after stall was initiated, we're talking about an aircraft that was pulled even deeper into the stall while the warning was sounding - until it was so far outside the flight envelope that it exceeded even the theoretical limits of instrument behaviour.

Gee, a weight-on-wheels switch is too damned hard to wire up. Insanely difficult technical obstacle. You just went from "you only have to follow the numbers on the spec" to 'it's too hard." Further comments :mad: as I am done with this hamster abuse.

How would a WoW switch affect the fact that the sensors don't work in the air if certain parameters are exceeded?

DozyWannabe,

The stall warning system looks at three values of AoA from three independent sensors. It sounds a warning if the highest of the valid AoA values exceeds the threshold defined by the highest of the valid airspeeds. If I understand correctly, the system can loose any two of those values and it will still operate on the single remaining one. In other words, the system is strongly biased towards giving a warning when required, at the detriment of unwanted operation. Yet, when all three AoA values suddenly disappear, the last valid value being 41.5 degrees, the system just goes silent. No warning, not even a message on the ECAM.

Against my better judgment:

The decision to accept or reject the signal and be silent at <60 kts is what is being pointed to as a design oversight. This isn't new. To avoid spurious warnings at low speed on T/O or Ldg with a WoW avoids spurious warning. Any other time, weight off wheels, that you approach those values, the warning will have already been going off long before the "threshold" value of 60 kts.

HazelNuts covered the rest.

See also Confiture's point about air flow when falling at 10,000 fpm.

@HN39:

I'm sure you're correct. However we're talking about a situation whereby all three airspeed sensors (pitot tubes) are being fouled by disturbed air as a result of extreme AoA.

You're also absolutely right that implementing a warning - either visual through ECAM and/or aural - that AoA is no longer valid would be do-able, but it's then incumbent on the crew to understand what that means.

@LW_50:

I'm not disputing what you're saying - but the <60kts limit was not implemented purely for the purpose of avoiding spurious warnings on the ground, it was also because the data from the vanes is unreliable in the air in that scenario. CONF iture is working on the assumption that the airflow from the descent would be enough to generate a valid reading, but I'd need to know what the specification said to know whether that was true or not.

How about Vmo? :}

It makes sense that the vane is unreliable below 60 KTS, but I'm not seeing how you could have a false stall warning at that speed (absent weight on the wheels). Since the aircraft would be stalled, any warning would be accurate.

Unreliable data might mean that the alarm would not always sound below 60KTS even if the aircraft was stalled. Apparently the designers decided a stall warning that would never work below 60KTS was better than one that would sometimes fail below that speed.

No guarantee that the aircraft would be stalled if the <60kts reading was false.

I don't think the designers made a conscious decision in that regard - it's so far outside the flight envelope that it probably wasn't considered at the time.

Since no aircraft certified for airliners can fly below 60 knots I can see why stall warning is inhibited. If the crew can't figure that out it is their problem. We need smarter pilots. I don't want to point any fingers but sometimes pilots do not act as pilots, they just react to stall warnings and don't think.

Pretty sure the AoA sensors can very well keep up at 100 kt.

To clarify that statement I just wanted to say AF447 pulled up into a full stall for no reason. They were probably taught the Airbus wouldn't stall but it did. It had different laws and what they did was very stupid but they did what they were told to do by some instructor probably. I have been told very stupid procedures by instructors that never fly an airplane so ignore them. Be careful about what they tell you. They just teach, they don't fly.

In terms of the horizontal component of travel yes - I was more concerned with the vertical. The aircraft was oriented such that the vertical airflow was fouling the pitot tubes - I suspect it would also have been sufficient to give false AoA readings.

Of course, this is all speculative as we don't have the spec to hand. I also think we're splitting hairs at this point, because we can't prove one way or another - and the last thing I want to do is give the hamster wheel another push.

Quote:
Apparently the designers decided a stall warning that would never work below 60KTS was better than one that would sometimes fail below that speed.
Dozy, I'll agree with that statement, however the whole loss of stall warning below 60 knots was a conceptual design error.

Airspeed and AOA are each independent measures of aircraft performance. To force AOA to become dependent on airspeed is an error.

If you will recall, I ran some experiments on a surplus airline type AOA vane sensor, and the thing came alive below 20 mph.

There is no reason to suspect that there was inadequate dynamic pressure to activate the vanes on AF447, nor is there reason to suspect that the location of the sensors while at that high AOA would subject them to flow reversal or turbulence. The worst that could happen would be that the AOA would exceed the range of the sensor, but at least they would be at the limit in the proper direction.

This shut down of the stall warning system was not without consequence. It deprived the captain of an essential piece of information when he attempted to size up the situation upon arrival back on the flight deck (Remember? Stall warning shut down almost co-incident with his arrival on the flight deck).

The question I have now is, has the conceptual design error been quietly corrected?

Dozy,

I agree with you about the designers --there was no reason for them to foresee a need for a stall warning below 60KTS. And if they had, presumably they would have chosen a technology that was reliable below that speed.

But if you're saying the stall warning should be suppressed below 60KTS because the airspeed data might be wrong, I don't agree. No matter what the pitot tubes are reading, the airspeed is either over 60KTS, in which case the AOA sensor is reading correctly, or it's below 60KTS, in which case the aircraft is stalled regardless of what the AOA sensor says.