AF 447 Search to resume
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447 Parted
Bearfoil et al
Surely the Fin/V.S. shows little sign of being ripped off sideways by aeroD forces but
lots of sign of departing by being inertially pulled off by suffering some kind of
massive whiplash ?
I dont quite understand what you are saying by, "radial forces"
I also dont follow the whereabouts or pertinence of your figure, "1.5G failure"
Thanks
Surely the Fin/V.S. shows little sign of being ripped off sideways by aeroD forces but
lots of sign of departing by being inertially pulled off by suffering some kind of
massive whiplash ?
I dont quite understand what you are saying by, "radial forces"
I also dont follow the whereabouts or pertinence of your figure, "1.5G failure"
Thanks
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Bearfoil ...
The a/c is designed for structural limit load at 1.51 G. Two G buys the farm.
IMHO the brick wall was not the 90 degree to line of flight one, but the one vertically below the line of flight, i.e. Terra Oceania. Any deformations to the left and forward of line of flight (at point of impact) are the result of small moments along those vectors that also suddenly accelerated to zero.
mm43
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wilyflier
FAR 25- structural load/limit load @ 1.5 no deformation/failure.
Radial: Torsional
mm43
The Rudder is swept, and the corner of airfoil that failed loaded the mounting lug vertically as a result of its deformed ultimate plane. The pick up arm performs the function of a "strut", see above. That part of the Rudder "pushing" back on the airsteam is largest in area at the lowest lug.
"vertical" as I read the photo is the normal operating movement of the Rudder, relative to the Vertical Stabiliser, vertical as in "about" the horizontal aspect of the Hinge axis. The arm is meant to "spread" the energy at the pivot hinge, to take up some of the "vertical" stress of a deployed Rudder face. "Shear Cracks, Vertical", are indicative of the attachment's failure in its operating plane as well.
It serves to demonstrate an enormous load at the pivot, from a Rudder at some deployment in an airstream, in other words, I feel it is not impact related. We are looking at a Rudder pivot hinge destroyed by Rudder deployment beyond its limit load, i.e. aerodynamic failure.
When you say: "up and down" are you meaning "compression, tension"?
I suggest the vertical cracks in the pin's sheath at the thru-bolt are very consistent with an overloaded Rudder deflected to the right.
bear
FAR 25- structural load/limit load @ 1.5 no deformation/failure.
Radial: Torsional
mm43
The Rudder is swept, and the corner of airfoil that failed loaded the mounting lug vertically as a result of its deformed ultimate plane. The pick up arm performs the function of a "strut", see above. That part of the Rudder "pushing" back on the airsteam is largest in area at the lowest lug.
"vertical" as I read the photo is the normal operating movement of the Rudder, relative to the Vertical Stabiliser, vertical as in "about" the horizontal aspect of the Hinge axis. The arm is meant to "spread" the energy at the pivot hinge, to take up some of the "vertical" stress of a deployed Rudder face. "Shear Cracks, Vertical", are indicative of the attachment's failure in its operating plane as well.
It serves to demonstrate an enormous load at the pivot, from a Rudder at some deployment in an airstream, in other words, I feel it is not impact related. We are looking at a Rudder pivot hinge destroyed by Rudder deployment beyond its limit load, i.e. aerodynamic failure.
When you say: "up and down" are you meaning "compression, tension"?
I suggest the vertical cracks in the pin's sheath at the thru-bolt are very consistent with an overloaded Rudder deflected to the right.
bear
Last edited by bearfoil; 1st Mar 2010 at 21:44.
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Bearfoil, have it your way. NOW, duplicate the damage twisting to the side, eh?
It does not require severe acceleration if the tail of the plane is bent upwards. That produces a relatively speaking slow rip that pops the VS off. I am quite aware of how it is attached having seem cutaway diagrams and such. As you mention a simple sudden cessation of forward movement would not produce what is seen.
As one possible scenario, it looks like the tail cone broke off at its natural break point, the junction with the pressure vessel of the cabin. It was pushed upwards. This applied tremendous force to the trailing edge of the VS as the spar that holds the clevis joints which mount the tail is bent. The nose of the VS is held in place by the relatively strong pressure vessel. Where does the VS go? All that can happen is that you get tears approximately the same as what you see on photos of the plane. There is even a good reason for the front joint to retain part of the clevis. That's about where the spar would break anyway looking at the drawings.
Now, duplicate those tears with a sideways rip to the rear. They'll come out exactly backwards.
Methinks you are positing actions in the absence of and indeed directly contrary to the evidence, such as we have it.
{^_^}
It does not require severe acceleration if the tail of the plane is bent upwards. That produces a relatively speaking slow rip that pops the VS off. I am quite aware of how it is attached having seem cutaway diagrams and such. As you mention a simple sudden cessation of forward movement would not produce what is seen.
As one possible scenario, it looks like the tail cone broke off at its natural break point, the junction with the pressure vessel of the cabin. It was pushed upwards. This applied tremendous force to the trailing edge of the VS as the spar that holds the clevis joints which mount the tail is bent. The nose of the VS is held in place by the relatively strong pressure vessel. Where does the VS go? All that can happen is that you get tears approximately the same as what you see on photos of the plane. There is even a good reason for the front joint to retain part of the clevis. That's about where the spar would break anyway looking at the drawings.
Now, duplicate those tears with a sideways rip to the rear. They'll come out exactly backwards.
Methinks you are positing actions in the absence of and indeed directly contrary to the evidence, such as we have it.
{^_^}
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I am relying heavily on AA 587's aerodynamic failure and loss of VS/Rudder. That occurred at less than 250 knots, ostensibly with control inputs. Considering 447 was travelling at nearly twice that speed with iffy control, well, let me say there is very little to go on, but I cannot think of a better witness to the tragic accident than a complete VS/Rudder. If it stayed with the a/c until impact, you are challenged with a two part explanation of its removal, a vertical impact, and a rebound. My surmise needs one explanation, I like the easy way, as did Occam.
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Bearfoil ...
We are looking at a Rudder pivot hinge destroyed by Rudder deployment beyond its limit load, i.e. aerodynamic failure.
We are looking at a Rudder pivot hinge destroyed by Rudder deployment beyond its limit load, i.e. aerodynamic failure.
This means that CAS was 272 +/- 2 KTS, but we don't know what the OAT was, nor if the a/c was at its nominal M0.82, or as the CAS dropped, the A/THR was increasing that speed. So, are you proposing that overspeed could well be responsible for the V/S and Rudder damage? I would have expected to see trailing edge buffet damage if that was the case.
The Port Outer Spoiler was located north and east of most other debris, but that could well be because it was not affected by wind when in the water, and its drift represented the actual near surface current without any leeway component on account of windage.
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mm43
I believe failure signatures on the Rudder hinges are due to aerodynamic loading, not impact with the sea. What is the Rudder Limit in Alt Law II?
It does not matter, as the stress on the Rudder needn't have been the result of it's angle relative to the VS. Severe Yaw is sufficient to fail the rudder's hinges, even with it centered.
I've often wondered why the Rudder's hingeing system is built (overbuilt), with such care. An aircraft can fly and land without a Rudder, it cannot fly at all without a Vertical Stabiliser. Such irony in AA587, the Rudder stayed attached, the VS came off. In the case of 587, if it was indeed FO's feet that snapped the life out of his a/c, a shame the Rudder hadn't fallen off, to leave the VS attached, and take them home.
Yes, I believe the Spoiler was lost before impact.
JD-EE
Sir, would you enlarge on your statement "Swatted the a/c out of the air"? I'm not getting it.
bear
I believe failure signatures on the Rudder hinges are due to aerodynamic loading, not impact with the sea. What is the Rudder Limit in Alt Law II?
It does not matter, as the stress on the Rudder needn't have been the result of it's angle relative to the VS. Severe Yaw is sufficient to fail the rudder's hinges, even with it centered.
I've often wondered why the Rudder's hingeing system is built (overbuilt), with such care. An aircraft can fly and land without a Rudder, it cannot fly at all without a Vertical Stabiliser. Such irony in AA587, the Rudder stayed attached, the VS came off. In the case of 587, if it was indeed FO's feet that snapped the life out of his a/c, a shame the Rudder hadn't fallen off, to leave the VS attached, and take them home.
Yes, I believe the Spoiler was lost before impact.
JD-EE
Sir, would you enlarge on your statement "Swatted the a/c out of the air"? I'm not getting it.
bear
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Bearfoil ...
What is the Rudder Limit in Alt Law II?
What is the Rudder Limit in Alt Law II?
A330 - Yaw. If both SECs are inop, max rudder deflection remains at its last known value and max is only available when slats are extended. 31.6° max is available up to 150kt then reduces to 4° gradually. In the case of total hydraulic failure, the rudder travel is damped so the rudder returns to aerodynamic neutral. In case of total electrical power failure or loss of flight computers, the back up yaw damper unit (BYDU) becomes active for yaw damping functions. After total electrical failure or loss of rudder control due PRIM/SEC fail, the Backup Control Module controls YLO or BLU if YLO inop. THE BCM has its own Backup Power Supply driven by either BLU or YLO hyd. Rudder trim is through 2 electric motors positioning artificial feel units normally through SEC 1 and motor 1 with SEC 2 and motor 2 in synchro as back-up. When activated in alternate yaw, there is no turn co-ordination.
mm43
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Bearfoil, I mean that in a literalist sense.
mm43 has performed excellent analysis indicating that the plane hit the water about where it was four minutes before it ceased ACARS transmissions. Actual indications are North West of that point by some modest amount - at right angles to the nominal flight path. The plane was traveling at a speed that requires 25 seconds at 1 g to bring it to a stop. That's a few miles to the North East of where it was when the troubles began.
What halted its forward velocity vector and pushed it North Westwards by a goodly amount? I don't know.
One scenario, presuming mm43's work is good, has the plane making a 180 degree turn starting slightly before that last position report just before everything turned to poop. They hit the water about where such a turn would have placed them had they
managed to complete it while rapidly losing altitude. That, of course, begs the question, "But why?"
Something applied an awful lot of energy to the plane if it simply made that last position report and then sank down to the water in a flat spin with or without a vertical stabilizer and rudder. I am not sure what could have done that. I could see such a loss of control, flat spin or spinless spin, and all that scenario if the ocean tracks of the wreckage traced back to a point further to the North East along the planned flight path. In fact that is a scenario I entertained and partially accepted until the estimates of the impact point based on found wreckage started coming in. Then I put two and two together. If the VS was ripped off in the air the pattern of the rip in the tabs that fit into the clevis joints would be quite different. Damage to the sides of the VS at the bottom would be different. So I had to discard the idea in the face of data.
I am left guessing. You've heard my best guess. You don't like it. *I* would take that as a personal challenge to put the entire body of knowledge we've generated on the wreck and figure out another working scenario. Sadly, I've pretty much used up my imagination. I'm not happy with that tail cone scenario. But, it does almost fit the data. - Plane comes down tail low. Tail hits the water and is pushed upwards and applies a sudden deceleration to the plane. This leads to a water-skier's belly-flop. (This is such as you see when his skis dig into the water for some reason. Vertical person becomes horizontal person rather quickly and forward motion ceases.) The push upwards is worst at the tail. That applies a fracture stress to the tabs as the VS leading and trailing edges are pushed upwards and forward relative to the spar. I figure this all took place at a low forward speed to begin with. And it might give an impression from the wreckage of having a flatter approach to the water than actually took place. (I romantically envision the crew desperately trying to gain enough air speed to restart stalled engines. Maybe they made it. But they were too low and clipped the water trying to climb out of their dive. My cynical side says, "Prove it.")
Maybe that embellishment gets across what I see in my mind's eye better.
We have precious little data. So selecting a scenario that violates any of the data we do know becomes highly risky. But scenarios that do fit it all are risky to one's sanity, I fear.
What stopped the plane in mid air within a very short distance and threw it to the left of its track a not inconsiderable distance?
added:
I'll stop here. If this description does not do the job then continued talking past each other is counter productive.
{^_^}
mm43 has performed excellent analysis indicating that the plane hit the water about where it was four minutes before it ceased ACARS transmissions. Actual indications are North West of that point by some modest amount - at right angles to the nominal flight path. The plane was traveling at a speed that requires 25 seconds at 1 g to bring it to a stop. That's a few miles to the North East of where it was when the troubles began.
What halted its forward velocity vector and pushed it North Westwards by a goodly amount? I don't know.
One scenario, presuming mm43's work is good, has the plane making a 180 degree turn starting slightly before that last position report just before everything turned to poop. They hit the water about where such a turn would have placed them had they
managed to complete it while rapidly losing altitude. That, of course, begs the question, "But why?"
Something applied an awful lot of energy to the plane if it simply made that last position report and then sank down to the water in a flat spin with or without a vertical stabilizer and rudder. I am not sure what could have done that. I could see such a loss of control, flat spin or spinless spin, and all that scenario if the ocean tracks of the wreckage traced back to a point further to the North East along the planned flight path. In fact that is a scenario I entertained and partially accepted until the estimates of the impact point based on found wreckage started coming in. Then I put two and two together. If the VS was ripped off in the air the pattern of the rip in the tabs that fit into the clevis joints would be quite different. Damage to the sides of the VS at the bottom would be different. So I had to discard the idea in the face of data.
I am left guessing. You've heard my best guess. You don't like it. *I* would take that as a personal challenge to put the entire body of knowledge we've generated on the wreck and figure out another working scenario. Sadly, I've pretty much used up my imagination. I'm not happy with that tail cone scenario. But, it does almost fit the data. - Plane comes down tail low. Tail hits the water and is pushed upwards and applies a sudden deceleration to the plane. This leads to a water-skier's belly-flop. (This is such as you see when his skis dig into the water for some reason. Vertical person becomes horizontal person rather quickly and forward motion ceases.) The push upwards is worst at the tail. That applies a fracture stress to the tabs as the VS leading and trailing edges are pushed upwards and forward relative to the spar. I figure this all took place at a low forward speed to begin with. And it might give an impression from the wreckage of having a flatter approach to the water than actually took place. (I romantically envision the crew desperately trying to gain enough air speed to restart stalled engines. Maybe they made it. But they were too low and clipped the water trying to climb out of their dive. My cynical side says, "Prove it.")
Maybe that embellishment gets across what I see in my mind's eye better.
We have precious little data. So selecting a scenario that violates any of the data we do know becomes highly risky. But scenarios that do fit it all are risky to one's sanity, I fear.
What stopped the plane in mid air within a very short distance and threw it to the left of its track a not inconsiderable distance?
added:
I'll stop here. If this description does not do the job then continued talking past each other is counter productive.
{^_^}
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Lots of pointless deliberation hereabouts about the configuration/attitude etc of AF447 at impact. I'd suggest that it's fairly obvious that it spun in in a flat spin - and that airbrakes/speedbrakes/spoilers (at least) were deployed out of desperation. It's more productive to backtrack to why/how this accident happened..... particularly as they are unlikely to ever recover the DFDR (or CVR). The effort this month is in reality a nominal and token, yet enforced, one. It has only a very slim chance of any success.
.
from the post by Noelbaba (The Last Four Minutes Of Air France Flight 447 ). This exposition is a confused mish-mash - and if it has an authoritative sourcing, it is indicative of an attempt to muddy the waters with a welter of disinformation.
.
Three critical aspects mentioned, yet hidden away (and AFAIK) not yet commented upon indepth here on Pprune, still require logically derived answers:
QUES: 1. How does this falsely high reading of TAT affect the ADIRS speed-readouts/data inflows? (if at all) i.e. before considering the Thales pitots' complications?
2. Is it possible that the TAT sensor's heating can be overpowered by an accretion of supercooled ice crystals to the same extent as the Thales pitot heads' pitot heaters?
.
ANSWERS: (probably duff, but that's why I'm asking): -
Answer: 1. If the ADIRS TAT data inflow is falsely high then that (at a constant thrust and IAS) would generate a lower TAS, but that high temp wouldn't affect the IAS (which is after all what predicates the aerodynamic stall speed). "To hold a constant Mach Number (considering that temperature is decreasing and TAS increasing thus MN increasing) you would have to raise the nose (reduce your IAS/CAS) and increase your angle of attack to climb at a constant Mach Number/hence IAS decreases?"
Again, temperature has no effect. At a constant Mach Number climb, both CAS and EAS are reducing, and increasing Angle of Attack is required. The logical extrapolation of this is that if you maintained a climb at constant Mach Number, assuming that you had a lot of excess thrust, you would climb all the way to where the AoA went all the way to the stall. What you have to remember is that the Airspeed Indicator measures Impact Pressure, which is the total sum of Dynamic Pressure (related directly to EAS) and compressibility (related directly to Mach Number). It does not measure Density, which is related to Pressure and Temperature. In fact, all of the manometric instruments on the aircraft, the ASI, Mach-Meter, Altimeter, and VSI only sense Pressure. You, the pilot, have to apply Temperature to Pressure Height to find Density Height and True Altitude, and to CAS and/or Mach Number to find TAS.
During climb, with decreasing pressure, the aircraft must fly faster, i.e. a higher TAS, to achieve the same Impact Pressure, because you're at a constant CAS. This is so, even above the Tropopause where there is no change in temperature with change of Pressure Height (except in the case under consideration here). Because the aircraft is flying faster, compressibility increases, you are experiencing an increasing Mach Number. Note this - On a very hot day, your TAS will be higher due to the lower density AS WELL AS the lower Pressure, but this temperature factor puts you not one jot closer to the speed of sound, because at the higher temperature, the speed of sound (M1.0) is ALSO higher (but, however, NOT in the false TAT case). Thus, the 'hot day effect' of a higher TAS than that due to pressure change alone, has no effect upon Mach Number whatsoever...... but it WOULD HAVE for AF447.
Consider the formula for CAS calibration -
Vc = SQR ((Y/(Y-1)) * Po/Qc * [(Qc/Po+1) ^ ((Y-1)/Y)-1]) * SQR (2 Qc / Rho0)
Where –
Vc = Calibrated Airspeed in ft/sec,
Qc = Impact Pressure in Lb/ft^2,
Rho0 = Sea Level Air Density = .0023769 slugs/ft^3,
Po = Sea Level Air Pressure = 2116.2 Lb/ft^2,
Y = A constant for air = 1.4, being the ratio of the Specific Heat of Air at constant pressure to that at constant volume (Y = Gamma, I don’t have a Greek key-board)
The Left-most portion of the equation is the ‘f’ factor, the compressibility effect –
F = SQR ((Y/(Y-1)) * Po/Qc * [(Qc/Po+1) ^ ((Y-1)/Y)-1])
At altitude, the Static Pressure, P, is substituted for Po in the left-most radical.
Temperature does not even get a mention (except in establishing standard Sea Level Density for calibration purposes, and then it's a constant). However a falsely high temperature might induce the ADIRS to assume a lower thrust and/or TAS/Mach and so cause the autothrust to incrementally offset the (ADIRS) perceived under-performance. Net effect would be to cause AF447 to fly faster than "indicated" (to the pilots) - and thus, in TAS terms, even closer to the coffin corner envelope. You then only need the Thales pitot clog-up over time to create a coffin corner encounter (see theShadow's post at link http://www.pprune.org/rumours-news/3...ml#post5537109 for the outcome of that cumulative {over time} additive error). The conclusion is that a freeze-over of the TAT sensor would have put them, courtesy of the ADIRS, at a higher actual TAS. Usually the temperature isn't a factor or a consideration, except when it's a "phony" one.
.
Also, in this regard, the article claims fairly authoritatively that AF447 was heavy (i.e. cargo and pax-laden) so went early direct to best height (FL350) looking for optimum SFC (i.e. to "make" fuel and avoid any enroute drop-short of destination reserves requirements.). That in itself would have quite early put a heavy AF447 closer than normal to the upper RH edge of the operating envelope and that much closer to a Mach Crit encounter. The fact that they never reported "Level FL350" - but only read-back that final cleared height - may indicate that they levelled and soon thereafter accelerated straight into a compressibility encounter..... having already accumulated some of the icing-induced errors on climb.
____________________________________
Answer: 2. Once again depends (as theShadow points out with respect to the pitot heaters) upon the heating capacity of the sensor's protection. Having atmospheric precipitation freeze upon impact to form ice is quite a different thermal proposition in aviation to accumulating an agglomeration of already formed supercooled ice crystals over time during a relatively smooth cruise in Cirrostratus/Cirrocumulus. But in the Thales pitot head, by contrast, the tendency was to "collect" the ice crystals inside a tube and thus gradually (insidiously) clog the pneumatic flows and sensed pressures. An assumption can be made that a false high TAT (and consequent high undetected TAS), due to a thickening sensor ice-coating, was a possibility.
____________________________________
QUES: 3.
I sorta beg to differ here - entirely. I agree with theShadow that the effect was in fact quite insidious and that all three pitot heads were affected simultaneously and thus never "differed" - (thus no alert to pilots and nil breach of triple redundancy disagreement rules as far as the ADIRS was concerned). See ASW article on the A346 double flame-out due to fuel computer programming: "THRICE ALMIGHTY, the Virtues of Triple Redundancy" (at link
Thrice Almighty - The Virtues of Triple Redundancy | Air Safety Week | Find Articles at BNET
________________________________- Over to others who may be better informed/educated.
.
.
from the post by Noelbaba (The Last Four Minutes Of Air France Flight 447 ). This exposition is a confused mish-mash - and if it has an authoritative sourcing, it is indicative of an attempt to muddy the waters with a welter of disinformation.
.
Three critical aspects mentioned, yet hidden away (and AFAIK) not yet commented upon indepth here on Pprune, still require logically derived answers:
A. Suddenly the gauge indicating the external temperature rose by several degrees, even though the plane was flying at an altitude of 11 kilometers (36,000 feet) and it hadn't got any warmer outside. The false reading was caused by thick ice crystals forming on the sensor on the outside of the plane. These crystals had the effect of insulating the detector. It now appears that this is when things started going disastrously wrong.
2. Is it possible that the TAT sensor's heating can be overpowered by an accretion of supercooled ice crystals to the same extent as the Thales pitot heads' pitot heaters?
.
ANSWERS: (probably duff, but that's why I'm asking): -
Answer: 1. If the ADIRS TAT data inflow is falsely high then that (at a constant thrust and IAS) would generate a lower TAS, but that high temp wouldn't affect the IAS (which is after all what predicates the aerodynamic stall speed). "To hold a constant Mach Number (considering that temperature is decreasing and TAS increasing thus MN increasing) you would have to raise the nose (reduce your IAS/CAS) and increase your angle of attack to climb at a constant Mach Number/hence IAS decreases?"
Again, temperature has no effect. At a constant Mach Number climb, both CAS and EAS are reducing, and increasing Angle of Attack is required. The logical extrapolation of this is that if you maintained a climb at constant Mach Number, assuming that you had a lot of excess thrust, you would climb all the way to where the AoA went all the way to the stall. What you have to remember is that the Airspeed Indicator measures Impact Pressure, which is the total sum of Dynamic Pressure (related directly to EAS) and compressibility (related directly to Mach Number). It does not measure Density, which is related to Pressure and Temperature. In fact, all of the manometric instruments on the aircraft, the ASI, Mach-Meter, Altimeter, and VSI only sense Pressure. You, the pilot, have to apply Temperature to Pressure Height to find Density Height and True Altitude, and to CAS and/or Mach Number to find TAS.
During climb, with decreasing pressure, the aircraft must fly faster, i.e. a higher TAS, to achieve the same Impact Pressure, because you're at a constant CAS. This is so, even above the Tropopause where there is no change in temperature with change of Pressure Height (except in the case under consideration here). Because the aircraft is flying faster, compressibility increases, you are experiencing an increasing Mach Number. Note this - On a very hot day, your TAS will be higher due to the lower density AS WELL AS the lower Pressure, but this temperature factor puts you not one jot closer to the speed of sound, because at the higher temperature, the speed of sound (M1.0) is ALSO higher (but, however, NOT in the false TAT case). Thus, the 'hot day effect' of a higher TAS than that due to pressure change alone, has no effect upon Mach Number whatsoever...... but it WOULD HAVE for AF447.
Consider the formula for CAS calibration -
Vc = SQR ((Y/(Y-1)) * Po/Qc * [(Qc/Po+1) ^ ((Y-1)/Y)-1]) * SQR (2 Qc / Rho0)
Where –
Vc = Calibrated Airspeed in ft/sec,
Qc = Impact Pressure in Lb/ft^2,
Rho0 = Sea Level Air Density = .0023769 slugs/ft^3,
Po = Sea Level Air Pressure = 2116.2 Lb/ft^2,
Y = A constant for air = 1.4, being the ratio of the Specific Heat of Air at constant pressure to that at constant volume (Y = Gamma, I don’t have a Greek key-board)
The Left-most portion of the equation is the ‘f’ factor, the compressibility effect –
F = SQR ((Y/(Y-1)) * Po/Qc * [(Qc/Po+1) ^ ((Y-1)/Y)-1])
At altitude, the Static Pressure, P, is substituted for Po in the left-most radical.
Temperature does not even get a mention (except in establishing standard Sea Level Density for calibration purposes, and then it's a constant). However a falsely high temperature might induce the ADIRS to assume a lower thrust and/or TAS/Mach and so cause the autothrust to incrementally offset the (ADIRS) perceived under-performance. Net effect would be to cause AF447 to fly faster than "indicated" (to the pilots) - and thus, in TAS terms, even closer to the coffin corner envelope. You then only need the Thales pitot clog-up over time to create a coffin corner encounter (see theShadow's post at link http://www.pprune.org/rumours-news/3...ml#post5537109 for the outcome of that cumulative {over time} additive error). The conclusion is that a freeze-over of the TAT sensor would have put them, courtesy of the ADIRS, at a higher actual TAS. Usually the temperature isn't a factor or a consideration, except when it's a "phony" one.
.
Also, in this regard, the article claims fairly authoritatively that AF447 was heavy (i.e. cargo and pax-laden) so went early direct to best height (FL350) looking for optimum SFC (i.e. to "make" fuel and avoid any enroute drop-short of destination reserves requirements.). That in itself would have quite early put a heavy AF447 closer than normal to the upper RH edge of the operating envelope and that much closer to a Mach Crit encounter. The fact that they never reported "Level FL350" - but only read-back that final cleared height - may indicate that they levelled and soon thereafter accelerated straight into a compressibility encounter..... having already accumulated some of the icing-induced errors on climb.
____________________________________
Answer: 2. Once again depends (as theShadow points out with respect to the pitot heaters) upon the heating capacity of the sensor's protection. Having atmospheric precipitation freeze upon impact to form ice is quite a different thermal proposition in aviation to accumulating an agglomeration of already formed supercooled ice crystals over time during a relatively smooth cruise in Cirrostratus/Cirrocumulus. But in the Thales pitot head, by contrast, the tendency was to "collect" the ice crystals inside a tube and thus gradually (insidiously) clog the pneumatic flows and sensed pressures. An assumption can be made that a false high TAT (and consequent high undetected TAS), due to a thickening sensor ice-coating, was a possibility.
____________________________________
QUES: 3.
From the article: "The crew immediately recognized that the three airspeed indicators all gave different readings. "A situation like that goes well a hundred times and badly once," says Arnoux, who flies an Airbus A320 himself."
Thrice Almighty - The Virtues of Triple Redundancy | Air Safety Week | Find Articles at BNET
________________________________- Over to others who may be better informed/educated.
.
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May I remind the people that NASA used triple redundancy on the Apollo program, if no others. But they did not use three of the same computer. They used two IBM computers and one Rockwell International computer. That way if the code was bad in IBM it could still be good in the Rockwell computer, and of course the other way around holds true as well.
If the interface description is up to snuff for the computers there could and should be two different designs and a rule that both had to be in use on any given plane. And with CPUs being what they are TODAY any new design should feed all sensors to all computers through interfaces that don't fail if one of the computer input interfaces dies.
This sort of thing has been done before. NASA, if nobody else, has shown how.
I've run the failure analysis process looking for single point of failure events, I've used triple redundancy before. Specifically it is what keeps the GPS satellites on the "desired" frequency while on orbit despite Rb and Cs standard drift. And it should be noted that sometimes 'desired' is not nominal so that it's harder to plonk a missile down Jimmy Carter's toity when he was in the White House using GPS. (That was when it was initially designed and the chief reason for it. GPS accuracy enhancement is a fallout of the design.)
{o.o}
If the interface description is up to snuff for the computers there could and should be two different designs and a rule that both had to be in use on any given plane. And with CPUs being what they are TODAY any new design should feed all sensors to all computers through interfaces that don't fail if one of the computer input interfaces dies.
This sort of thing has been done before. NASA, if nobody else, has shown how.
I've run the failure analysis process looking for single point of failure events, I've used triple redundancy before. Specifically it is what keeps the GPS satellites on the "desired" frequency while on orbit despite Rb and Cs standard drift. And it should be noted that sometimes 'desired' is not nominal so that it's harder to plonk a missile down Jimmy Carter's toity when he was in the White House using GPS. (That was when it was initially designed and the chief reason for it. GPS accuracy enhancement is a fallout of the design.)
{o.o}
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This has been posted on Flightglobal, if it's of interest:
Complexity of AF447 crash probe to dominate ICAO discussion
Complexity of AF447 crash probe to dominate ICAO discussion
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JD-EE
Consider that the Auto Pilot dropped as a result of its being "unable" to control the a/c with its set of limited control commands.
Remanded to "Manual", the pilots have a serious challenge, again as the result of what I propose is the a/p's "long leash". Given that the a/c is oscillating inside an envelope of prescribed parameters, and its cruise (.82 Mach) speed, whatever caused the ap to retreat is now in the hands of a man whom we assume is at Cruise, SA-wise. A hyper-vigilant Chief Pilot would be challenged as he never had been in his life.
Now consider another possibility. The a/c was not under threat at all.
As the micro-crystalline Water Ice packs up the pitots and hobbles the OAT sensor, the a/p "reads" the flight status as dynamic, rather than static. It doesn't think, and it can't hear, so it makes inputs to "correct" what is becoming a rapidly deteriorating (to it) situation. It is likely reading slowing a/s, so lowers the nose a titch, and perhaps augments thrust, just to "smooth and speed" the "recovery". But it isn't working. It's only plan is to correct, not stop and assess. Sometimes doing nothing is better than doing something. But the autopilot soldiers on. How quickly did the limits cause the a/p to shut down? Let's hope it didn't allow the Pitch and speed to get too wack, but one thinks it did.
Energy. At a high velocity, "slowing down" takes time. The a/c is clean, and the descent devices are not available for quite awhile, they would be battered to bits. What caused this a/c to slow rapidly? If, as mm43 proposes, the a/c was in a turn and Impacted not far from its "onset" position, there are only unpleasant suppositions.
Small and sharp things leave first, wingtips, tail bits, skin that is disturbed by the departure of objects of ever increasing size, which exacerbates the deceleration and donation of parts to the air and sea below. At some point the velocity is low enough and the relative strength is high enough that a "balance" is achieved, and the airframe settles into its likely flat spin to the Sea.
Nothing about this is proposed to be certain, there is too much missing from the puzzle. It is minimally informed supposition. Guesswork.
587 lost an engine (as in separation) almost immediately, wake turbulence is a beast, low and slow. Primary failure at altitude and close to the speed of sound? Somehow (someway) 447 recovered to impact the Sea on the verge of complete recovery?? Not saying it's impossible, but....
So that is one answer to this aircraft's having been "swatted from the sky". I tend to agree that velocity was lost quickly, and disastrously.
bear
Consider that the Auto Pilot dropped as a result of its being "unable" to control the a/c with its set of limited control commands.
Remanded to "Manual", the pilots have a serious challenge, again as the result of what I propose is the a/p's "long leash". Given that the a/c is oscillating inside an envelope of prescribed parameters, and its cruise (.82 Mach) speed, whatever caused the ap to retreat is now in the hands of a man whom we assume is at Cruise, SA-wise. A hyper-vigilant Chief Pilot would be challenged as he never had been in his life.
Now consider another possibility. The a/c was not under threat at all.
As the micro-crystalline Water Ice packs up the pitots and hobbles the OAT sensor, the a/p "reads" the flight status as dynamic, rather than static. It doesn't think, and it can't hear, so it makes inputs to "correct" what is becoming a rapidly deteriorating (to it) situation. It is likely reading slowing a/s, so lowers the nose a titch, and perhaps augments thrust, just to "smooth and speed" the "recovery". But it isn't working. It's only plan is to correct, not stop and assess. Sometimes doing nothing is better than doing something. But the autopilot soldiers on. How quickly did the limits cause the a/p to shut down? Let's hope it didn't allow the Pitch and speed to get too wack, but one thinks it did.
Energy. At a high velocity, "slowing down" takes time. The a/c is clean, and the descent devices are not available for quite awhile, they would be battered to bits. What caused this a/c to slow rapidly? If, as mm43 proposes, the a/c was in a turn and Impacted not far from its "onset" position, there are only unpleasant suppositions.
Small and sharp things leave first, wingtips, tail bits, skin that is disturbed by the departure of objects of ever increasing size, which exacerbates the deceleration and donation of parts to the air and sea below. At some point the velocity is low enough and the relative strength is high enough that a "balance" is achieved, and the airframe settles into its likely flat spin to the Sea.
Nothing about this is proposed to be certain, there is too much missing from the puzzle. It is minimally informed supposition. Guesswork.
587 lost an engine (as in separation) almost immediately, wake turbulence is a beast, low and slow. Primary failure at altitude and close to the speed of sound? Somehow (someway) 447 recovered to impact the Sea on the verge of complete recovery?? Not saying it's impossible, but....
So that is one answer to this aircraft's having been "swatted from the sky". I tend to agree that velocity was lost quickly, and disastrously.
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Belgique ...
The fact that they never reported "Level FL350" - but only read-back that final cleared height - may indicate that they levelled and soon thereafter accelerated straight into a compressibility encounter..... having already accumulated some of the icing-induced errors on climb.
The fact that they never reported "Level FL350" - but only read-back that final cleared height - may indicate that they levelled and soon thereafter accelerated straight into a compressibility encounter..... having already accumulated some of the icing-induced errors on climb.
JD-EE has already dealt with the NASA approach to the subject. However, I would have to say that the tried and proven saying of "garbage in equals garbage out" is important here. If two components of the equation (pitot & temperature senors) can fail because of one cause, e.g. ice, then there needs to be an alternative means of measurement.
In respect of the FL350 level time, I am not sure exactly when they levelled, but on transfer to Recife Center at 23:19:27z (50 minutes after take off) they reported level at FL350. Curitiba Center cleared them to FL350 at 22:55:41z and it would be interesting to know from what level, and the time they actually levelled. This means that they had been at FL350 for at least 2 hours 50 minutes prior to the upset.
mm43
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Redundancy, or replication, is of less use in critical systems than parallel but anomalous systems. BA038 satisfied all ETOPS requirements, but in hind sight and to this day, critical systems tend to replicate each other as the destination of each system is approached, rather than continue to supply, meter, or control critical systems in independently engineered ways.
Taken to an extreme, BA 038 could have been fitted with separate but similar powerplants, ie. one GE and one Trent. As silly as it sounds, it represents what I feel is a neglected discipline.
Redundancy depends on reliability, and as we know, in Aviation, reliability is a frequently "balanced" consideration.
If one device has a freckle, two more will also. In 2003, Thales researched and recommended a separate sensing system for airspeed.
mm43
As the RTLU was found in its Normal Law setting, what is the implication regarding travel? Was the Rudder free to travel stop to stop, was it pinned in a centered position? Etc. I am extremely impressed with your contributions to this thread. What of the initial reports that bodies were recovered in "two separate areas, separated by fifty miles?" What do you make of the found positions re: VS, Galley, wing bits, aileron, Elevator, Spoiler, et al?
bear
Taken to an extreme, BA 038 could have been fitted with separate but similar powerplants, ie. one GE and one Trent. As silly as it sounds, it represents what I feel is a neglected discipline.
Redundancy depends on reliability, and as we know, in Aviation, reliability is a frequently "balanced" consideration.
If one device has a freckle, two more will also. In 2003, Thales researched and recommended a separate sensing system for airspeed.
mm43
As the RTLU was found in its Normal Law setting, what is the implication regarding travel? Was the Rudder free to travel stop to stop, was it pinned in a centered position? Etc. I am extremely impressed with your contributions to this thread. What of the initial reports that bodies were recovered in "two separate areas, separated by fifty miles?" What do you make of the found positions re: VS, Galley, wing bits, aileron, Elevator, Spoiler, et al?
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Bearfoil
Once the maximum allowable rudder angle is computed, the RTLU stop screw turns incrementally to implement the angle.
Much of the information released by the Brazilian Military was designed for media consumption and on analysis was mostly devoid of "facts". A series of debris charts released by the BEA and showing where and when various (but undisclosed as to what component) items were recovered, also shows positions for the bodies. It should be pointed out that due to the 36g force they suffered on impact, and other events that happen in the sea, most of those bodies will not have behaved as one would expect.
I have no further information to identify specific items of debris, other than that provided graphically by the BEA for the V/S, and for the Port Outer Spoiler obtained from a very reliable source. The difficulty with back-tracking the various objects is determining how they actually behaved in different sea states and wind. This is why the phase 3 search area is still relatively large, ie. 887NM2.
Perhaps the scenario you are developing fits the following, though substitute the "mountain wave" for a severe mesoscale event:-
In AF447's case, ACARS was quite capable of providing some clues to any of those events, but it didn't, and may be because they didn't happen.
mm43
As the RTLU was found in its Normal Law setting, what is the implication regarding travel? Was the Rudder free to travel stop to stop, was it pinned in a centered position?
What of the initial reports that bodies were recovered in "two separate areas, separated by fifty miles?"
What do you make of the found positions re: VS, Galley, wing bits, aileron, Elevator, Spoiler, et al?
Perhaps the scenario you are developing fits the following, though substitute the "mountain wave" for a severe mesoscale event:-
On March 5, 1966, British Overseas Airways flight 911, a Boeing 707, departed Tokyo for Hong Kong with 124 people and the cabin crew aboard. Because of the clear weather at the time, the pilot asked for and received an amendment to the scheduled flight plan that would allow his passengers an up-close view of Mt. Fuji. Shortly after the airplane began its descent toward the mountain, witnesses reported seeing the airplane trailing white vapor and shedding pieces. The witnesses also reported that they saw a large puff of vapor that came from the airplane’s vertical stabilizer and that the airplane pitched up and entered a flat spin. The witnesses further reported that the vertical stabilizer assembly and engines were missing, the outer wing had failed, the forward fuselage broke off, and the airplane continued in a flat spin until it crashed into the base of Mt. Fuji. All of the airplane occupants were killed. The report on this accident indicated that, when approaching Mt. Fuji, the airplane was violently impacted by a severe mountain wave, which led to vertical stabilizer failure and subsequent in-flight breakup. (A U.S. Navy aircraft, which was dispatched to search for the flight 911 wreckage, encountered extreme turbulence near the area of the crash. In fact, the G meter installed on the U.S. Navy aircraft registered +9 to -4 Gs during the flight.) The report also identified the white vapor as jet fuel flowing out of the airplane after separation of the engines.
mm43
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Bearfoil, one correction: I believe I was the one proposing the possible turn based on mm43's data. I didn't mean to impute something to mm43 he might not have said.
And my understanding is that once the speed indications differ the computers go off-line suddenly while the plane is likely in very heavy turbulence.
Something else came to mind. I'm not a pilot so this needs feedback from a real pilot. If something caused an engine stall, which could account for loss of ACARS transmissions, the pilots would not be concerned about compass heading so much as aligning the plane nose down to gain speed to restart the engines. This could have lead to the mysterious heading change. Then the desperate attempt to pull out as the ocean came into view might finish the scenario, engines started or not.
{^_^}
And my understanding is that once the speed indications differ the computers go off-line suddenly while the plane is likely in very heavy turbulence.
Something else came to mind. I'm not a pilot so this needs feedback from a real pilot. If something caused an engine stall, which could account for loss of ACARS transmissions, the pilots would not be concerned about compass heading so much as aligning the plane nose down to gain speed to restart the engines. This could have lead to the mysterious heading change. Then the desperate attempt to pull out as the ocean came into view might finish the scenario, engines started or not.
{^_^}
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I think our crew are well challenged w/o loss of an engine. It hasn't been discussed much, but it did appear. Crap airdata is certainly enough, we're starting to sound like a sim instructor throwing the sink at a pilot who's dating his wife.
We could disregard all the initial buzz about "breaking up in the air," "autopsies prove plane broke up". "no water in lungs...." etc.
If the accel value is said to be 36 g, well, the belts are stressed to forty, and w/o harness, not survivable.....just. Some victims would have water in their lungs, yet none did. Turbulence isn't a conclusion, it could have been as simple as a pint glass full of crystalline water ice. Not enough for two margaritas. God Bless them all.
We could disregard all the initial buzz about "breaking up in the air," "autopsies prove plane broke up". "no water in lungs...." etc.
If the accel value is said to be 36 g, well, the belts are stressed to forty, and w/o harness, not survivable.....just. Some victims would have water in their lungs, yet none did. Turbulence isn't a conclusion, it could have been as simple as a pint glass full of crystalline water ice. Not enough for two margaritas. God Bless them all.
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mm43,
I was just riffing in email with SallyAnne on my idea of sending delta positions as part of every ACARS message. If I remember correctly there is a full position report every 10 minutes. Planes seldom cover more than 50 miles from their last position report until the next one. Figure that as one BYTE of information each for latitude and longitude delta. At 0.2 miles resolution that's about a four orders of magnitude reduction in position possibilities in 10 minutes. Imagine the affect this would have on the search operations. It's a change to ACARS messages that would probably pay for itself in savings from one over the ocean disaster. Even the recent event West of Lebanon would have been easier for recovery.
(You's even be able to get a useful improvement in a pair of 64 bit printable characters using "Base64" style encoding and working with deltas from last delta or last position report extrapolated with its velocity vector.)
Relative to new fancier recorders or full time data streams this would be a really cheap solution with a large potential payback.
{^_^}
I have no further information to identify specific items of debris, other than that provided graphically by the BEA for the V/S, and for the Port Outer Spoiler obtained from a very reliable source. The difficulty with back-tracking the various objects is determining how they actually behaved in different sea states and wind. This is why the phase 3 search area is still relatively large, ie. 887NM2.
(You's even be able to get a useful improvement in a pair of 64 bit printable characters using "Base64" style encoding and working with deltas from last delta or last position report extrapolated with its velocity vector.)
Relative to new fancier recorders or full time data streams this would be a really cheap solution with a large potential payback.
{^_^}
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{mumble}{mumble}
Just when did this engine break away, bearfoil? And where does word of this mildly dramatic event appear in the ACARS reports? I'd even hazard a guess that something as dramatic as a VS separation would also be quite evident in the ACARS messages if it happened at altitude.
It takes a minute or to for something plane shaped to make a 35,000' altitude change unless it's in a vertical dive. And that would chop off ACARS messages. (A dive more than maybe 30 degrees in the right direction would block ACARS. In the likely direction it'd take closer to 45 degrees, I suspect. The ACARS antenna has a rather broad beam width judging from its specified gain.)
So it appears ACARS was unaware of really dramatic events such as significant pieces leaving the plane. (And if the plane was at altitude for that last report, belied by cabin pressure warnings, the debris was in the wrong place.)
{^_^}
Just when did this engine break away, bearfoil? And where does word of this mildly dramatic event appear in the ACARS reports? I'd even hazard a guess that something as dramatic as a VS separation would also be quite evident in the ACARS messages if it happened at altitude.
It takes a minute or to for something plane shaped to make a 35,000' altitude change unless it's in a vertical dive. And that would chop off ACARS messages. (A dive more than maybe 30 degrees in the right direction would block ACARS. In the likely direction it'd take closer to 45 degrees, I suspect. The ACARS antenna has a rather broad beam width judging from its specified gain.)
So it appears ACARS was unaware of really dramatic events such as significant pieces leaving the plane. (And if the plane was at altitude for that last report, belied by cabin pressure warnings, the debris was in the wrong place.)
{^_^}