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Old 27th Jul 2007, 01:27
  #562 (permalink)  
Join Date: Mar 2003
Location: BC
Age: 72
Posts: 2,452

1 - If the A320 touches down with the autothrust engaged (I suppose it is the most usual), is it mandatory to put or keep BOTH levers exactly in IDLE detent or BOTH levers in reverse (if reverse thrust is deployed) in order to desengage the autothrust ?
First, it is not "usual" to touchdown with autothrust engaged. The thrust levers are both to be pulled back to "IDLE" (zero degrees thrust lever angle) by 20ft on a manual landing and by 10ft on an autoland.

The AOM does not specifically state that "both" thrust levers are to be pulled back to IDLE because there is no conceivable reason on Airbus or any aircraft I have ever flown not to close the throttles completely when landing.

I hastily add that this is not a comment on potential and actual errors made by crews - that is a human-factors issue however, and not an operational issue. That said, the AOM does specify the plural, "Thrust Levers" in all documentation in all normal and abnormal Airbus AOM SOPs I have read.

2 - If the plane touches down with autothrust engaged and soon after BOTH levers are put in reverse, what happens to the engine with the faulty reverse ? Will any alarm sound ? Will the AutoThrust keep engaged in order to reduce thrust in this engine with a faulty reverse ?
As per documentation in our AOM, the engine with the locked out reverse will increase it's idle RPM slightly and thereby increase forward thrust slightly.

No, no alarm will sound. There is no need. Operating with a reverser locked out is in the realm of "normal" operations with some operational considerations written and , while not written, experienced airmanship brought to bear. A u/s thrust reverser is not an abnormality in the same sense that jammed slats/flaps etc are. A u/s reverser in and of itself is no reason to stop operations or divert. That said, there are a host of reasons which may (and should) influence that initial position.

The autothrust will not keep engaged. It is disengaged (and cannot be re-engaged through thrust lever position alone) when the thrust levers are pulled back to IDLE. In fact, they disengage slightly above 0-degrees TLA but that is technically academic point at this stage.

3 - If, however, the plane touches down with autothrust engaged and soon after ONLY ONE of the levers is put in reverse and the other is kept at, let's say, only 2 degrees over idle position (without the "donut" pointing neither idle nor Max Climb position), will the AutoThrust simply desengage or put the left engine at Max Climb power ? And as I understood about the A320 Thrust system, would the lever even so keep steady at those 2 degress above the idle "donut", making it difficult to the pilot to realize that the engine was at full forward thrust ?
To be a bit fussy, I'm not sure of the exact TLA at which the autothrust disengages but I believe it to be slightly above zero degrees TLA.

However, I know what you are driving at and my response to the question is, the TLA position "restricts" the amount of available thrust level to the thrust lever position. I cannot imagine a design which, in some fashion, would "see" a partially-open thrust lever, and, without crew input, "decide" to increase to TOGA thrust on its own without the thrust lever so moving to permit this - such a serious design flaw would and should be immediately seen by engineers long before the airplane made it into production.

If for whatever reason, (human factors, rapidly unfolding/deteriorating circumstances, environmental factors such as turbulence, darkness, unfamiliar operating circumstances, surprise, etc), a thrust lever remained in a position which would permit the engine to increase power, it will do so. There is a note in the AOM in the Start section that warns the crews to ensure that the thrust levers are at the IDLE position before start because they will accelerate to the rpm/thrust setting permitted by the position of the thrust levers. The item is in the Before Start checklist, but still the incident has happened more than once.

As an aside, I have many thousands of hours on A319, A320, A330 and A340 aircraft having flown them since 1992 and not only think the aircraft is superbly designed and exceptionally well-thought out but having had my share of abnormalities and "interesting situations" in Airbus aircraft over the years as well as abnormal situations which, had they been slightly different, had the potential to overwhelm a crew with information-overload, I have never seen the capriciousness which at times is so heavily attributed to the design in some of the posts here and, it seems interminably, elsewhere. It is a tiresome dialogue with little potential for settling to the agreement of all, the point of the comments being, it appears, just a good public joust instead. (I have also thousands of hours on Boeing 727/767 as well as Douglas DC8, DC9 and L1011's and they compare favourably but not better or worse, just different - each with its idiosyncracies which must be learned and accomodated by professional crews).

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