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