Afriqiyah Airbus 330 Crash

[Capn Bloggs]

Originally Posted by Dozy

To my mind the advantage of a trimmable stabiliser over tabs in a technical sense has to do with command authority - a trimmable flight surface can potentially have a far greater degree of pitch authority in the event of an elevator system failure or jam than a trim tab on the elevator itself. I don't think any airliner has used tabs over surfaces for trim since the days of the B707 and DC-8.

It's got nothing to do with pitch authority. One cannot "fly" an aeroplane, in the normal sense of the word, using the horizontal stabiliser alone. It doesn't react fast enough (unless it's an all-flying stab like a fighter). That's why there is an elevator surface hanging off the back of it, connected to the stick.

Originally Posted by Dozy

You'd have to ask an aerodynamicist to be sure, but I'm confident that the difference would be negligible - to say the very least!

Negligible? How about massive? Good aerodynamics equals good economics, Dozy. When I take off, my stab trim is around 5°. In the cruise it is zero. If I had a fixed stab, the drag would be huge. The compromise, setting a fixed stab at 2.5°, would be crazily draggy in the cruise and would require a massive elevator for takeoff and landing.

[DozyWannabe]

Originally Posted by Capn Bloggs

It's got nothing to do with pitch authority. One cannot "fly" an aeroplane, in the normal sense of the word, using the horizontal stabiliser alone. It doesn't react fast enough (unless it's an all-flying stab like a fighter).

Most trimmable horizontal stabs on modern airliners are all-flying, though. In fact the last-ditch control law on the Airbus FBW types is MAN PITCH TRIM ONLY, in which the pitch and rudder trim are the only way (other than differential thrust) to control the aircraft.

I've asked my friendly local aerodynamicist about the drag question - hopefully I'll get an answer shortly.

[Capn Bloggs]

Most trimmable horizontal stabs on modern airliners are all-flying, though.

No they are not. I did say "in the normal sense of the word". That does not mean pitch-trim-only pitch control. The pilots cannot control the stab as if it were an elevator. My understanding of the "emergency" pitch control on the earlier Airbus is pitch TRIM, not "pull back on stick and nose goes up". In other words, manually spin the pitch trim wheel (just like you'd have to do if it trimmed full nose up and then you stalled/lost normal law).

[PJ2]

The term "all-flying" refers to a stabilator, like the L1011 design. The entire horizontal stabilizer moves with the control column and also independently trims the aircraft either by manual or autoflight control. AFAIK, the Lockheed was the only transport type with this design.

The term "all-flying" means nothing because horizontal stabilizers have been trimmable since the dawn of the jet age.

[Clandestino]

Originally Posted by Cpn Bloggs

Codswallop. What don't you understand about:

the automatic trim system, which relieves the pilot of any actions to trim the aeroplane, was no longer available. In the absence of preparation and anticipation of the phenomenon, the habit of having the automatic trim system available made it difficult to return to flying with manual trimming of the aeroplane.

Just when you need it most, the aeroplane behaves totally differently to normal.

This excerpt was taken from BEA's report on fatal accident of A320-232 D-AXLA near Canet-Plage on Nov 27 2008. Aeroplane was on post maintenance test flight, during which it was planned to test high AoA protections. Due to ATC restrictions, test could not be made at high altitude so the crew decided to perform it as they were returning to airport. No calculation of speeds at which protections would become active was performed so as the aeroplane decelarated at 3000 ft, no one noticed that displayed low speed cues on PFD were unrealistically low or that FMGS displayed "CHECK GW" - indication that there is discrepancy between speed , AoA and FMGS inputed weight. Protections did not activate because 2 out of 3 Aoa probes froze and gave constant and false AoA output. They froze because someone pressure washed the aeroplane without using protective covers.

So yes, badly maintained aeroplane behaves totally differently to normal, it's not something every Airbus does and I expect furious denial that such a thing was even remotely suggested. Freezing of AoA probes was something properly conceived and executed flight test should have caught.

[Owain Glyndwr]

Dozy,

Not sure what you mean by friendly local aerodynamicist, but since I qualify on two out of the three I'll stick my oar in

You are wrong I'm afraid -well half wrong anyway. Trimming using the whole HS (to a smaller deflection) is going to be more efficient than just using elevators on a fixed HS. That said, there is a side benefit from having a trimmable HS in that it leaves the whole range of elevator deflection available for manoeuvre.

I'm afraid that using trim tabs on the elevators (or other control surfaces) is before even my time .
But as I understand it, their use was to trim out the hinge moments associated with the elevator deflection needed to trim the aircraft. This removed any standing trim load on the stick so the aircraft could be flown hands off. The trimmed drag would then be much the same as that from deflected elevators on a fixed HS.

[lederhosen]

I originally raised the similarities between the Air France incident and the Afriqiyah crash: early morning arrival, dangerously bad approach and mishandled go-around on an airbus widebody. I also used the phrase Airbus way of flying.

Dozy asked me what I meant by this and linked it to Airbus procedures, which was not what I was talking about, as I pointed out in my response. Clandestino then picked up on the word automation which he equated to autoflight, which is not correct.

Automation is the technique of making an apparatus, process or system operate automatically (to take a widely available definition). The autotrim system is clearly therefore an example of automation. As has been pointed out in direct law it stops working. So there is a link between control laws and level of automation. Dozy's definition that automation only applies at the level of FMC/FMS is twisting things to back up his view of the world. The fact that Honeywell produce FMCs for both Airbus and Boeing is also hardly evidence that the aircraft are operated the same way.

Pprune discussions regularly split into Airbus versus Boeing camps. People are often quick to rubbish the views of anyone who disagrees. Things that were never said are misattributed and used as evidence that those with different views do not know what they are talking about. I will be astonished if there is any kind of grudging acceptance of this very plain fact.

Nevertheless it is still a valid question as to whether this type of incident or accident occurs more frequently on the Airbus. I am not aware of any crashes for instance on the 777 caused by this kind of thing.

[DozyWannabe]

All - Regarding my mistake in terminology ("all-flying") and drag - thanks for the heads-up!

Originally Posted by lederhosen

Automation is the technique of making an apparatus, process or system operate automatically (to take a widely available definition). The autotrim system is clearly therefore an example of automation. As has been pointed out in direct law it stops working. So there is a link between control laws and level of automation. Dozy's definition that automation only applies at the level of FMC/FMS is twisting things to back up his view of the world.

I was actually very careful to qualify my statement, which was "Autotrim is *not* automation in the traditional sense of aviation terminology because it does not in and of itself make and effect flightpath decisions". Put another way, I choose - based on what I've read and been taught - that the distinction between the two is whether one is hand-flying or under autopilot/autothrust control.

In the FBW Airbus types, a hand-flying pilot is still hand-flying if the autotrim is active (which will be the case for almost all line pilots flying the types for the duration of their careers). Sure, autotrim is a form of automation in the fundamental sense of the term, but so is the yaw damper system which has been around for much longer. Yaw dampers have failed, in some cases leading to the loss of aircraft - but I can't think of a case where such an incident was considered an example of encroaching automation dependency.

[Clandestino]

Originally Posted by lederhosen

whether this type of incident or accident occurs more frequently on the Airbus.

Compared to Boeing FBWs, it does. I know you won't be able to resist this bait.

[DozyWannabe]

With the caveat that there are fewer T7s than A330/A340s even before one takes into account the number of A320 variants, and that Airbus sold their types in more territories with a marginal safety record than Boeing did the T7. This makes comparison of raw hull-loss statistics a misleading metric.

This isn't an A vs. B issue for me - I only engage on more Airbus threads because I know the technology better than I do that of the T7.

[lederhosen]

I cannot disagree with anything in the last two posts. Although the difference in numbers between 777 and A330/340 is not orders of magnitude, around about 1100 versus 1300 delivered.

I like Airbus and what they are trying to do. The irony is that when basic flying skills are most required they seem less in evidence after a while of the Airbus way of flying.

[DozyWannabe]

Honest question - what is your definition of "the Airbus way of flying"?

Judging by the evidence at hand, I'd say that accidents resulting from loss-of-control seem to be very much type-agnostic.

[lederhosen]

I refer you back to to post 1521 where I attempted to convey some of the issues. At the man machine interface level the Airbus is more than just a little different from conventional jets. If you are not convinced by my words let me quote from the Airbus Flight crew operating manual.

Direct law

The sidestick is directly coupled to the controls via the computers, but without any of the stabilization feedbacks. In effect this law turns the aircraft into a conventional aircraft.....

So Airbus themselves are pointing out that their aircraft are different from conventional aircraft and go on to warn pilots about the consequances of missing protections etc.

The aim of the technocrats to deskill flying was clear, paraphrasing one of them, it was to design an aircraft his doorman could fly. However what they also did was create a machine that can be extremely complicated in abnormal situations and where apparently experienced pilots seem to do inexplicable things.

[DozyWannabe]

Originally Posted by lederhosen

The aim of the technocrats to deskill flying was clear, paraphrasing one of them, it was to design an aircraft his doorman could fly.

If you believe that, it's because you've only heard one side of the story. There was a pilot engineer group included at every stage of design and development (including, and later headed by D.P. Davies' successor), and nothing passed muster without their approval. The intent was never to deskill flying, it was simply to provide an extra layer of safety using technology that had been used in the space programme and military aircraft for over a decade before the A320 was even proposed.

BZ's infamous "concierge" comment was nothing more than an off-the-cuff remark - his role in terms of leading the project was largely managerial and later sales-related.

However what they also did was create a machine that can be extremely complicated in abnormal situations and where apparently experienced pilots seem to do inexplicable things.

That's true of any aircraft though, no matter the level of technology and/or automation available.

[Clandestino]

Originally Posted by Lederhosen

I know a lot of Airbus pilots and most are extremely positive. What they say is that their aircraft are on a day to day basis very agreeable to fly. However when something abnormal happens they can be more complicated than a Boeing.

So say anonymous friends of anonymous poster. AS these are anonymous forums...

Originally Posted by Lederhosen

The sheer amount of information available and the different levels of automation, for example control laws makes them that much more complex.

Unsubstantiated claim. T7 also has FBW degradation modes; they don't call it alternate and direct law but rather secondary and direct mode. It is simple and straightforward, just like in the Airbus. For pilots, that is.

Originally Posted by Lederhosen

A sim session involves endless reading.

No different from other modern airliners.

Originally Posted by Lederhosen

On a 737 you can switch off all the automatics and mostly you know what you have.

Same as on the bus but then you have to know your aeroplane and for that you need to read and understand FCOM, not just complain "oh, it's sooo complicated!".

Originally Posted by Lederhosen

It does not have to be that way.

Now it's certified that way, it does.

Originally Posted by Lederhosen

The fact is that it seems that there are some long haul guys at least, who have very little opportunity and possibly inclination to practice.

Same as on the other long haul aeroplanes.

Originally Posted by Lederhosen

If you get one or two landings a month often at five in the morning are you really going to be as current as an Easyjet captain doing ten times as many landings a month?

If you get one or two landings a month, you certainly won't be doing Easyjet's captain job. Since we have no crashes of long haul widebodies on daily basis, point is moot.

Originally Posted by Lederhosen

There is no doubt what Airbus intended and there are doubtless countless lives saved we will never know about because of all the safety features that Airbus have built in.

Those who want and need to know, have the way to find out. Incident reports. Safety bulletins.

Originally Posted by Lederhosen

However the issue of manual flying currency is one that Airbus is aware of as other threads such as the one about the A350 demonstrate.

Same as on the other aeroplanes.

Originally Posted by Lederhosen

The end result is a risk of automation dependancy

Same as on the other aeroplanes.

Originally Posted by Lederhosen

The Air France captain's desire to reengage the automatics so soon after an unusual attitude recovery could certainly be interpreted that way. The Afriqiyah crew flying a serviceable aeroplane into the ground clearly demonstrates they were not fully in control or as I put it in my earlier post they were outside the loop.

And we are to believe that since both occurences happened to 330, well then it must be Airbus fault?

Originally Posted by Lederhosen

Although the difference in numbers between 777 and A330/340 is not orders of magnitude, around about 1100 versus 1300 delivered.

That's not complete argument that was made. Let me help you:

Originally Posted by Dozy Wannabe

there are fewer T7s than A330/A340s even before one takes into account the number of A320 variants, and that Airbus sold their types in more territories with a marginal safety record than Boeing did the T7. This makes comparison of raw hull-loss statistics a misleading metric.

Originally Posted by Lederhosen

I refer you back to to post 1521 where I attempted to convey some of the issues.

Though issues were successfully conveyed, I find them somewhat lacking in plausibility.

Originally Posted by Lederhosen

Alternate law

The sidestick is directly coupled to the controls via the computers, but without any of the stabilization feedbacks. In effect this law turns the aircraft into a conventional aircraft.....

Alternate law is still flightpath stable on any Airbus, it is definitively not direct coupling of stick to controls. This quote is stupendously wrong.

Originally Posted by Lederhosen

So Airbus themselves are pointing out that their aircraft are different from conventional aircraft and go on to warn pilots about the consequances of missing protections etc.

In your post, that is.

Originally Posted by Lederhosen

The aim of the technocrats to deskill flying was clear, paraphrasing one of them, it was to design an aircraft his doorman could fly

Sales hype contradicting the introduction of every Airbus FCOM but don't let the facts ruin the good libel.

Originally Posted by Lederhosen

However what they also did was create a machine that can be extremely complicated in abnormal situations and where apparently experienced pilots seem to do inexplicable things.

Same as the other passenger transport aeroplanes.

[Capn Bloggs]

Bit of trolling going on here.

[lederhosen]

I agree with you Cpt Bloggs. Clandestino your over the top effort to persuade us that you are right and anyone who has a different opinion is talking rubbish reminds me of the time you attempted to argue in favour of the MD11.

Just to make it clear I am no way anti Airbus. I have merely raised the issue that the combination of long haul, back of the clock flying and the Airbus man machine interface seem to have occured in some notable recent incidents and accidents.

I did however make a typo (which I have corrected) in my previous post, when I wrote Alternate law instead of Direct law. If you are an Airbus pilot you can find the paragraph in FCOM3 Flight Operations, supplementary techniques, flight controls, abnormal control laws, general (with acknowledgement to Airbus).

I am not saying that Airbus overall are any more dangerous than comparable aircraft (unlike the MD11...cue incoming from Clandestino), just hypothesising about some issues obvious in the Afriqiyah accident and elsewhere, which seem to offer further opportunity for improvement. I do not expect everyone to agree, but lets discuss this reasonably.

[Turbine D]

Originally Posted by lederhosen
I agree with you Cpt Bloggs. Clandestino your over the top effort to persuade us that you are right and anyone who has a different opinion is talking rubbish reminds me of the time you attempted to argue in favour of the MD11.

IMO, the problem is some people post personal opinions as if they were absolutely factual information, supported by published data, when in fact, they are often not supportable or factual. It is not a matter of over the top persuasion at all.

Originally Posted by Capn Bloggs
Bit of trolling going on here.

Definition of "trolling": Submit a posting with the intent of inciting an angry response. I would suggest this is not the case at all, it is simply pointing out fact from fiction (opinion) to the original poster who portrayed fiction (opinion) as fact.

[DozyWannabe]

Originally Posted by Turbine D

IMO, the problem is some people post personal opinions as if they were absolutely factual information, supported by published data, when in fact, they are often not supportable or factual. It is not a matter of over the top persuasion at all.

Indeed. In fact I'd say that a far bigger issue is elements of both sides of an argument being unwilling to listen to and appreciate the arguments of the other side when it comes to opinion, then becoming so entrenched in defending that position that they hold it tenaciously and willing to give no quarter even when presented with hard evidence.

Definition of "trolling": Submit a posting with the intent of inciting an angry response.

To be more precise in terms of the original definition, it's about inciting as many angry responses as possible, then drawing those who make said responses into an off-topic argument that can continue for pages and pages. It's about attention-seeking, and in fact the term is based on the verb "to troll" (as in fishing terminology) more than it is the noun "troll" (meaning an aggressive, ignorant mythical creature).

[lederhosen]

Lets just agree to differ. As a current jet captain (who gets to jumpseat on the bus from time to time and has a smattering of experience in workplace design) I believe I have an informed opinion. This is after all a professional pilots rumour network. Most of what is posted is opinion. What the last two gentlemen posted is their opinion (to which they are entitled).

I attempted to answer a question from Dozy in good faith. Clandestino deconstructed it in a way that made me smile. Not all he says is unreasonable. But I think most people would accept that it is a bit over the top.

Boiling it down to essentials, as a professional pilot I consider the man machine interface in the Airbus to be different from conventional aircraft (fact). Airbus say it is so and and frankly it is hardly a blinding insight. I have hypothesized about the role this played in some recent incidents/accidents (opinion).

I would be delighted if we could move on.