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Old 2nd Oct 2007, 08:31
  #2621 (permalink)  
Join Date: Sep 2000
Location: Bielefeld, Germany
Posts: 955

we've been through a lot of this already when discussing the FDR. It appears we have a couple new people, who maybe have not seen the FDR transcript. I will refer to
for a link to it, the CVR, and a Why-Because Analysis from the available data.

I'll restrict myself to the technical details.

Originally Posted by electricjetjock
The pilot flying left the thrust lever in the CLB detent NOT the aircraft or designers.
Originally Posted by RWA
That's maybe 80% probable, but not certain. All we know is that the FDR recorded the lever as being in CLB.
A more accurate statement would be that it is 99.9999999% probable, but not certain. I believe that mechanism is a 10^(-9) certification item and I have a query out on that to one of the four JAA certification teams.
Originally Posted by RWA
Try as I might, I've never been able to fully to understand AB's various 'modes'
The scare quotes are a good idea. "Mode" is a technical term that refers to AP and AT operations.

Here may be the point to respond to ChristiaanJ's comment that analogue and digital FBW are functionally the same. Yes, you can theoretically reproduce all digital logic with analogue logic or cables, pulleys and bell cranks, because the "logic" is basically design, which just happens to be more trivial to implement in digital electronics than with pulleys and bell cranks. However, digital FBW and digital autopilots have *modes* and I don't know any planes with analogue FBW that do. (That may not mean much, since I am not an expert on military HW, but that was one of the main design differences when I was working on the SIFT verification 23 years ago.) Modes are a design feature to handle complexity (both combinatorial and cognitive).

Originally Posted by RWA
I believe that another possibility is that the systems would have considered any setting above 'Idle' as being the next detent up (i.e. CLB).
That's too vague for me to be sure what you mean. Here are the relevant FCOM citations
Originally Posted by Power Plant: 1.70.30 p2
If the thrust lever is set between two detents, that FADEC selects the rating limit corresponding to the higher detent.
Just what the FADEC does with this rating limit is another issue. I think the relevant point here is what counts as "Idle" position for the ground spoilers when you are landing, and the answer is
Originally Posted by Flight Controls: 1.27.10 p13
For the ground spoiler logic, idle signifies: Thrust lever position < 4 or < 15 when below 10 ft [radio altitude]
Originally Posted by RWA
The possibilities are ...... or he may have knocked it forward while reaching over it to get hold of and lift the reverser latch on No. 1.
No. This is not a relevant possibility. The FDR shows no significant variation of any sort in TLA #2 from approach to end of recording.

Originally Posted by electricjetjock
He also did not immediately apply full manual braking when autobrake failed.
Originally Posted by RWA
I believe that according to the FDR, the pilot(s)' first step was to recycle the spoiler switch. That's pretty strong evidence that (having got reverse thrust) they thought that they had a spoiler malfunction.
No. First manual braking. Full braking started at 18:48:34 and pedal position was max at 18:48:36 (sampled once a second). Spoilers were unarmed between 18:48:35.5 and 18:48:36 and rearmed between 18:48:47.5 and 18:48:48 (sampled twice a second).

Originally Posted by RWA
my understanding is that applying the brakes at 140 knots would have been next to useless (and could very well have caused more problems than it solved).
We have been over the braking very thoroughly. Manual braking began at 120kts (they lost 10 kts in the first few seconds without) and I calculated an average deceleration of 1.26 m/s/s and at times it was up to 2 m/s/s. Far from being "next to useless", it would have stopped the plane had they had another X meters (estimates vary here), or would have reduced the GS to EMAS-entry speed with a couple hundred more.

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