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AF 447 Thread no. 4

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AF 447 Thread no. 4

Old 16th Jun 2011, 16:40
  #41 (permalink)  
 
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Cool

Hi,

Like some others, I have a feeling that the PF may have experienced some difficulty in achieving left-stick without up-stick when unexpectedly handed the baby at 4am CET. I also hang on to the faint hope that the BEA may acquire ASI 2 data from the QAR. Unless it was over-reading, I cannot understand why he perpetuated the mistake as the aircraft climbed.
The BEA note:

From 2 h 10 min 05 , the autopilot then auto-thrust disengaged and the PF said "I have the
controls". The airplane began to roll to the right and the PF made a left nose-up input. The stall
warning sounded twice in a row. The recorded parameters show a sharp fall from about 275 kt
to 60 kt in the speed displayed on the left primary flight display (PFD), then a few moments
later in the speed displayed on the integrated standby instrument system (ISIS).
Note 1: Only the speeds displayed on the left PFD and the ISIS are recorded on the FDR; the speed
displayed on the right side is not recorded.
Note 2: Autopilot and auto-thrust remained disengaged for the rest of the flight.
At 2 h 10 min 16, the PNF said "so, we’ve lost the speeds" then "alternate law […]".
Note 1: The angle of attack is the angle between the airflow and longitudinal axis of the airplane.
This information is not presented to pilots.
Note 2 : In alternate or direct law, the angle-of-attack protections are no longer available but a
stall warning is triggered when the greatest of the valid angle-of-attack values exceeds a certain
threshold.
The airplane’s angle of attack increased progressively beyond 10 degrees and the plane started
to climb. The PF made nose-down control inputs and alternately left and right roll inputs
. The
vertical speed, which had reached 7,000 ft/min, dropped to 700 ft/min and the roll varied
I don't know (or on what they base their feeling) why many people think the pilot perpetuated command to climb ... as the BEA note is clear about ...

The airplane’s angle of attack increased progressively beyond 10 degrees and the plane started
to climb. The PF made nose-down control inputs and alternately left and right roll inputs
BTW .. exactly like the Perpignan pilote made.
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Old 16th Jun 2011, 17:24
  #42 (permalink)  
 
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Tail chute:

Probably a very bad idea. Aside from the complexity of certifying such a thing (presumably a different design/size would be needed for each aircraft type), the risk of inadvertent deployment causing it's own disaster would seem much more likely than the incredibly rare situation where it might be of positive benefit.

As far as I can tell from what we know to date, the crew were not aware they were in a stall (you'd have assumed someone would have used the words "we're in a stall" and that the BEA would have reported such in the note) and as such it seems unlikely they would have "punched the button" to deploy such a thing.
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Old 16th Jun 2011, 17:28
  #43 (permalink)  
 
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A sustained nose down input would have done the trick. No need to reinvent the wheel.
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Old 16th Jun 2011, 17:33
  #44 (permalink)  
 
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Originally Posted by jcjeant View Post
The airplane’s angle of attack increased progressively beyond 10 degrees and the plane started
to climb. The PF made nose-down control inputs and alternately left and right roll inputs
The note also says:

Originally Posted by BEA note
After the autopilot disengagement:
  • the airplane climbed to 38,000 ft,
  • the stall warning was triggered and the airplane stalled,
  • the inputs made by the PF were mainly nose-up,
  • the descent lasted 3 min 30, during which the airplane remained stalled.
  • The angle of attack increased and remained above 35 degrees,
  • the engines were operating and always responded to crew commands.
which *implies* (but does not explicitly state) that the nose-down inputs were outweighed by the size and/or frequency of the nose-up inputs made. The implication to pilots who find themselves in that unenviable situation would therefore be to hold nose-down input long enough for the autotrim to neutralise the nose-up setting that it had previously commanded or to use manual pitch trim if you want to be certain of where the THS is positioned by directly controlliing it mechanically.
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Old 16th Jun 2011, 17:40
  #45 (permalink)  
 
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RR NDB, 38
It would be better "written off" a/c´s than other similar tragedies.
It it saved one life, it would be worth it, imho, though you would never get
the beancounters or actuarial types to agree, who just factor in the occasional
hull loss into the risk assessment. Cruel old world, but that's business.

Chris Scott, 39
Presumably a tail-chute could be fitted, perhaps to a strengthened APU bulkhead.
How its getting tangled-up with the APU (which might be running) could be
prevented, I'm not sure.

Other problems
(1) It would have to be certificated for public transport, and presumably deployed on a test-flight.
(2) Would it be deployed automatically or manually (by crew action), and what criteria would be used?
(3) Would it subsequently be jettisoned automatically or manually (by crew action), and what criteria would be used?
(4) In the event of jettison failure, which might have followed unwanted deployment, would the aircraft be capable of maintaining level flight? (The second prototype BAC 1-11 had to make a very sudden forced landing on Salisbury Plain when it suffered this problem during deep-stall testing,)

Hard cases make bad law?
There would be difficulties, but apart from the politics, the rest is just an
engineering problem and it is proven technology elsewhere. Not to make light
of it all, but if there was the will, the job would get done. Hard cases can
make bad law, but that's not an excuse for doing nothing.

A serious problem for airbus and others is that the fitting of a tail
chute or any radical stall recovery solution would be an indirect admission
that their planes can stall, when they have spent so many years carefully
crafting and disseminating the myth that they cannot. They don't even train
for it, it can't happen, so don't worry. Seems to me that they have been
drinking far too much of their own koolaid, but perhaps i'm completely wide
of the mark with that view. Just don't mention the war, right ?.

If you consider that all the fbw technology filtered down initially from
military requirements, where it was tested to the limit in every way, you
could argue that civil aviation currently has only half the deal. Fbw
technology allowing relaxed stability requirements as per mil, but in
reality no way to get it all back if the envelope is pushed just that little
bit too far.

Someone posted a link to the 320-232, D-AXLA video earlier and watching it,
was surprised by the speed and quantity of input from the pilot on the stick.
With a weight of (?) 200 tons, it would take seconds to get any significant
response, or am I way off beam ?...
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Old 16th Jun 2011, 17:41
  #46 (permalink)  
 
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jcjeant:

I don't know (or on what they base their feeling) why many people think the pilot perpetuated command to climb ... as the BEA note is clear about ...

The airplane’s angle of attack increased progressively beyond 10 degrees and the plane started
to climb. The PF made nose-down control inputs and alternately left and right roll inputs
BTW .. exactly like the Perpignan pilote made.
What does this mean then from the very first paragraph at the START of the incident:

The airplane began to roll to the right and the PF made a left nose-up input
What do you imagine this did if it didn't precipitate a climb?

Perhaps I'm way off here, but clearly this ISN'T the first time an AP and AT has dropped out while in cruise at FLxxx (please, correct me if I'm wrong), but given there are no other reports of those aircraft not making it to their intended destinations, my assumption is this is not considered a particularly problematical situation in the normal run of things.

Agreed this situation was precipitated by a loss of pitot data, resulting in a loss of speed inputs, but the point is at moment (x) the airplane is cruising fairly normally under full auto control and some short time later (y) things have gone rather wrong under PF command. The BEA have provided what they consider is key relevant data/information in the form of the published note, with the full understand that this document was likely to be hyper-analyzed by some small segment of the aviation community in particular, knowing that eventually the full details will be released. So it seems very implausible that the information provided is not the fundamental framework of the whole event.

AP/AT off, roll to the right, PF left NU input, climb....

I think trying to paint a mysterious picture on top of this is erroneous and misleading. My presumption from what you have written, your are implying the climb was NOT of the pilots command? I can see nothing to support that assertion.
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Old 16th Jun 2011, 18:30
  #47 (permalink)  
 
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Re.: Parachute problems, flight test challenges, and AOA sensors problems (Emphasis mine):

...According to statements from the surviving co-pilot and flight test engineer, the flight crew was troubleshooting a noise associated with stalls conducted during previous flight test activities. A non-scheduled stall was conducted after the scheduled testing and the plane's angle of attack, the difference between the plane's flight path and its wing's chord line, increased past the maximum allowance of 34 degrees.

All is Lost...

The flight crew lost control of the Challenger. Following the recovery procedures set in place, they were unable to regain control, going so far as to, in a last ditch effort, deploy the plane's emergency spin recovery parachute. Control was temporarily regained, but now the deployed chute fouled the flight characteristics. Unable to release the chute, with with the plane's starboard engine failing, the flight crew was forced to bail out of the doomed aircraft.

The plane impacted the desert floor near the village of Cantil at 9:10 in the morning. Unfortunately, the pilot, Eric Norman Ronaasen, was killed when his chute failed to deploy, and the copilot, Dave Gollings, received minor injuries. The flight test engineer, Bill Scott, was not injured

Months after the crash, a Canadair flight engineer examined computer information that had been available before the crash and discovered the banging was caused by an engine problem.

The NTSB, after its investigation, concluded the probable cause of the accident was a problem with the angle-of-attack indicator binding, due to a failure in the seals of the hydraulic system. It also concluded that four separate systems failures had caused the crash - three of which had plagued the twin-engined jet in earlier tests.....
Challenger #1001
.
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Old 16th Jun 2011, 18:38
  #48 (permalink)  
bearfoil
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"The airplane began to roll to the right and the PF made a left nose-up input"

How much climb? Was he reacting to FD or VSI? BEA themselves say that the a/c didn't "start to climb" (Why do you assume it "started to climb" from level?)until the NU was passing through ten degrees NU. The pilot made one NU (one) input. Was he (attempting) correcting for a natural ND tendency (or, stopping a descent?) that the a/p had been solving, but at drop, the a/p input was stopped? (Yes?, since the a/p stops at quit; there are no more "trend" solutions). Since he then is described as inputting several ND inputs, was he attempting to control an opposite, and again, (perhaps) "natural tendency" for NU? Under what circumstances can the PF be overridden by Trim? He had attitude (supposedly) so what was the disagree between PF and THS? (If any). If at any time PF was aware of an NU of ten+ degrees, he tries to climb exactly Why? BEA have left the barn door open, and the ensuing nonsense on either side allows Airbus to relax at PAS?

It is just as easy for me to believe the THS went into banana mode as it is for PF (F/O1) to be thought to be wired backwards.


The airplane’s angle of attack increased progressively beyond 10 degrees and the plane started to climb. The PF made nose-down control inputs and alternately left and right roll inputs..
Trying to see where in the report the PF can be faulted for a THS at 13.2 degrees.

Last edited by bearfoil; 16th Jun 2011 at 18:53.
 
Old 16th Jun 2011, 18:42
  #49 (permalink)  
 
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sidestick vs control column

...And you certainly do not continue pulling...
Lots of theories here about the chances to recover from a deep stall.

However it took quite some time to get the Bus INTO that condition, with obviously a lot of confusion going on (climb 3000ft without noticing?).

If the PF on a machine with conventional control column starts to pull when the A/C is already in a stall condition, the second set of eyes on the flight deck will most likely immediately realise the mistake, he will shout, take control, assist,... at least do something useful.

When the PF of an AB type fiddles around with his sidestick, the PNF obviously has only very limited information about what his colleague is doing.

Especially in a high-tension situation, where you find yourself in the middle of a CB, a moving column in front of myself pleases me much more than a frozen sidestick, that does not reflect the inputs of the PF.

I suppose that endless believe in the ability of the flying computer to cope with all posible scenarios and elliminating one of the principals: Keeping the crew in the loop proved to be one of the main killers...

I guess before Airbus there were not many stick-piloted aircraft with 2 crew (from PZL´s Blanik till Rockwell´s famous glider) that did not give the second crew member a feedback on his stick from the inputs of the other pilot!
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Old 16th Jun 2011, 18:49
  #50 (permalink)  
 
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Originally Posted by FA10 View Post
I guess before Airbus there were not many stick-piloted aircraft with 2 crew (from PZL´s Blanik till Rockwell´s famous glider) that did not give the second crew member a feedback on his stick from the inputs of the other pilot!
Lordy, lordy... If the PNF was unhappy with the developing situation - indeed if any PNF is unhappy, on a FBW Airbus all they have to do is state "I have control" and push the button on their own sidestick, which will immediately transfer full control to the other side of the flight deck.

In an aircraft that has manual reversion, there are many circumstances when being able to monitor the other pilot's inputs (and the aircraft's responses) is helpful. In a fully-hydraulic aircraft those circumstances are fewer. While the Airbus philosophy restricts more information to the visual channel, the presence of 3 ADIs should be more than enough to determine that things are not going well in terms of the aircraft's attitude.
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Old 16th Jun 2011, 18:58
  #51 (permalink)  
 
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Originally Posted by jcjeant View Post
Hi,

The BEA note:

I don't know (or on what they base their feeling) why many people think the pilot perpetuated command to climb ... as the BEA note is clear about ...

The airplane’s angle of attack increased progressively beyond 10 degrees and the plane started
to climb. The PF made nose-down control inputs and alternately left and right roll inputs
BTW .. exactly like the Perpignan pilote made.
You need to read the english more carefully (and that might not be easy for non-natvie speakers, not sure I could read the French exactly right).
BEA haven't helped by releasing this as a narrative rather than a simple time-line - but then it isn't an investigative report, it's a press release designed to shut up the distressing (for some, I'm sure) media speculation. To be fair, it has largely succeeded in that.

Leaving out the other stuff, the sequence of pilot input and plane response reads like this:
  • PF left nose-up input
  • ptich increases, plane starts to climb
  • vertical speed reaches 7000fpm
  • PF makes nose-down inputs
  • vertical speed reduces
The 7000fpm figure appears after the nose-down input in the text, but is qualified with "which had reached", meaning that figure being already reached at the time of the nose-down input.

This timeline is why "people think the pilot perpetuated command to climb" - because there is no indication of anything else, and when the pilot input went nose down the plane responded.
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Old 16th Jun 2011, 19:04
  #52 (permalink)  
 
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Hi jcjeant,

The BEA Update is written in plain language, and time-markers are very limited. There is much room for interpretation (that is, ambiguity). That is why many of our best contributors here are either silent, awaiting the full data, or contributing but rarely.

You have chosen to interpret it in a way which supports your pre-conception that the upset was likely to have been caused by a fault in the Airbus FBW system. Good luck to you. As you would expect of an ex Airbus skipper, I look at it from a different perspective: was it weather, system fault, or pilot mishandling in difficult circumstances; or some combination of these factors?

Remember, the BEA states that, after the AP disengaged,
"the airplane began to roll to the right and the pilot made a left nose-up input",
but it doesn't say how long the nose-up input lasted.

I think the clue lies in the next paragraph, dealing with the initial climb, of which you have only quoted the first part. Here is all of it:

"The airplane's pitch attitude increased progressively beyond 10 degrees and the plane started to climb. The PF made nose-down control inputs and alternately left and right roll inputs. The vertical speed, which had reached 7000ft/min, dropped to 700ft/min and the roll varied between 12 degrees right and 10 degrees left. The speed displayed on the left side increased sharply to 215 kt (Mach 0.68). The airplane was then at an altitude of about 37,500 ft and the recorded angle of attack was around 4 degrees."
[my highlighting]

So, a likely interpretation is that the PF's nose-up input initiated the climb by increasing pitch to above +10deg. (You may disagree.) That is an extraordinary attitude at high altitude. He may have ceased nose-up inputs at that point, but the new pitch attitude produced a climb VS of 7000ft/min. At that rate, it would only take about 15 seconds to get to the next point, where the PF made his short-term nose-down input, causing the reduction in VS to only 700ft/min with an AoA of +4, which was just below the stall AoA.

At this stage, the situation was already very serious and very tricky to stabilise, and it is easy to criticise with armchair hindsight. However, had he maintained some forward stick for a bit longer, a descent would have started and the aeroplane would not have stalled. His altimeter should have been not more than a few hundred feet in error, so he would have known he was too high. A gentle descent with the nose somewhere near the horizon would have been a step in the right direction. The pitch-up tendency caused by the selection of TOGA thrust would have been countered by the FBW system applying down-elevator, backed up by the THS.

Unfortunately, according to the BEA, the PF's next pitch commands were nose-up. The reason for that is unclear, but that is what led to the stall.
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Old 16th Jun 2011, 19:06
  #53 (permalink)  
 
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Trust me, DozyWannabe, I know how to take controls - have to do it occasionally.

...the presence of 3 ADIs should be more than enough to determine that things are not going well...
...maybe there is a generic problem in that assumpion?
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Old 16th Jun 2011, 19:08
  #54 (permalink)  
 
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Originally Posted by syseng68k View Post
A serious problem for airbus and others is that the fitting of a tail
chute or any radical stall recovery solution would be an indirect admission
that their planes can stall, when they have spent so many years carefully
crafting and disseminating the myth that they cannot.
As opposed to the direct admission of designing and building in a full stall warning system ? Did they do that just for fun on their day off, being as it wasn't in-spec ?

Those that designed the a/c clearly knew it could stall. Whether that message got messed up between there and the people that train the pilots that fly it, is another more interesting question.
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Old 16th Jun 2011, 19:18
  #55 (permalink)  
 
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Sidestick

Quote from syseng68k:
Someone posted a link to the 320-232, D-AXLA video earlier and watching it, was surprised by the speed and quantity of input from the pilot on the stick. With a weight of (?) 200 tons, it would take seconds to get any significant response, or am I way off beam ?...

No, you are right. In case you haven't seen it before, here is my opinion:

http://www.pprune.org/tech-log/31609...ml#post3979423
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Old 16th Jun 2011, 19:34
  #56 (permalink)  
 
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Originally Posted by FA10 View Post
Trust me, DozyWannabe, I know how to take controls - have to do it occasionally.
I wasn't implying you didn't, I was just throwing that information out there, apropos of nothing...

...maybe there is a generic problem in that assumpion?
I'd say that the very respectable safety record of the FBW Airbus series suggests otherwise, but that's just my opinion.
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Old 16th Jun 2011, 19:40
  #57 (permalink)  
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Ten degrees nose UP? That tells us nothing about the AoA, or the position of the THS. Was it already at 13.2? Did pilot cease his initial NU and begin his repeated ND inputs? The 7000fpm suggests the climb was (initially) very rapid, and there is no reason to think the THS was not "UP" having corrected for a chronic descent? Turbulence? There is nothing in this sequence (sic) to base a conclusion of PF chronic NU. BEA say ".......A INPUT....."

How outlandish was the descent that THS needed ten degrees to arrest it, and start to climb? Or more to the point, what was the THS' deflection at a/p drop? BEA don't say. A/P will hang in until 13 degrees Pitch UP before it quits. If the descent was transient, and chronic, why shouldn't the THS react with 13 degrees nose up? FOR TRIM.... Initially, PF may have seen the nose dropping as the problem needing nose up. When he realised his TRIM state, he started his repeated ND?

you say,

So, a likely interpretation is that the PF's nose-up input initiated the climb by increasing pitch to above +10deg. (You may disagree.) That is an extraordinary attitude at high altitude. He may have ceased nose-up inputs at that point, but the new pitch attitude produced a climb VS of 7000ft/min. At that rate, it would only take about 15 seconds to get to the next point, where the PF made his short-term nose-down input, causing the reduction in VS to only 700ft/min with an AoA of +4, which was just below the stall AoA.
What About.....

IOW. If the THS was at 13.2 degrees at a/p handover, and the a/c was sinking, wouldn't the PF input NU to stop descent? When he realizes his THS (can he?), he stops, but the a/c "has started to climb" (Bow Howdy, 7000fpm?) His elevator pushed the a/c past what it needed? Once climbing, furtrher ND input stalled the TAIL AS A UNIT. It could not bite to drop the nose, It was committed to Ballistic trajectory to actual aerodynamic Stall, that dropped the Nose but no energy available to keep the nose dropping so it settled back on its tail., but PF input ND, which restalled the TAIL. Now PF is in a corner. He CANNOT recover, he is bracketed between no energy and a Tail that cannot unstall. The tail is a huge Spoiler, now, and it is stuck deployed full. When the a/c goes NU , it is limited by the drag of the tail from going inverted, but since the Tail cannot unstall the a/c cannot drop. This I believe was the result of what is seen as the initial "recovery" that initiated the STALLSTALL. The AoA was never going to be less than 4 degrees, insufficient to Break the STALL.

This means that the THS may have been responsible for the A/P quitting. 13.2 degrees exceeds its Limit for TRIMMING. Does Airbus want such a huge lifting surface as a TRIM DEVICE? Pending further data, it could well be.

Why did the Pilots not MAN TRIM ND? First of all, they were trained not to, and secondly, How were they to know the THS was at 13.2 degrees NU or at the limit. Actually, BEA have not said precisiely. With elevators, they had horrible nose up, or "almost" a recovery. The Rolling on descent may have been there solution to gain STALL recovery.

There is just such a disconnect between a/c and pilot, is it impossible to entertain "holding back stick all the way down"? Every time they Push, the a/c goes berserk, and refuses to unSTALL anyway. Holding back stick gives a stable, "quiet" ride. Deadly, but quiet.


The LEFT ROLL command? Let's say the Autopilot had been trimming for NU and Right ROLL. Just before a/p quits, the trend intensifies, perhaps with gusto. Serious ND trend and right ROLL. These aspects can be as much as 9 degrees ND and 45 degrees ROLL. The a/p quits with max NU and max left ROLL. PF is not ready for this amount of Trim; his initial (and likely ham handed, as discussed) inputs ask for maximum Left Roll and Maximum NU.

Hell of a way to start flying. In an astonishing climb, where ND inputs stall the Tail, and the trajectory is ballistic. Ballistic because no aerodynamic controls were available to descend, and the climb will only halt when the energy is too small to fly, only ballistic flight,

I am not sure the PF was not trying to keep the nose dropping when the AoA was 4 degrees, but the Plane couldn't get over the last little bump.

Last edited by bearfoil; 16th Jun 2011 at 20:38.
 
Old 16th Jun 2011, 19:40
  #58 (permalink)  
 
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Trust me, DozyWannabe, I know how to take controls - have to do it occasionally.


Quote:
...the presence of 3 ADIs should be more than enough to determine that things are not going well...
...maybe there is a generic problem in that assumpion?
Totally agree, while 3 ADIs might give a strong "hint" that things are not going well to the PNF they do not provide all of the data needed to understand the situation.

Specifically while it might be very obviouse that something was wrong the PNF would have no way of knowing that the PF might be making inputs contrary to what the situation seemed to warrant.

This could well delay the PNFs response since he might hesitate to ask a seemingly insulting question such as "we appear to be stalled, which way are you pointing the nose?" and instead assume the PF was dealing with a more arcane situation.

With direct knowledge of the PF inputs the PNF would be better able to recognize human as well as system failures.

BTW: I -do not- think the cause is anywhere close to pure pilot error, the above is meant as an example of need for awareness of -all- inputs affecting the aircraft.

---

The statement that "XXX cases of UAS at altitude did not have bad outcomes" is depressingly reminscent of NASAs attitude towards O ring erosion on the booster rockets.

In both cases a primary safety device was comprimised but disaster was prevented (for a while) by what was supposed to be a backup.
(O rings on shuttle, pilots and pitch/power on airplanes).

Last edited by MurphyWasRight; 16th Jun 2011 at 19:52. Reason: Typos, clarity.
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Old 16th Jun 2011, 20:13
  #59 (permalink)  
bearfoil
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THIOKOL refused to OK the Launch due Weather. "Light this Candle" (Alan Shephard). They launched, and Thiokol, though grim, dodged a bullet.

The Launch was manslaughter. (Challenger Hearings, Feynman).
 
Old 16th Jun 2011, 20:20
  #60 (permalink)  
 
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THIOKOL refused to OK the Launch due Weather. "Light this Candle" (Alan Shephard). They launched, and Thiokol, though grim, dodged a bullet.

The Launch was manslaughter. (Challenger Hearings, Feynman).

bear
Actually Thiokol -engineers- said no but were overuled by Thiokol -managers- and NASA in the infamous conference call.

The point though is that like the UAS the O ring erosion was a known issue that was swept under the rug with "nothing bad has happened" etc.

BTWW Same thing for tile damage from foam shedding from the external tank, that is the really tragic one since NASA reverted to their old behavior of justifying exceptions since they had not caused problems in the past.
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