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TAM A320 crash at Congonhas, Brazil

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TAM A320 crash at Congonhas, Brazil

Old 5th Aug 2007, 14:04
  #1161 (permalink)  
 
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Tyro Picard
What you have said is absolutely correct regarding the TLA sensors.
However, before a certain 'mod', if you had a failure or disagreement of one of the sensors in flight then the Approach Procedure read like this:
  • IF AUTOLAND NOT USED
  • At 500ft AGL:
-ENG MASTER (affected).......OFF
Affected engine must be shut down, because when thrust levers are retarded, A/THR would remain in SPEED mode. During flare the thrust of the affected engine would increase to maintain the A/THR' target speed.

This actually happened to a colleague of mine some time ago and definately got our attention. One assumes that the 'mod' had been done on this aircraft? I don't know if there is any relevance here, but you never know.
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Old 5th Aug 2007, 14:12
  #1162 (permalink)  
 
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to not think that machines may not work properly, or with the highest regard of human life is to forget the lessons of HAL 9000.

(younger posters please view "2001")

can we safely say that the airbus is not an extension of the pilot?

I am also reminded of the opening credits to the TV show "The Jetsons"...George screams to his wife, jane, STOP THIS CRAZY THING.

both deal with futuristic automation.

now some may not see the connection, some may even ban me from the thread, but we have a situation in which 2 veteran pilots couldn't make a plane they had been flying all day, stop at an airport they were very familiar with.
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Old 5th Aug 2007, 14:37
  #1163 (permalink)  
 
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bomarc's got it - and at this point in what we know of the investigation, the only surprise to me (forgive the gallows humor) is that the CVR didn't capture the words "What's it doing now???"
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Old 5th Aug 2007, 14:42
  #1164 (permalink)  
 
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Originally Posted by TyroPicard
Both (known) TLA failure modes produce thrust Idle on the ground, and we have heard that 1.2 EPR was recorded on No.2 engine. Obviously some deep technical investigation required.
TP
These two failure modes are "Thrust Lever Disagree" and "Thrust Lever Fault".

Thrust above idle is set only if:

TL DISAGREE (different TLA readings from the two sensors):
- FLX or TOGA was set during takeoff: FLX or TOGA is retained until thrust reduction altitude
- MCT or below in flight with slats retracted: value of higher TLA sensor is used, thrust limited to MCT.

TL FAULT (no valid TLA reading):
- FLX or TOGA set durng takeoff: FLX or TOGA is retained until slat retraction, at slat retraction: MCT
- MCT or below in flight with slats retracted: MCT

In all other cases, the FADEC selects IDLE thrust!

Specifically:
- always on the ground (except during take-off)
- always with slats extended (except during take-off)

So we can pretty much rule out a thrust lever sensor failure of either kind here, especially since its ECAM message would have been accompanied by an aural signal, which is not on the CVR transcript.
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Old 5th Aug 2007, 15:39
  #1165 (permalink)  
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We have some experienced AB heads here - do any of you have any inkling of what is causing this apparent 'mind-set'? Is it that the A/T system, as TP says, WILL reduce the thrust in an Autoland and BECAUSE A/T apparently remains engaged on a manual landing there is some 'vestigial' brain function that says I do not need to? In both cases there is no visible difference on the throttle quadrant. Would the answer be to teach A/T disconnect in the flare on a manual landing thereby reinforcing the 'pilot' inputs? Something needs to be done, and I don't think issuing a reminder to pilots to close the levers will crack the inbuilt block.
Picking up on TP's answer, somewhere back in the thread there was a mention of 1.2EPR on the No2 (Nod's post #1113?). IF this is pukka, is that what you would expect from the A/T as it tries to maintain Vapp with No2 thrust? It seems quite low to me. Is it possible that a partial throttle back from CLB had taken place and would the EPR then be lower? by BOAC
As far as I'm concerned, there is no block (maybe I'm wrong), crews that are trained to do autolands are aware that thrust is automatically retarded as a matter of system training, this function (in my experience) is not used at all with LVP procedures, main reason being, we always use REV, and it can't be used if we leave thrust levers in CLB.
.
Not too sure about this 1.2 EPR, I would assume something in the range of 1.4 for CLIMB power .
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Old 5th Aug 2007, 15:42
  #1166 (permalink)  
 
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Che guevara,

For the MBK MSN, that failure is not valid (the FCOM for that MSN has a different procedure...for a TL fault, idle is selected on the affected engine when slats out). I also thought about that failure, but a friend of mine corrected me...
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Old 5th Aug 2007, 15:52
  #1167 (permalink)  
 
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Thank you Rippa
I was just wondering what the MSN and mod status was on this aircraft, and I think you answered that for me.

Chao
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Old 5th Aug 2007, 16:38
  #1168 (permalink)  
 
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I wish to disagree with Sarah737 that the chain of events started at 20 feet. That may be the case in the event of a "slip" failure in only grabbing a single one of the pair of Thrust Levers, if the pilot flying's intention was to move both to Idle. In the event of a rule based or knowledge based mistake, you have to go much further back into design philosophy, pilot knowledge-training-experience, procedures, checklists, briefings etc.

ICAO Annex 14 2.9.5 requires the aerodrome to publish a NOTAM or inform the pilots via AIP AD2 or ATC that the runway is "slippery when wet". The braking friction testing carried out by the airport operator did not show this characteristic under test conditions. There were no braking action tests reported as being carried out prior to the TAM landing accident.

Attachment A7 gives further details of slippery when wet.

Annex 15 Appendix 1 in the listing of AIP contents, shows that AD 1.1 sub-para 5 is the place where the State is required to publish "
friction measuring device used and the runway friction level below which the State will declare the runway to be slippery when wet;".

Does anybody have a copy of AD 1.1 for Brazil to see what values are published by the State?

As for PJ2's comments in relation to touchdown point, you can work it out fairly accurately if you have enough engineering skill and know enough about how the data were collected.

If the earlier reports of 11 seconds to brake application are correct, then this would indicate a distance of approximately 1000 metres down the runway. This gave approximately 10 seconds on the runway and then the 4.5 seconds off the runway prior to going through the taxiway retaining wall.

Is anybody going to do the 1.20 EPR calculation to work out the forward thrust contribution and compare it with the expected "ground" idle?
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Old 5th Aug 2007, 17:40
  #1169 (permalink)  
 
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Is it true that compliance with a service bulletin is mandatory if it arises from an accident "cause" and not from an accident identified "risk" ?

NO


did I hear a light switch click
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Old 5th Aug 2007, 19:01
  #1170 (permalink)  
 
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BOAC

Picking up on TP's answer, somewhere back in the thread there was a mention of 1.2EPR on the No2 (Nod's post #1113?). IF this is pukka, is that what you would expect from the A/T as it tries to maintain Vapp with No2 thrust? It seems quite low to me. Is it possible that a partial throttle back from CLB had taken place and would the EPR then be lower?
The thrust on #2 has been reported as both 1.02 and 1.2 EPR. Either could be possible given what we know of the pilot's intended landing technique of flying 1 dot low. Moving to this approach angle earlier would have resulted in a flatter approach, probably a longer distance to touchdown and a higher approach thrust, perhaps 1.2 EPR. An increased vertical rate later in the approach to go below the slope and meet an earlier planned touchdown point would yield the reverse, with thrust reducing to near idle values making 1.02 EPR possible. Either way, if the reporting of the AIT is correct the thrust on #2 remained at the same level as it was at the moment the autothrust disconnected due to reverser activation on engine #1. My suspicion is that the first case is the more probable but only facts and analysis published by the investigators will make that clear.

One thing to consider is that you may be reading too much into these very few occurrences relating to operations with a deactivated reverser. Accidents are generally so rare that the jump from observing the specific mistake that may have been made by this crew (if that is the case) to the general conclusion that there is a fault in the overall system or procedure design is not statistically valid.

We know of 3 or perhaps 4 cases where something like this has occurred in almost 20 years of aircraft operation among the Airbus FBW fleet. We do not know how this compares to the number of over-runs or loss of control events on runways related to thrust manipulation with a reverser deactivated that have occurred to non-Airbus FBW aircraft during the same time period or number of cycles. Many such instances for both the Airbus or other aircraft will never become widely known simply because the reporting of them will never make it to publicly scrutinized databases such as the ones people here are using to form their conclusions.

Unless or until we have those statistical answers we don't know whether the cause of the events on record is best ascribed to system design, operator procedure, pilot training or individual error, and we also don't know whether their occurrence is more prevalent on Airbus FBW aircraft versus transport category aircraft in general. The best improvements to the overall level of performance of the system requires that analysis, though attempts to improve each element can and should take place as result of the facts elicited from every event.

A good example of this is the FWC modification that followed the TransAsia accident. The manufacturer did respond to the inquiry's finding and provided a discrete warning to address the mismatched thrust lever situation. And, it seems to me that the fix: "Eng X Thrust Lever Above Idle" accompanied by a Continuous Repetitive Chime (CRC) is more inherently logical to the situation than continuing the "Retard" callout.

This is true for several reasons, the first being that to get into the situation the pilot most likely has to have already retarded only one of the thrust levers despite the earlier callout(s). He may be filtering the “Retard” callout because he believes he has already responded to it. A new and different warning will be more likely to draw his attention to the fact that the current thrust lever configuration is not normal and probably not what he intended as opposed to repeating the “Retard” callout for a third, fourth or fifth time.

Secondly there's the return to the ambiguity of the pilot's intentions. The call "Retard" is effectively a command intended to complete a landing. Now that one thrust lever is at idle and one is in climb, is that still the pilot's intention? If not then the "Retard" callout is now contrary to the pilot's changed intention and could add to, instead of resolving, the confusion.

Thirdly, the presence of a visual as well as an aural warning ensures that the PM (pilot monitoring) is more effectively drawn into the loop regarding the position of the thrust levers. He is already monitoring the ECAM at this point so a warning that is explicit and is displayed right in front of his eyes is likely to be understood. In most instances that might occur the thrust levers will not be in the position the PF believes them to be, but he will believe that they are correctly placed. The PM not having moved the lever(s) himself is less likely to have a preconceived false belief of their position. Producing a warning that he can understand immediately is probably the fastest way to change the overall crew understanding of the position of the levers, as opposed to continuing a callout that's been heard at least once or twice already and is a routine part of every normal landing.

Having said all of this, it is a very fair question to ask why this modification to the FWC was not considered mandatory as opposed to optional. Both Airbus and the various regulatory agencies that certify the aircraft will have to provide an answer for that, as will TAM when it comes to why they chose not to install an available modification that may have been critical to the safe resolution of this accident. My guess is that the answer will lie in the statistics and that the regulators will say that the probability of occurrence of the failure scenario was too low to make installation of the warning mandatory from a certification perspective. Unfortunately, a very low probability is not the same as no probability and this instance may be the one that falls into that gap. That is a sad fact that will comfort nobody, but it is a possibility that occurs in the certification of aircraft and just about every other product which has a human safety component to it.

ELAC
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Old 5th Aug 2007, 19:09
  #1171 (permalink)  
 
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FROM : AIRBUS FLIGHT SAFETY DEPARTMENT TOULOUSE
ACCIDENT INFORMATION TELEX - ACCIDENT INFORMATION TELEX
The data which follow have been approved for release by the Brazilian investigation
authorities.
It is confirmed that the aircraft was dispatched with the Engine 2 thrust reverser inoperative
as authorized by the MEL.
It is confirmed that the associated operational procedure of TAM MEL was updated
according to current MMEL page 02-78 p1 SEQ 001 REV 29 which reminds the crew to
select both thrust levers to idle before touchdown and requires to select both reversers at
touchdown.
The following is the sequence of events according to the recorders:
Final Approach phase
· The aircraft was approaching runway 35L.
· The last wind information given to the crew by the ATC was 330°/8kts.
· The runway condition given to the crew by the ATC was wet and slippery.
· Landing configuration was established with Slats/Flaps fully extended, gear down,
ground spoilers armed, autobrake selected to MED.
· Approach speed was 145 kts
· The final approach was performed with Autopilot OFF - disconnected at about 370
feet (radio-altitude), Flight Directors ON, Auto-Thrust (ATHR) ON.
· The CM1 was the Pilot Flying.
· The crew approach briefing included a reminder that only the left engine thrust
reverser was available.

Flare and touch-down
· During the flare, the "RETARD" call-out has been normally triggered
· The "RETARD" call-out has been triggered 3 times, ending at the selection of the
engine 1 reverser.
· Before touchdown, the engine 1 throttle was retarded to idle.
· The engine 2 throttle is recorded in the Climb position and remained in this position to
the end of recording.
· Preliminary trajectory computation indicates that the aircraft landed in the touch-down
zone.
Landing roll
· Just after touch-down, idle reverse was selected on engine 1, followed within 2
seconds by the selection of max reverse which was kept to the end of recording.
· Following reverser 1 selection, the ATHR disconnected as per design and remained
disconnected to the end of recording.
· With the engine 2 throttle being in the Climb position: 1/ the engine 2 EPR remained
at a value of approximately 1.2 corresponding to the EPR at the time of ATHR
disconnection; and 2/ the ground spoilers did not deploy and the autobrake was not
activated.
· Maximum manual braking actions began 11 seconds after touch-down.
· Rudder inputs and differential braking have been applied during the landing roll.
· The aircraft overran the runway at approximately 100 kts.
DFDR and CVR data show no evidence of aircraft malfunction.
At this stage of the investigation, and as already indicated in the previous AIT n°3,
Airbus remind all operators to strictly comply with the following procedures:
A- During the flare at thrust reduction select ALL thrust levers to IDLE.
B- For the use of the thrust reversers when landing with one Engine Reverser inhibited
refer to :
· For A318/A319/A320/A321 MMEL 02-78 Page 1 Rev 29
· For A310 MMEL 02-78 Page 1 Rev 17
· For A300-600 MMEL 02-78 Page 1 Rev 15
· For A330 MMEL 02-78 Page 1 Rev 17
· For A340 200/300/500/600 MMEL 02-78 Page 1 Rev 19
I think it wasn't posted before.
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Old 5th Aug 2007, 19:22
  #1172 (permalink)  
 
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ELAC, thank you very much for your mildly expressed, yet very precise thoughts. A nice variety to some others.
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Old 5th Aug 2007, 20:43
  #1173 (permalink)  
 
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Radalt

In relation to the Airbus information release, please remember not to correlate 370 feet radalt with 370 feet above touchdown zone elevation.

The pictures of the aircraft undercarriage show three brakes ON and one brake OFF when pulled from the accident site. Do not imply that the fourth brake had failed, as there was damage to that leg on impact. Do not make any assumptions relating to brake wear indicators.

Regards

Our Man
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Old 5th Aug 2007, 21:28
  #1174 (permalink)  
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Originally Posted by ELAC
One thing to consider is that you may be reading too much
I accept your points, but we apparently have here a totally illogical action which IMO separates this from all other 'events'. NB I do not necessarily suggest
there is a fault in the overall system or procedure design
although I do feel the non-moving throttles contribute hugely to the confusion which obviously has existed in several instances.

I also find it strange that no-one comments (in the CVR I have seen) about what must have been a more difficult touchdown than usual due to the asymmetric yaw and probable float with the increased power on No2.
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Old 5th Aug 2007, 21:33
  #1175 (permalink)  
 
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from the times wire service (LA times)

"Maia said aircraft equipment failure had not been ruled out, and that it was possible the pilots had shifted the throttle lever correctly but that the plane's computer had failed to respond."

For a moment, let us give the benefit of the doubt to the men and not the machine.

we must have options for this scenario.

I believe my little checklist would have prevented some if not all deaths in this case and that all pilots must have in their little bag of tricks all sorts of options.
bomarc,

My comment was based on the reported content of the Airbus AIT by Hand Solo in post #1070, the content of which is now confirmed with TripleBravo's posting of the latest AIT. The exact report turns out to be "The engine 2 throttle is recorded in the Climb position and remained in this position to the end of recording."

Based on this, there is perhaps a remote possibility of the failure being something other than the thrust lever accidentally being left in the climb detent, but the probability that the thrust lever was left in the climb detent is very, very high. I don't have current access to an A320 FCOM but the alternative scenario would require something like the simultaneous failure of both TLA sensors and both channels of the engine's FADEC or both of the SFCC's (Slat/Flap Control Computers). Still, that's a probability, not a certainty. Hopefully the investigation will answer this question for us.

On a general level, and leaving aside the physical obstruction case (which there is no supporting evidence of as yet in this instance) there's an awful lot of concurrent failures that would have to happen before the procedure you described would become the necessary set of steps to save the situation. In practice it would likely be about a 99% probability that the symptoms: No Effective Deceleration, No Ground Spoiler and No Autobrake would come about because 1 thrust lever has not been retarded to idle. So, the best training in my opinion would be:

1-Treat the most severe symptom first - establish maximum braking and reverse to stop the aircraft, as per Airbus' current memory item.

2-Confirm the most likely source of the problem - are both TL's at Idle (again as per the current memory item)? If not - Max available reverse on both engines.

Creating a more complex checklist such as the one you suggest:

Maintain directional control with rudder pedals

flaps-config 3

manually select speedbrakes extend

maximum manual toe brakes

both engines, fuel cutoff levers/switches-CUTOFF
to cater to the <1% case would probably create more problems than it solves.

For example, in the procedure as you proposed it, applying the brakes comes 4th in order of priority where in practice I would suggest that establishing the most effective and certain means of deceleration has to be the first priority 100% of the time unless an immediate decision to reject the landing is made. If we were to tell a pilot to memorize this and carry it out any time there is a lack of effective deceleration, what are the chances that the distraction of attempting to move the flap lever and then extend the speedbrake will delay or prevent the pilot from applying maximum manual braking? Will the PF do it or will he command the PM to do it? If so, time lag. If the PF does it, how will that work if the PF is the F/O? If only the Capt. does it will he also take control of the aircraft? If not will his actions distract the F/O from maximum braking? Will any or all of these questions increase the number of times that a aircraft is not stopped successfully for a lack of deceleration event versus the current procedure?

For a moment, let us give the benefit of the doubt to the men and not the machine.
When analyzing accidents no one, man or machine should be provided with "the benefit of the doubt" where there is any chance of discerning the the facts and the reasons for why things happened. All of us posters on PPRuNe are just hypothesizing based on the limited information available to us, and most certainly my thoughts are not to "convict" the pilots of the "crime" any more than I think that there is merit in the ongoing attempts here to hang the accident on the Airbus' non-moving thrust lever system.

My comments are simply my thoughts as to what I think the critical issues to examine should be based on the information introduced by the authorities so far. If I've phrased any of them as being conclusions as opposed to observations contingent on the facts stated being true, well, I've written it wrong. Whether the actions of the crew or the aircraft were appropriate or reasonable for the exact circumstances they found themselves in is a judgment matter for the investigators to decide and certainly beyond me based on what is known up to now.

Regards,

ELAC
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Old 5th Aug 2007, 21:49
  #1176 (permalink)  
 
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my dear elac:

consider...if one were to first hit the toe brakes, one would disconnect the autobrakes...so

maintain directional control...you probably are doing that anyway

flaps config 3...now you get to

put out the speedbrakes

and hopefully the plane will more fully settle to earth, triggering the autobrakes

which would be a good thing

shutting down the engines is the magic button requested earlier if for some reason other than pilot error, the engines have run away.


now the engines are dead, but the hydraulics were there to bring the flaps to config 3 and extend the speedbrakes

and hopefully the plane still has accumulators for the wheel brakes.


that is my thinking...
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Old 5th Aug 2007, 22:21
  #1177 (permalink)  
 
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put out the speedbrakes
and hopefully the plane will more fully settle to earth, triggering the autobrakes
Sorry bomarc - it's the signal to extend Ground Spoilers that activates the Autobrake. To pull the speedbrake lever back you push it down first - this disarms the ground spoilers. With your memory drill - no Autobrake.
if one were to first hit the toe brakes, one would disconnect the autobrakes
True, and thus get more brake pressure which is just what you want.

if, to land an airbus,one must always retard the throttles at a given radio altitude...what happens when you need to carry power to the runway...with a huge wind for example
Not a fixed RA - you close the thrust levers when you think you should, perhaps early or late depending on how the last bit of your approach worked out. The Retard call is a reminder which is only heard if the T/L are not at Idle. And with a huge headwind the A/THR will do the speed management for you - but that's way off topic.
TP

Last edited by TyroPicard; 5th Aug 2007 at 22:33. Reason: Added the last quote and response.
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Old 5th Aug 2007, 22:43
  #1178 (permalink)  

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With all this computer based logic that will not let the pilot take certain actions with the engine/flight controls, can anyone describe the scenario where he would (should be allowed to) purposefully select climb power on one engine while full reverse is selected on the other engine and the aircraft is on the ground, decelerating with manual braking being applied? If not, what is the logic that would allow this condition to exist while inhibiting other functions such as GS and auto brake?
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Old 5th Aug 2007, 23:06
  #1179 (permalink)  
 
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...or the logic of a Retard warning that ceases even though one TL is still in CLB.

Why wasn't this AD'd after Taipei?
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Old 5th Aug 2007, 23:10
  #1180 (permalink)  
 
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A310driver - forgive me if I am wrong but you appear to suggest that Airbus should have 'idiot proofed' their design. It's rather difficult to do that, and just as it is postulated that a million monkeys with typewriters, given infiinite time, will type the works of Shakespeare, so will a large number of pilots, given sufficient time, find a hole in any system design. Personally I am still wondering why on earth they could land with one engined in rev idle and the other in the climb gate. It so utterly defies logic to anyone who understands the 'bus that in could only be considered an unintentional error. As an aside it is perfectly feasible to land a 744 with three engines in idle and and one thrust lever advanced. How that affects the reverse/autobrake situation I haven't had time to investigate.
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