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AF 447 Thread No. 12

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AF 447 Thread No. 12

Old 27th Feb 2017, 11:47
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Quote from Concours77 [my emphasis]:
"I asked Owain Glyndwr at one point why the graph in the report of the THS movement looks "smooth"? Yet the graph of the stick trace looks anything but? The trace is full of bumps, up and down...."

Here is a video of an A320 co-pilot handling the sidestick on what is probably a fairly average day:

https://www.youtube.com/watch?v=vBuoA9qkKi4

(Several other similar videos are available on line.) The aircraft is presumably in Normal Law, but the pilot is consistently over-controlling the sidestick; behaviour that I often saw from the jump seat during many years of line-checking on the A320. I doubt that the pilot concerned was even aware he was doing it.

In AF447, the control laws were C* in pitch, but Direct in roll. That makes for a bad combination, because a lot of firm** movements may have to be made to keep the wings level, while only small movements are appropriate in pitch. With the Airbus sidestick it is more difficult to avoid roll commands affecting pitch commands (and vice-versa) than it is on the traditional column/control-wheel combination.

** [EDIT, in deference to comment by IcePack - below]:
(larger than those needed for pitch)

Last edited by Chris Scott; 27th Feb 2017 at 17:00. Reason: See **
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Old 27th Feb 2017, 12:45
  #1382 (permalink)  
 
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I wouldn't recommend firm control inputs at high altitude in direct law in roll either. Direct roll law rate of roll is something like 60deg a second. (Not published)
As I have said before it is criminal that the simulators do not simulate control responses at high altitude correctly. (Sims fly the same at 150 &350)
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Old 27th Feb 2017, 14:55
  #1383 (permalink)  
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Icepack, I do agree with your observation that one should be gentle with the controls at high altitude. One should be gentle at all times with transport aircraft! It was this same, sage advice that D. P. Davies offered in Handling the Big Jets, (editions 1967 - 1971). I believe that most experienced pilots on these aircraft know this and respond appropriately.

"Criminal" may perhaps be a bit strong regarding simulator fidelities. Also, a lot has changed in simulation over the last decade including heightened fidelity for stall performance.

We have to remember that prior to AF447, there were 31 other UAS events on A330s and every one was a log-book entry.
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Old 27th Feb 2017, 14:56
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Machinbird

Re fear, flight.

"02:10:06 (Bonin) I have the controls.
02:10:07 (Robert) Okay."

Within one second of AP quit, Bonin has acted correctly, and was acknowledged by PNF Robert.

He then quickly input stick back, and roll left. The record as regards Roll shows an inheritance of roll right, and an "over control" left. In the ensuing seconds, he established roll stability, and the aircraft had started to climb....At this point, Bonin "owns" what is to follow.

This should rebut any discussion of paralyzing fear, the flee fight syndrome, or other theories indulged to establish abnormal reaction/behaviour?

As to startle, Bonin had contacted the CC and told them "you should be careful".
Startle implies he was unprepared for the loss of AP and the consequent alarms.
His actions on the record would confirm, at least at this stage, that entertaining a discussion about physiology and fear is not supported?

Next? When did the crew recognize and acknowledge the cause of the problem, and the aircraft's response to it?

Last edited by Concours77; 27th Feb 2017 at 15:29.
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Old 27th Feb 2017, 15:13
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Are we back to explaining what an instrument scan is?
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Old 27th Feb 2017, 15:43
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Quote from Concours77:
"This should rebut any discussion of paralyzing fear, the flee fight syndrome, or other theories indulged to establish abnormal reaction/behaviour?"

It might at first seem to rule out the startle factor, but I can assure you that the sudden, unwanted sound of the "cavalry charge" (audio signal of AP disconnect) is not conducive to relaxation on a dark night. Add to that some turbulence, a partial loss of primary flight-instrumentation, and ECAM warnings, and none of these physiological/psychological factors can be ruled out.

The sidestick needed to be used with the utmost care, as others confirm above. Fear, or even tension, make that more difficult. The muscles of the forearm and hand may tighten, which could well have caused the PF to pull on the sidestick unintentionally (see my previous post), particularly if he was preoccupied with trying to keep the wings level in unfamiliar, roll-direct law.
Another possible difficulty controlling the sidestick would have arisen if the PF' s seat was too far back, or if his sidestick armrest was not deployed correctly.

The bottom line is that this crew lost situational awareness, or they would never have allowed the aircraft to climb 2000 feet without specific comment. That alone suggests mental processes associated with fear and/or overload. During that climb, they were not sitting there drinking coffee or reading a magazine.
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Old 27th Feb 2017, 15:43
  #1387 (permalink)  
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Lonewolf_50;

Re explaining scan, ;-)

We may be chatting with & explaining to a new generation who were just starting out eight years ago or otherwise too young to remember the details of AF447 and are newly-curious.

I think the twelve AF447 threads are a goldmine of thought and, like Davies, are all well worth spending the time reading through - they're an informal "book", rabbit-trails and all, on primary topics for aviators like the one you've touched upon.
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Old 27th Feb 2017, 16:32
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Concours77
This is not intended as a put down, but you are lacking sufficient aviation experience to properly understand the elements of the AF447 accident. You have almost certainly not hand flown at night in the feathery tops of a complex cumulus based storm system looking at your radar screen for indications of bad areas, with St Elmo's fire flickering around your windscreen with occasional larger balls of discharge forming on parts of the aircraft ahead and alongside of you, while listening to the screech of static discharge in your headset. There are many experiences in the corners of the flight envelope you have not seen. Your mental picture of the events of AF447 is too glib.

In the ensuing seconds, he established roll stability,
This statement ignores the fact that it took almost 30 seconds of frightening overcontrol to establish roll stability, and what enabled that stability was the reduction of roll gain resulting loss of airspeed..
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Old 27th Feb 2017, 16:49
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Would you classify that thirty seconds as "jet upset"? If so, I would agree, and acknowledge that as the beginning of the Loss of Control? Especially so if the focus on Roll recovery cost airspeed and Pitch awareness? Where was FO Robert? Aside... Was Roll ever effectively managed? Captain remarked on it....

Back to interface of man and machine...
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Old 27th Feb 2017, 17:09
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"Icepack, I do agree with your observation that one should be gentle with the controls at high altitude. One should be gentle at all times with transport aircraft! It was this same, sage advice that D. P. Davies offered in Handling the Big Jets, (editions 1967 - 1971). I believe that most experienced pilots on these aircraft know this and respond appropriately. "

Does that still apply, when many younger pilots of FBW transports now have no experience of hand-flying any jet at high altitude, even with a fully-functional EFCS ?
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Old 27th Feb 2017, 17:16
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Originally Posted by Concours77
When did the crew recognize and acknowledge the cause of the problem, and the aircraft's response to it?
Shortly before impact, it seems. If you have read the transcript in the BEA report, Captain DuBois recognized that something had gone horribly wrong with his "impossible" at 02 12 43,8 on the CVR. As they went through their problem solving efforts, clear identification of the problem seems to have eluded the crew.
Extracted from the CVR Trascript provided in Appendix 1 to the report
2 h 10 min 03 2 h10 min 04,6 Cavalry charge (autopilot disconnection warning)
2 h 10 min 06,4 Bonin | I have the controls
2 h 10 min 11,0 SV | stall
2 h 10 min 22,1 Robert | alternate law protections- (law/low/lo)
2 h 11 min 01,2 Robert | Above all try to touch the lateral controls as little as possible eh
2 h 11 min 25,7 Robert | Do you understand what’s happening or not?
2 h 11 min 32,6 Bonin |(…) I don’t have control of the airplane any more now
2 h 11 min 34,7 Bonin | I don’t have control of the airplane at all
2 h 11 min 42,5 DuBois | Er what are you (doing)?
2 h 11 min 48,2 Robert | We lost all control of the aeroplane we don’t understand anything we’ve tried everything
2 h 12 min 23,0 Dubois | The wings to flat horizon the standby horizon
2 h 12 min 43,8 DuBois | (…) it’s impossible
2 h 13 min 39,7 Robert | Climb climb climb climb
2 h 13 min 41,2 Bonin | But I’ve been at maxi nose-up for a while
2 h 13 min 42,7 Dubois | no no no don’t climb
2 h 14 min 05,3 DuBois | Watch out you’re pitching up there
2 h 14 min 06,5 Robert | I’m pitching up
2 h 14 min 06,5 DuBois | You’re pitching up
2 h 14 min 07,3 Robert | I’m pitching up
2 h 14 min 07,3 Bonin | Well we need to we are at four thousand feet
2 h 14 min 23,7 Bonin | (!) we’re going to crash
2 h 14 min 24,2 Bonin | This can’t be true


Note: there is quite a bit more on the transcript, but I cut these bits out to illustrate from initiation to almost impact some of the what they were saying as they tried to resolve their problem.

Last edited by Lonewolf_50; 27th Feb 2017 at 18:25.
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Old 27th Feb 2017, 17:21
  #1392 (permalink)  
 
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Originally Posted by IcePack
I wouldn't recommend firm control inputs at high altitude in direct law in roll either. Direct roll law rate of roll is something like 60deg a second. (Not published)
As I have said before it is criminal that the simulators do not simulate control responses at high altitude correctly. (Sims fly the same at 150 &350)
However it could be quite easy to compute an approximate value of this roll rate.
Only "confidential" input required is aileron deflection obtained with full lateral sidestick in direct law. However, it should be the maximum deflection of both ailerons as well as roll spoilers (someone might be able to confirm/infirm this).
The full deflections are easily obtained if you have the real aircraft in front of you (which pilots have).

Then it's just an equilibrium between Clp*pb/2v and Cldl*dl
As I was saying on the ATPL theory questions topic, the TAS will increase the roll rate, so 450KTAS must give a very high roll rate.
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Old 27th Feb 2017, 18:42
  #1393 (permalink)  
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Originally Posted by Chris Scott @ 27th Feb 2017, 10:09
Does that still apply, when many younger pilots of FBW transports now have no experience of hand-flying any jet at high altitude, even with a fully-functional EFCS ?
No, by definition it wouldn't apply to new/inexperienced pilots. I was more thinking about, and referring to industry experience with FBW/automation/protections today vice when the Airbus/FBW was introduced around thirty years ago. I don't know whether or not high altitude, high Mach Number, swept-wing flight aerodynamics is taught seriously to airline pilots today. As you know there is plenty of information for budding pilots that provide great information for keen pilots. Today, I''m not sure what "keen" means - it used to mean digging through everything that was available to one, without anyone suggesting it or requiring it.

That said, I believe that "FBW" and "Protections" are often conflated, and that the two subjects remain a point of disproportionate misunderstanding among many including Airbus pilots both experienced and new. I believe that some discussions particularly regarding the Airbus, suffer because of this.

Last edited by PJ2; 27th Feb 2017 at 18:58. Reason: mis-read the question!
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Old 27th Feb 2017, 19:13
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A Critique of Airbus
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Old 27th Feb 2017, 21:20
  #1395 (permalink)  
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The "Critique of Airbus" is nine years old. A more recent article (Flight International, Learmount), can be read at the link below by just signing in or creating a free account.

The technology is transparent to an atrophying of piloting/thinking/programming skills, which is largely a voluntary matter although individual airline automation policies may (and in my view, have), hinder(ed) the retaining of such skills. The success of the design and the incident/accident record are both now well beyond such arguments as represented by the "Critique...".

ANALYSIS: How A320 changed the world for commercial pilots

20 February, 2017, Flight International, David Learmount
As the world’s first digital fly-by-wire (FBW) airliner, Airbus Industrie’s A320 was positioned to bring commercial flying and flight management into the 21st century when it was rolled out in 1987.

The question at the time was: how was 21st century flying going to differ from the way it had been? The question now is: did Airbus get it right?

For Airbus, the A320 was more than just a FBW airliner. It was the still-young company’s debutante in the narrowbody marketplace. But above all – in the company’s strategic perspective – it was its first product in a planned family of FBW airliner types that would, as a result of their control technology, have very similar flying and control-system characteristics.

Nearly 10 years after the A320’s entry into service, by which time the type’s market acceptance was obvious, former Airbus president Roger Béteille admitted the decision to use FBW flight control was one of the most difficult he had ever made. He explained: “Perhaps we were too bold, but we had no choice. Either we were going to be first with new technologies or we could not expect to be in the market.

Cont'd at the link above

Last edited by PJ2; 27th Feb 2017 at 21:51.
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Old 27th Feb 2017, 21:56
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I have to throw in with 'bird, Chris, PJ, Wolf and others concerning flight dynamics and basic airmanship.

I do not understand the newguy questions - Confours or whatever the callsign is.

I question if the newbie has gone thru thousands of posts on this thread and seen the very lucid and accurate descriptions and discussions of aerodynamics, flight control laws, design philosophy, personal war stories.... and the beat goes on.

The 'bus control laws have been dissected over and again.

- When all the data was published it was obvious that the crew was not well-prepared and the most experienced aviator did not assert authority.

- The side stick position is not and was not visible to the "other guy".

- The jet has really great aero to get into a stall without obvious shaking, buffet, wing rock and so forth.

- The chimes and sounds and such did not direct the crew to a useful procedure or flight control input

- High altitude dynamics are lots different than down low. Not only is the TAS much higher, which makes even a slight control input result in fairly pronounced changes in pitch and roll, but the mach effects become apparent.

I hope this newbie will go back as far as possible and see all the outstanding discussion most of us here had, especially once all the recorders were made public.

I respectfully send....
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Old 28th Feb 2017, 03:16
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I'm just a lurker, but sometimes it's just hard sitting while "the party" gets hot again.
I'm trying to have a look, once again, from AF447 "pilot eye" and making abstraction of all knowledge about accident.
Imagine the scenario, well known, of that flight deck at the moment of the autopilot disconnection. The aircraft banked right rapidly and vario showed slight descent. "I have control!"; "D'accord!"(1)
Bonin moved the sidestick immediately, he applied the correction in lateral, but at "regular/normal" amplitude, as for an approach phase(2). Also, maybe he pulled unintentionally, as I and others presumed earlier here. We have to admit that in that short period of time, in seconds, all the important info, actions and communication were done. Both acknowledged the UAS. Robert read loud the ECAM messages: engine THR MOVE, Alternate law, meanwhile Bonin was absorbed in lateral control. Then Robert changed view from ECAM to vario, he noticed the huge climbing rate "ATTEND...", before he finished the sentence "Fais attention a ta vitesse!", the sidestick was pushed nose-down. The N1 was exceeding 100%.
Now, at 2h10m41s apparently Bonin was in control, he checked from his memory, UAS items: (THR) "yeah we’re in climb" then corrected the pitch to 5-7 deg, all seemed stabilized, but was only an apparent calm, before the disaster. Pilots had no physical cues whatsoever about the aircraft dramatic loss of speed and energy(3)
I read posts that zoom in BEA graphics, trying to show the novice hand flying, PIO, startle, panic etc.
I invite you to watch again the simulation, it happened much faster than this post reading up to here... watch the real deal, 40 seconds again and again, up to Stall at 2h10m52s (4).

https://www.youtube.com/watch?v=BR5kFOHVnUU

That fast they lost it.
(1) "No, I have control!"
(2)/(3) Training for flying at high altitude/Sidestick design, something to learn from little brother CSeries. The soft stops, pusher that "talks" to you about low energy, trim for speed, keep the pilot in the loop, see at 1:08

https://youtu.be/-Y2plnzdqPs?t=68

(4) next 20 seconds, stall + healthy positive vario?! I guess Bonin heard about "persistent false stall", BEA annexe 08. THR was mostly in excess of 100%, then TOGA, for 1 long minute before vario changed to descent. The noise and buffet of the fall, at 280 kmh(174mph). It was quite impressive, louder than a hurricane category 5 "I have the impression that we have some crazy speed"

"ERR, what are you doing?!" and stall warning miraculously went silent.
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Old 28th Feb 2017, 04:43
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Originally Posted by Concours77
Would you classify that thirty seconds as "jet upset"? If so, I would agree, and acknowledge that as the beginning of the Loss of Control? Especially so if the focus on Roll recovery cost airspeed and Pitch awareness? Where was FO Robert? Aside... Was Roll ever effectively managed? Captain remarked on it....
Concours, the word jet upset normally invokes an aircraft in a bad attitude such as the CRJ that crashed in Northern Sweden. This was a bit different. It was an oscillation that the PF was fighting and devoting excess attention to.

Most pilots have not experienced situations where their aircraft is acting contrary to their control inputs except perhaps situations which results from stalls. Those that have experienced this contrariness will remember the experience as very jarring and alarming. Although the AF447 roll oscillation was not particularly extreme nor rapid, it was contrary to Bonin's piloting intent, and he fought it vigorously and he was alarmed. At the same time, his trust in his control system was damaged.

Was AF447 ever stabilized? Yes, briefly in the 10 seconds before the stall. Afterwards it was again destabilized. Was Bonin in good control of himself, probably not. Why didn't Robert intervene? Perhaps because Bonin was assigned as PF by the Captain. Perhaps his personality was indecisive. Perhaps Robert's understanding of just what had happened to his aircraft's energy was lagging because of his own fear that Bonin had generated.

One thing is fairly certain in the period just before the stall. Panic within the AF447 aircrew was just below the surface. They had lost track of where the aircraft was within its flight envelope. They did not understand what had just happened to their aircraft to cause their difficulties.

From the Tognazzini blog on panic comes this little jewel:
3. Panic Desensitization A third approach to reducing or eliminating panic is through desensitization. You don’t hear a lot about it, because we don’t do much panic desensitization. Instead, we do nice, safe simulations that we think work as a substitute. They don’t.
Looking back at my own training to land jets aboard ships, I find that it was all extremely challenging and almost every flight during training took you out of your comfort zone. One effect of this training was to desensitize you to hazards. You knew that the hazards were there but you knew you could handle them.

Perhaps we should deliberately throw panic inducing exercises at aircrews in the simulator to create some of this d
esensitization?
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Old 28th Feb 2017, 13:26
  #1399 (permalink)  
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Learmount's Take

ANALYSIS: How A320 changed the world for commercial pilots

20 FEBRUARY, 2017 SOURCE: FLIGHT INTERNATIONAL BY: DAVID LEARMOUNT LONDON
As the world’s first digital fly-by-wire (FBW) airliner, Airbus Industrie’s A320 was positioned to bring commercial flying and flight management into the 21st century when it was rolled out in 1987.

The question at the time was: how was 21st century flying going to differ from the way it had been? The question now is: did Airbus get it right?

For Airbus, the A320 was more than just a FBW airliner. It was the still-young company’s debutante in the narrowbody marketplace. But above all – in the company’s strategic perspective – it was its first product in a planned family of FBW airliner types that would, as a result of their control technology, have very similar flying and control-system characteristics.

Nearly 10 years after the A320’s entry into service, by which time the type’s market acceptance was obvious, former Airbus president Roger Béteille admitted the decision to use FBW flight control was one of the most difficult he had ever made. He explained: “Perhaps we were too bold, but we had no choice. Either we were going to be first with new technologies or we could not expect to be in the market."

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Livery styles may have changed since 1987, but much of the original aircraft christened by UK royalty lives on
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From the pilot’s point of view, the fundamental change in the A320 was the addition of flight envelope protection (FEP), which all aviators hope – and most would like to believe – they will never need.

The most visible difference was the replacement of a control yoke with a sidestick. The stick has a relaxed central position such that, when released to it during manual flying, no roll or pitch input is demanded of the pilot.

Control inputs to the sidestick and to the power levers in manual flight are intuitive, even to pilots trained on a mechanically controlled aircraft, but initially it feels strange not to have to follow up a manually commanded pitch change with trim inputs. There are no trim switches, and the conventionally positioned pitch trim wheels on the centre console are not used in flight except as an emergency back-up pitch control system. Pitch change demanded manually via the sidestick is delivered by the elevators, and the act of centring the sidestick commands the stabilisers to trim to the selected flight profile.

In 1997, one of Flight International’s test pilots, Peter Henley, benefiting psychologically from the knowledge that the A320 series had been in successful service for nearly a decade, flight-tested the new A319. He had this to say about flying the aircraft manually: “The sidestick works in the conventional sense and produces a rate of aircraft response which feels right to a pilot accustomed to a conventional aircraft. A comforting feature of the system is that the apparent response to the control and the feel remain constant throughout the flight envelope.”

FEP as a concept was difficult, at first, for flightcrew to get their heads around. In the A320 (and all subsequent FBW Airbuses) it works like this: with its flight control computers selected to normal law, the pilot’s manual inputs, when the aircraft is flying within the flight envelope, are transmitted direct to the control surface actuators unaltered by the computers, so pilots get what they are asking for.

If, however, the pilot allows the aircraft to get close to the edges of the flight envelope, warnings are triggered. If it continues right to the edges, the aircraft will be prevented from stalling, overbanking, overspeeding or overstressing, no matter what the pilot input – or the lack of pilot input, if that happens to be the problem. The FEP also provides an automatic reaction to the effects of windshear.

Meanwhile Airbus’s long term plan – completely visible in the fleet today – is that all FBW Airbuses (that is all Airbus types except the A300 and A310 series) would have so much commonality in terms of human/machine interface and systems control philosophy that for a pilot trained on one of the types, cross-type qualification on the others would be achievable with minimal training time and cost, even across the widebody/narrowbody divide.

FBW as a technology was not a new idea in the early 1980s when the A320 was in gestation. The military had used it extensively, and Airbus’s Toulouse forebear Sud Aviation (later Aérospatiale) had installed analogue computer-driven FBW in Concorde, its supersonic joint venture with British Aircraft Corporation.

To put the Airbus FBW venture into the context of its era, only one other airliner manufacturer was actively considering FBW control. In the mid-1980s, Boeing had proposed a FBW-controlled narrowbody designated the 7J7. It was to be fitted with twin aft-fuselage-mounted unducted fan engines (“propfans”), and intended for service entry in 1992. However, problems with the propulsion technology ultimately defeated the manufacturers, and a propfan has still not been successfully developed.

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Popularity of the A320 has been the payoff of an existential choice: be first with new technology or, likely, be out of the market
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Boeing introduced FBW seven years after the A320’s service entry in its hugely successful 777 widebody, but the company’s direct narrowbody competitor for the A320, the perennially successful 737 series, is still selling well despite having conventional mechanical controls. The 737’s flight deck is just as highly automated as the A320’s in terms of its autopilot/autothrust and flight management system capabilities, but it does not have active flight envelope protection, just warnings and a stickshaker.

The question 30 years after the A320 series’ service entry is: did Airbus get it right? The market says yes, and so do the accident statistics (or lack of them). But have the original flight laws/software that defined the A320’s flying characteristics at service entry in 1988 had to be changed in the light of experience? Soon after entry into service the manufacturer added a low-energy warning to the system, but otherwise the simple answer seems to be no.

Certainly no fundamental changes have been needed, but there have been a few adjustments to take account of higher gross weight or aerodynamically modified versions – like engine nacelle changes. Airbus also admits blandly: “A rotation law has been implemented for better take-off performances. The crosswind landing is made easier thanks to a new decrab law.”

The cockpit in the latest versions looks remarkably similar to the original, but its capabilities have been updated like those of other airliner types over the past 30 years. These updates take account of the drift away from navigating by radio beacons toward global navigation satellite systems. For example, they include precision area navigation, required navigation performance, vertical navigation, autopilot-flown traffic alert and collision-avoidance manoeuvres, runway overrun warning and prevention systems, and electronic flightbags. The company says there have been no changes to its A320neo cockpit.

So, despite all the initial apprehension about the A320’s FBW/FEP systems, they have proved themselves to be remarkably durable.

Cockpit automation

Airbus Industrie’s ambition to design a flight control system that would help pilots do their job better and more safely than purely mechanically connected controls drove it, in the early 1980s, to conduct a fresh examination of how pilots’ roles were changing in the modern commercial aviation environment. The company concluded that pilots would definitely remain essential, that the cockpit design would reflect their primacy as decision-makers, but that also they would need more back-up in the age of highly automated cockpits, busier skies and an expectation of zero accident risk.

The new cockpit automation philosophy first launched in the A320-series anticipated an imminent era when pilots would hardly ever trip the autopilot out, and aircraft could rely largely on flight management systems for navigation, because their computational capabilities, speed and accuracy far exceeded the mental capacity of pilots. These things are taken for granted now, but then they were unfamiliar.

Autopilots combined with autothrottle had long been a useful pilot tool, but they work equally well with FBW or the old mechanical control systems. The latest variant of the venerable 737-series is a good case in point, and it still competes commercially with the A320 series.

There are times, however, when the autopilot – only capable of operating when the aircraft is within its flight envelope – is designed to trip out if it approaches the limits of its operating capability for whatever reason. This is the point where the pilots are expected to take over, using their flexibility, ingenuity and training to take charge of a situation that might be surprising, complex and confusing.

At this point, a glance at 1970s/1980s military control technology can aid understanding of the philosophy behind the extension of FBW capability to encompass FEP. In the 1980s there was direct cross-fertilisation of ideas between the computer-controlled dynamic (CCD) system of the Dassault Mirage 2000 fighter and the Airbus team, some of whom had flown it or military types like it.

CCD, which would now be called FBW with FEP embedded in the software, enabled a combat pilot bent on obtaining maximum performance from the aircraft to be able to demand it at any speed by moving the joystick and throttle on to the stops with no fear of overstress or damage. This liberated the pilot to concentrate on mission tactics, and enabled the airframe to be designed with “relaxed stability” without fear of loss of control, making the aircraft much more manoeuvrable.

FEP keeps the aircraft operating within safe parameters even if the pilot mishandles or neglects to control it, and the full authority digital engine control system does the same for the powerplants.

Airbus’s ultimate reason for moving into digital FBW was that it was now a sufficiently mature technology for use in the commercial arena, and the safety benefits of FEP were so obvious that it simply did not make sense not to use it.

Testing the prototype

In 1984, when Airbus Industrie was flight-testing its FBW system – some three years before the first A320 was rolled out – the manufacturer’s then senior vice-president for engineering, Bernard Ziegler, invited Flight International’s air transport editor David Learmount to take the controls of the FBW testbed A300B2. The aircraft carried the FBW flight computers linked to a single sidestick control that was mounted at the left-hand seat. The right-hand seat pilot had a conventional yoke with mechanical control runs.

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Airbus named its A350 assembly line after A320 champion Roger Béteille, speaking
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In a short pre-flight briefing, Ziegler explained that, although the aircraft might feel as if it was acting in response to a direct connection between the sidestick and the elevators and ailerons, the relationship was more subtle. The spring-loaded sidestick, when relaxed to its central position, commanded – via the flight control computers – a 1g flight profile and a zero roll rate. When displaced in pitch the stick commanded a proportionate change in the vertical acceleration by operating the elevators, but the computers would limit the positive or negative acceleration to the maximum allowable g load if the stick was pushed or pulled on to its stops.

Ziegler explained that sideways stick displacement commanded a proportionate roll rate up to a maximum of 15°/s. And, he added, the system would not let the pilot stall the aircraft. He told his ingénue co-pilot he could try it when airborne.

In the testbed A300, the sidestick’s signals were sent to the computers which, in turn, sent signals that activated control surface servos according to the stick displacement and the flight laws embedded in the system software.

The purpose of this flight was to demonstrate the system’s FEP in action. Learmount took over the sidestick seat when the aircraft was at a safe altitude, Ziegler gave him control and invited him to try to stall the aircraft in clean configuration. The throttles were set to idle, and Learmount chose to let the aircraft slow down in level flight. When the indicated airspeed was approaching the stall at about 100kt (185km/h) the nose began to dip to maintain an angle of attack just above the stall. Learmount pulled the stick back to raise the nose and induce a stall, but the nose continued to dip and the airspeed continued – marginally – to reduce until it reached what Ziegler later explained was “alpha-floor”. This is the stalling angle of attack. At that point, with the stick still fully back on the stops, the engines wound up automatically to take-off/go-around power. As the airspeed increased and the angle of attack was just clear of the stall, the nose began to rise steadily and the aircraft powered upwards out of its brief descent.

The FEP limits the angle of bank more simply: a pilot roll input on the stick simply stops being effective at a maximum of 67° bank. Overspeed protection is provided by raising the nose to keep the speed within flight envelope limits, even if there is nose-down pilot input.

Pilot mental appreciation of how the FBW laws work in practice seems to be just a matter of familiarity. Manual flying in the A320 series feels perfectly intuitive, so it should not matter whether the pilot thinks of a pitch-up displacement of the sidestick as a demand for a proportionate elevator deflection, or as a demand for a proportionate increase in vertical g (which is how the FBW system delivers it), because the effect is identical: the nose-up attitude increases as demanded by the pilot. Likewise, it should not matter whether a pilot displacing the sidestick to the left is demanding a proportionate aileron deflection or a proportionate rate of roll, as the effect is identical.

Having experience not only of developing Airbus’s cockpit automation philosophy but of introducing conventionally trained line pilots to it in the early days, experimental test pilot Etienne Tarnowski remembers how it felt persuading them that the A320 was not taking control away from the pilots and giving it to a computer.

Tarnowski says it was useful to provide them with analogies they were familiar with. Pilots do not complain that yaw dampers or turn co-ordination systems take control away from them, he suggests, but rather see them as assistants. FEP in pitch loading does not take control away from pilots hit by a storm downburst on final approach, but liberates them to pull fully back on the stick knowing it will provide absolute maximum aircraft climb performance without fear of stalling.

Most questions from trainees, says Tarnowski, were not about manual flying or the flight controls, but about getting the most from the flight management guidance computer via the autopilot, autothrust and flight management system: managing the automated systems and choosing the best autopilot modes for any particular phase of flight. This happens to be the same in highly automated cockpits that do not work with FBW/FEP.

Tarnowski believes there would have been an early days benefit for new A320 crews if Airbus had merged its design and training teams earlier in the design process, but says: “I am not convinced that an earlier merging of the test and training communities would have changed the design of the A320.” It would probably have helped the instructors, however.
Winnerhofer is offline  
Old 28th Feb 2017, 13:46
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Winnerhofer: the last paragraph is about the only comment worth noting, at this point. I find it interesting that Learmount wrote about himself in the third person. (Well, that's how your Cut and Pasted article presents it ...)
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