AF 447 Search to resume
Per Ardua ad Astraeus
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In true 'wet blanket' mode, I am minded to quote (from Wikipedia) from William Chillingworth's Religion of Protestants.[5], where he accuses unnamed scholastics of debating " Whether a Million of Angels may not fit upon a needles point?"
Much as I am in awe of mm's invaluable contributions elsewhere on this thread, I cannot believe we are down to surmising how many g (to one decimal point indeed) were experienced at impact. Only those who have had 'hands on' those bits of metal and plastic, and, sadly bodies, will have a 'feel' for what happened. High speed wing down/bottoming out, ripping the fin off at high forward g (causing the belt injuries), low speed vertical, flat spin - all supposition. Indeed, despite the language issues, the deceleration COULD have even been 36g as well as the part number! It is all very interesting and extremely clever but it doesn't really move anything forward. Far more important is to identify what went wrong at cruise altitude, examine the software interactions involved and correct any deficiencies. If/when more bits/recorders are located we move on to the detail of the impact. This really should be the thrust of this thread - in my opinion.
Maybe a thread split (mods?) is called for so we can focus more clearly on the progress of the search (as per title) as opposed to hypotheses on just one part of the accident.
Much as I am in awe of mm's invaluable contributions elsewhere on this thread, I cannot believe we are down to surmising how many g (to one decimal point indeed) were experienced at impact. Only those who have had 'hands on' those bits of metal and plastic, and, sadly bodies, will have a 'feel' for what happened. High speed wing down/bottoming out, ripping the fin off at high forward g (causing the belt injuries), low speed vertical, flat spin - all supposition. Indeed, despite the language issues, the deceleration COULD have even been 36g as well as the part number! It is all very interesting and extremely clever but it doesn't really move anything forward. Far more important is to identify what went wrong at cruise altitude, examine the software interactions involved and correct any deficiencies. If/when more bits/recorders are located we move on to the detail of the impact. This really should be the thrust of this thread - in my opinion.
Maybe a thread split (mods?) is called for so we can focus more clearly on the progress of the search (as per title) as opposed to hypotheses on just one part of the accident.
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36g, continued
RE: Diversification #471 - 36g again
I respectfully submit that we have two translations - one with the linguístic and engineering expertise of the BEA behind it, and one from "a person born in the UK, educated both there and in France, and who has lived in France for over 40 years".
The latter may well be linguistically correct, but in my opinion it does not reflect what the BEA is trying to say. In my opinion the word "corresponding to" is intended to link "120 000 N" to another quantity, e.g. "36 g", and not just an arm.
Edit:
Its turns out that my first calculation was too simplistic and it has therefore been deleted. The FAR Part 25 regulations specify an ultimate load corresponding to 24*1.5=36 g. The rudder and supporting hinge brackets must be able to support an inertia ultimate load acting parallel to the hinge line of 24*1.5=36 times the weight of the rudder. Since Arm 36g is at an angle of 38 degrees to the rudder hinge line, 120 000 N in the direction of that arm corresponds to 94 561 N along the rudder hingeline, and hence to a rudder mass of 268 kg.
regards,
HN39
The correct translation (see post #440) of the french report shows that 36 g is a part name and not acceleration.
The latter may well be linguistically correct, but in my opinion it does not reflect what the BEA is trying to say. In my opinion the word "corresponding to" is intended to link "120 000 N" to another quantity, e.g. "36 g", and not just an arm.
Edit:
Its turns out that my first calculation was too simplistic and it has therefore been deleted. The FAR Part 25 regulations specify an ultimate load corresponding to 24*1.5=36 g. The rudder and supporting hinge brackets must be able to support an inertia ultimate load acting parallel to the hinge line of 24*1.5=36 times the weight of the rudder. Since Arm 36g is at an angle of 38 degrees to the rudder hinge line, 120 000 N in the direction of that arm corresponds to 94 561 N along the rudder hingeline, and hence to a rudder mass of 268 kg.
regards,
HN39
Last edited by HazelNuts39; 14th Mar 2010 at 17:10. Reason: revised calculation of rudder mass
36g
I wouldn't expect an engineering report to be concerned with the equivalent acceleration. UTS and/or breaking force yes as this would be directly available from the design intent and FE models. That's why I bought in to '36g' not being an acceleration.
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36 g
Hazelnut.
I will try to explain and motivate my opinion. When I/you look carefully at the photo where the corroded edge of "arm 36 g" and the bolt is shown it is rather obvious that there was no movement between these. Any such movement would have been stretching of the arm and would have lead to scratching and deformation of the "lock" substance still surrounding the six-edged bolt head. My very personal opinion is that what we can see from the picture is a corrosion damage to the arm. Possibly induced by the tension caused by the bolt. I have seen very similar corrosion phenomena on some older outboard engines.
I will try to explain and motivate my opinion. When I/you look carefully at the photo where the corroded edge of "arm 36 g" and the bolt is shown it is rather obvious that there was no movement between these. Any such movement would have been stretching of the arm and would have lead to scratching and deformation of the "lock" substance still surrounding the six-edged bolt head. My very personal opinion is that what we can see from the picture is a corrosion damage to the arm. Possibly induced by the tension caused by the bolt. I have seen very similar corrosion phenomena on some older outboard engines.
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PJ2
I have a few questions.
At "unreliable airspeed" and a/p disconnect, was the a/c experiencing attitudes/control inputs that had exceeded the autopilots programmed range? Or did the a/p decouple simply because of uA/S?
Other a/c had encountered unreliable a/s, without turbulences forte, could 447 have been in still air? How quickly did the a/c revert to Alternate Law II, then Direct?
Could the pilots have been so quickly left with an a/c needing manual control only that they overcontrolled into upset?
RTLU. Is travel limited by mechanical (dynamic) stops? Or is it restricted by pressure/sensing of hydraulics?
At 4/8total sweep, (degrees) and mechanical stops, without hydraulics diminished, can the Rudder experience rapid reversals and subject the a/c to cycling divergent Yaw?
ACARS cadence. Could the a/c have remained under control through all ACARS, and at altitude?
Cabin. Could the Cabin Pressure FAIL transmission have been an auto alert that pressurization was lost, at altitude?
On mm43's excellent "debris" graphic, isn't the Vertical Stabiliser/Rudder shown at the "Start" of the field? The Spoiler well "past" it?
Had the a/c 'disintegrated' (this is a very loose term, meaning lost parts at altitude), wouldn't the debris field be expected to be compact? Would it not also indicate a quite "rapid" descent to the Sea, explaining the proximity of the debris on the surface to 447's last "reported position"?
bear
I have a few questions.
At "unreliable airspeed" and a/p disconnect, was the a/c experiencing attitudes/control inputs that had exceeded the autopilots programmed range? Or did the a/p decouple simply because of uA/S?
Other a/c had encountered unreliable a/s, without turbulences forte, could 447 have been in still air? How quickly did the a/c revert to Alternate Law II, then Direct?
Could the pilots have been so quickly left with an a/c needing manual control only that they overcontrolled into upset?
RTLU. Is travel limited by mechanical (dynamic) stops? Or is it restricted by pressure/sensing of hydraulics?
At 4/8total sweep, (degrees) and mechanical stops, without hydraulics diminished, can the Rudder experience rapid reversals and subject the a/c to cycling divergent Yaw?
ACARS cadence. Could the a/c have remained under control through all ACARS, and at altitude?
Cabin. Could the Cabin Pressure FAIL transmission have been an auto alert that pressurization was lost, at altitude?
On mm43's excellent "debris" graphic, isn't the Vertical Stabiliser/Rudder shown at the "Start" of the field? The Spoiler well "past" it?
Had the a/c 'disintegrated' (this is a very loose term, meaning lost parts at altitude), wouldn't the debris field be expected to be compact? Would it not also indicate a quite "rapid" descent to the Sea, explaining the proximity of the debris on the surface to 447's last "reported position"?
bear
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"arm 36 g" corrosion
RE: Diversification #471
I am hesitating to respond to your opinion because, as you said in your post #449, this has probably little to do with the cause of the accident and even less with the search.
I have carefully looked at the photo, but my untrained eyes don't see what you see. I would think that, if "arm 36 g" had been substantially weakened by corrosion, that fact would have been much more evident to the experts examining the vertical tail structure, and BEA would not only have mentioned that finding in their report, but would have called for an immediate inspection of that part on all A330/A340's.
Regards,
HN39
I am hesitating to respond to your opinion because, as you said in your post #449, this has probably little to do with the cause of the accident and even less with the search.
I have carefully looked at the photo, but my untrained eyes don't see what you see. I would think that, if "arm 36 g" had been substantially weakened by corrosion, that fact would have been much more evident to the experts examining the vertical tail structure, and BEA would not only have mentioned that finding in their report, but would have called for an immediate inspection of that part on all A330/A340's.
Regards,
HN39
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I think what Diversification is suggesting has merit. Vertical Load attenuation by Arm 36 (g) is accomplished by "snubbing" tension between the Pivot Sheath and the Vertical Aft Spar (not seen) in the Vertical Stabiliser. The "Lobe" (tip) of the Arm is missing. It has escaped from underneath the shoulder of the "thru-bolt" securing (both) VA assemblies.
It has done this without evidence that the Bolt's seat upon the remainder of the starboard ARM has been disturbed (by observation). To do this, the tip will have had to have been loaded by the Bolt, whose appearance disavows any lateral movement. An alternate explanation would be perhaps that the Rudder was exposed to Load, and thence severe vibration, such that the tip was ejected by the remaining mount structure (Barrel, Bolt, Arm), under stress. This would suggest the Arm had been degraded in some way, weakening the attachment at the lobe. Corrosion would be an obvious precursor.
Further, consonant with vibration of the Rudder, an alternate compression as a partner to the loss of the Arm tip. Vibration? Not unusual, but without degradation of the Arm's tip, it will have had to have been a result of severe and un-engineered for (catastrophic) stress. Flutter comes to mind, or rapid cycling control inputs, either pilot induced or a/p.
This (potential) vibration would go some way to explain the loss of skin and ribs at the base of the Rudder. Aerodynamic in nature rather than impact related. It would also account for the undisturbed hinges and their mounting. These "plates", each a pair bracketing the Rudders pivot, are not seen to be deformed, again suggesting that though a part of the Vertical was destroyed in Tension, there was insufficient "stretching" of the Pivot. One would expect a deformation downward in these plates, had there been enough movement in the vertical to fail the end of the ARM, absent the vibration or some other as yet not explained loading.
bear
It has done this without evidence that the Bolt's seat upon the remainder of the starboard ARM has been disturbed (by observation). To do this, the tip will have had to have been loaded by the Bolt, whose appearance disavows any lateral movement. An alternate explanation would be perhaps that the Rudder was exposed to Load, and thence severe vibration, such that the tip was ejected by the remaining mount structure (Barrel, Bolt, Arm), under stress. This would suggest the Arm had been degraded in some way, weakening the attachment at the lobe. Corrosion would be an obvious precursor.
Further, consonant with vibration of the Rudder, an alternate compression as a partner to the loss of the Arm tip. Vibration? Not unusual, but without degradation of the Arm's tip, it will have had to have been a result of severe and un-engineered for (catastrophic) stress. Flutter comes to mind, or rapid cycling control inputs, either pilot induced or a/p.
This (potential) vibration would go some way to explain the loss of skin and ribs at the base of the Rudder. Aerodynamic in nature rather than impact related. It would also account for the undisturbed hinges and their mounting. These "plates", each a pair bracketing the Rudders pivot, are not seen to be deformed, again suggesting that though a part of the Vertical was destroyed in Tension, there was insufficient "stretching" of the Pivot. One would expect a deformation downward in these plates, had there been enough movement in the vertical to fail the end of the ARM, absent the vibration or some other as yet not explained loading.
bear
Last edited by bearfoil; 13th Mar 2010 at 18:00.
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BOAC ...
"Whether a Million of Angels may not fit upon a needles point?" by William Chillingworth
"Whether a Million of Angels may not fit upon a needles point?" by William Chillingworth
BOAC, your point is taken regarding the name of the thread, but I note that there's no comment on the BEA's "Search delayed" news release. Are we all waiting with baited breath for the substantive update on Monday?
Just a minor point regarding the Interim Report No.2 translation - a careful read of a few paragraphs and sentences in and around the 'Arm 36 g' location will reveal that possibly three persons have had a hand in the result. The literal translation of "dérive" has resulted in "fin", "vertical stabiliser" and "vertical stabilizer". They are all correct. So wonder not, when the "de 36 g de" business gets raised, along with the staple "en ligne de vol".
Answers to the cause, rather than the result is what is truly needed, and there will always be a case for determining what could have been done in the intervening period. In the meantime, "Idle Minds" will play with 36g, the vertical stabilizer and belly flops.
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Search to resume 25 March 2010 -
The following is a Reuters India report quoting Le Figaro -
Air France black box search to resume on Mar.25 - paper | World | Reuters
The BEA's press release on Monday may not be so speculative.
mm43
Air France black box search to resume on Mar.25 - paper | World | Reuters
The BEA's press release on Monday may not be so speculative.
mm43
bearfoil, your questions in black font, my thoughts in blue:
At "unreliable airspeed" and a/p disconnect, was the a/c experiencing attitudes/control inputs that had exceeded the autopilots programmed range? Or did the a/p decouple simply because of uA/S?
The autopilot will disconnect if the pitch attitude exceeds 25deg NU, 13degND or 45deg Roll. I believe the AF330 in question was equipped with EGPWS which in some installations will have a "Bank Angle" warning. I would expect at some point that an ECAM message to be generated but we dont' have enough information to make this assumption. For further, the BEA 2nd Interim Report,
Other a/c had encountered unreliable a/s, without turbulences forte, could 447 have been in still air? How quickly did the a/c revert to Alternate Law II, then Direct?
Assumptions made that the a/c was in turbulence would come from the many weather and satellite images available and the most-likely track information provided by many very skilled posters.
Such conclusions may even be reasonable but there is nothing to directly indicate or necessarily conclude that the a/c was in turbulent air or convective weather.
None of us (I assume) has actually examined the wreckage first-hand and with sufficient engineering knowledge come to conclusions which are substantially at odds with the BEA statements regarding the likely trajectory and attitude of the aircraft.
This is not stating that the BEA conclusions are necessarily what happened but a lot of people who kick tin and who can "read" metal have not put forward theories explaining the evidence from the wreckage which supports contrary theories. Many I'm sure would be very interested in serious theories based upon alternate interpretations of the traces in the metal and the cabin material which support for example, mid-air loss of the VS.
One possibility we might anticipate when the recorders are found and read is the loss of data after the loss of control. The recorders are powered off the AC1, AC2 and DC2 busses. I have long theorized that once LOC occurred and the descent established, due to extreme angles of airflow across the engine inlets upsetting the flow through the engines that the possibility exists that they may have flamed out at . Loss of the AC1 and AC2 busses would deploy the RAT for hydraulics and the AC and DC Essential busses, (again, no recorders powered) but again very high angles of airflow relative to the longitudinal axis/chord of the aircraft would preclude its use; if the RAT is the only source of power, load-shedding begins if the CAS is < 260kts. Whether the APU would start in such circumstances, (using APU-dedicated battery) and whether that occurred is also cannot be known.
Could the pilots have been so quickly left with an a/c needing manual control only that they overcontrolled into upset?
Highly speculative when involving human and environmental factors but in what may have been more benign circumstances we have thirteen other examples of loss of ADR data due loss of pitot information in which no loss of control occurred. We cant' conclude that no loss of control would occur as a result of a sudden requirement for manual flight. I can't see experiened pilots "over-controlling" the airplane into a loss-of-control merely from loss of airspeed information, (fly pitch, bring the thrust levers back out of the CLB detent and set the N1 that was being used before the problem, get the checklist out), but that said, we have also seen a number of industry events in which wild excursions occurred as a result of untoward pilot input so we know it can occur.
RTLU. Is travel limited by mechanical (dynamic) stops? Or is it restricted by pressure/sensing of hydraulics?
Rudder travel is limited in two ways both of which are mechanical: the PTLU and RTLU are similar in structure. According to a schematic, they are co-located in the VS, the RTLU about 1/2 the way up the VS, the PTLU at the base of the VS where the rudder and VS structure join. From the BEA 2nd Interim Report:
"1.12.3.5.5 Examination of the Rudder Travel Limiter Unit (RTLU)
At 4/8total sweep, (degrees) and mechanical stops, without hydraulics diminished, can the Rudder experience rapid reversals and subject the a/c to cycling divergent Yaw?
I'm not qualified to say it isn't possible from a design or engineering pov. I have done in the past a survey but not an exhaustive study of Advsories and Directives on other matters and there was not a reference to such an issue or event. To my awareness there is no known occurrence of uncommanded rudder reversal or rapid reversal movements recorded or discussed in any Airbus literature/incident/safety reporting system I have seen or have access to and have studied nor have I experienced it in any aircraft.
The BEA Report indicates that the RTLU permitted a rudder travel of 7.9deg.
ACARS cadence. Could the a/c have remained under control through all ACARS, and at altitude?
There are important understandings about the ACARS messages one of which I stated very early in the first AF447 thread which was eventually closed, and which was clearly stated in the 1rst Interim Report. That comment was, "It is therefore possible in a CFR to find an ECAM message preceding a fault message that is nevertheless timed one minute before it." So the assumption that the ACARS messages are in some meaningful order from which possible cause may be derived, is incorrect. Rather, the need for examining what caused within each affected system a ECAM Class 2 message to trigger as well as understanding what the protocols of that system to send the notice-of-failure to the CMC and for the CMC to prioritize the message and send it thence to the ACARS, must be appreciated.
I do not see direct evidence in any of the ACARS messages that the a/c was out of control. The "Advisory Cabin Vertical Speed" has been cited as one indication of loss of pressurization but the conditions are a rate < or > 1800fpm as compared
Cabin. Could the Cabin Pressure FAIL transmission have been an auto alert that pressurization was lost, at altitude?
As described in the previous response, although it is possible we cannot conclude this. There are a number of interpretations from the FCOM; the AMM does not do a good job of covering Advisory messages. Essentially, the FCOM actions required for this message are to switch CPC's...Cabin Pressure Controllers. Control is switched to MANual then back to AUTO which changes the CPC's. Although one would believe the 1800fpm rates to be those actually sensed, I can imagine at least one interpretation where that is the rate commanded by a CPC and a switch to the other CPC is required. Digging this deeply in the corners for any hint that the cabin itself was structurally compromised is at best a tenuous endeavour.
I hope this is somewhat helpful. I think re-reading the BEA first and second interim reports is well worth while.
PJ2
At "unreliable airspeed" and a/p disconnect, was the a/c experiencing attitudes/control inputs that had exceeded the autopilots programmed range? Or did the a/p decouple simply because of uA/S?
The autopilot will disconnect if the pitch attitude exceeds 25deg NU, 13degND or 45deg Roll. I believe the AF330 in question was equipped with EGPWS which in some installations will have a "Bank Angle" warning. I would expect at some point that an ECAM message to be generated but we dont' have enough information to make this assumption. For further, the BEA 2nd Interim Report,
"1.16.3 Study of losses of or temporary anomalies in indicated speeds occurring in cruise on Airbus A330 / A340", can be referenced. The autopilot and autothrust disconnected in ten of the thirteen recorded cases of this series of events.
Other a/c had encountered unreliable a/s, without turbulences forte, could 447 have been in still air? How quickly did the a/c revert to Alternate Law II, then Direct?
Assumptions made that the a/c was in turbulence would come from the many weather and satellite images available and the most-likely track information provided by many very skilled posters.
Such conclusions may even be reasonable but there is nothing to directly indicate or necessarily conclude that the a/c was in turbulent air or convective weather.
None of us (I assume) has actually examined the wreckage first-hand and with sufficient engineering knowledge come to conclusions which are substantially at odds with the BEA statements regarding the likely trajectory and attitude of the aircraft.
This is not stating that the BEA conclusions are necessarily what happened but a lot of people who kick tin and who can "read" metal have not put forward theories explaining the evidence from the wreckage which supports contrary theories. Many I'm sure would be very interested in serious theories based upon alternate interpretations of the traces in the metal and the cabin material which support for example, mid-air loss of the VS.
One possibility we might anticipate when the recorders are found and read is the loss of data after the loss of control. The recorders are powered off the AC1, AC2 and DC2 busses. I have long theorized that once LOC occurred and the descent established, due to extreme angles of airflow across the engine inlets upsetting the flow through the engines that the possibility exists that they may have flamed out at . Loss of the AC1 and AC2 busses would deploy the RAT for hydraulics and the AC and DC Essential busses, (again, no recorders powered) but again very high angles of airflow relative to the longitudinal axis/chord of the aircraft would preclude its use; if the RAT is the only source of power, load-shedding begins if the CAS is < 260kts. Whether the APU would start in such circumstances, (using APU-dedicated battery) and whether that occurred is also cannot be known.
Could the pilots have been so quickly left with an a/c needing manual control only that they overcontrolled into upset?
Highly speculative when involving human and environmental factors but in what may have been more benign circumstances we have thirteen other examples of loss of ADR data due loss of pitot information in which no loss of control occurred. We cant' conclude that no loss of control would occur as a result of a sudden requirement for manual flight. I can't see experiened pilots "over-controlling" the airplane into a loss-of-control merely from loss of airspeed information, (fly pitch, bring the thrust levers back out of the CLB detent and set the N1 that was being used before the problem, get the checklist out), but that said, we have also seen a number of industry events in which wild excursions occurred as a result of untoward pilot input so we know it can occur.
RTLU. Is travel limited by mechanical (dynamic) stops? Or is it restricted by pressure/sensing of hydraulics?
Rudder travel is limited in two ways both of which are mechanical: the PTLU and RTLU are similar in structure. According to a schematic, they are co-located in the VS, the RTLU about 1/2 the way up the VS, the PTLU at the base of the VS where the rudder and VS structure join. From the BEA 2nd Interim Report:
"1.12.3.5.5 Examination of the Rudder Travel Limiter Unit (RTLU)
The RTLU was found in its place in the fin and disassembled. An examination
was performed at the manufacturer’s and showed that it would allow travel
of the rudder measured as 7.9° +/- 0.1°. As an example, at FL350, this travel is
obtained for Mach 0.8 +/- 0.004, corresponding to a CAS of 272 +/- 2 kt."was performed at the manufacturer’s and showed that it would allow travel
of the rudder measured as 7.9° +/- 0.1°. As an example, at FL350, this travel is
At 4/8total sweep, (degrees) and mechanical stops, without hydraulics diminished, can the Rudder experience rapid reversals and subject the a/c to cycling divergent Yaw?
I'm not qualified to say it isn't possible from a design or engineering pov. I have done in the past a survey but not an exhaustive study of Advsories and Directives on other matters and there was not a reference to such an issue or event. To my awareness there is no known occurrence of uncommanded rudder reversal or rapid reversal movements recorded or discussed in any Airbus literature/incident/safety reporting system I have seen or have access to and have studied nor have I experienced it in any aircraft.
The BEA Report indicates that the RTLU permitted a rudder travel of 7.9deg.
ACARS cadence. Could the a/c have remained under control through all ACARS, and at altitude?
There are important understandings about the ACARS messages one of which I stated very early in the first AF447 thread which was eventually closed, and which was clearly stated in the 1rst Interim Report. That comment was, "It is therefore possible in a CFR to find an ECAM message preceding a fault message that is nevertheless timed one minute before it." So the assumption that the ACARS messages are in some meaningful order from which possible cause may be derived, is incorrect. Rather, the need for examining what caused within each affected system a ECAM Class 2 message to trigger as well as understanding what the protocols of that system to send the notice-of-failure to the CMC and for the CMC to prioritize the message and send it thence to the ACARS, must be appreciated.
I do not see direct evidence in any of the ACARS messages that the a/c was out of control. The "Advisory Cabin Vertical Speed" has been cited as one indication of loss of pressurization but the conditions are a rate < or > 1800fpm as compared
Cabin. Could the Cabin Pressure FAIL transmission have been an auto alert that pressurization was lost, at altitude?
As described in the previous response, although it is possible we cannot conclude this. There are a number of interpretations from the FCOM; the AMM does not do a good job of covering Advisory messages. Essentially, the FCOM actions required for this message are to switch CPC's...Cabin Pressure Controllers. Control is switched to MANual then back to AUTO which changes the CPC's. Although one would believe the 1800fpm rates to be those actually sensed, I can imagine at least one interpretation where that is the rate commanded by a CPC and a switch to the other CPC is required. Digging this deeply in the corners for any hint that the cabin itself was structurally compromised is at best a tenuous endeavour.
I hope this is somewhat helpful. I think re-reading the BEA first and second interim reports is well worth while.
PJ2
Last edited by PJ2; 14th Mar 2010 at 08:07.
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Bearfoil
The Vertical Stabilizer was recovered from 3°36.7N 30°37.1W at around 1400z on 7 June 2009. The position has been extracted from graphics data published by the BEA. The following graphic shows my backtrack from there using Oscar/NOAA satellite smoothed current data and Quikscat satellite surface (+10m) wind data to a possible impact position of 3°12.3'N 30°54.1W at 20090601-0230z. The V/S was found floating on its port side with a small sail of torn off empennage skin attached at the forward end.
The relative position of the V/S to a body found on 6 June and another 5 found on 7 June 2009 is shown below. The calculated position for the V/S after the leeway vector has been removed is also shown. My considered opinion is that though the bodies in general suffered some windage, it wasn't evident immediately as they initially sunk to an equilibrium depth and slowly surfaced. Another reason why they were not located sooner.
The Port Outer Spoiler was found NxE of TASIL 6 days later and recovered from 04°42.1'N 029°55.6'W at 20090613-1321UTC. The assumed reason for it being north and east of most other recovered debris was that it floated flush with the surface and was well anchored in the water by the attached framing on its underside. Leeway due to surface wind has not been an issue with it.
The presumed location of this accident was effectively at the center of the doldrums and the surface currents were flowing slowly NE and turning left near 3°30N and increasing in velocity from that point. The spoiler appears to have missed the turn and like some other debris continued on towards and past TASIL to join the North Atlantic Equatorial Counter Current.
mm43
On mm43's excellent "debris" graphic, isn't the Vertical Stabiliser/Rudder shown at the "Start" of the field? The Spoiler well "past" it?
The relative position of the V/S to a body found on 6 June and another 5 found on 7 June 2009 is shown below. The calculated position for the V/S after the leeway vector has been removed is also shown. My considered opinion is that though the bodies in general suffered some windage, it wasn't evident immediately as they initially sunk to an equilibrium depth and slowly surfaced. Another reason why they were not located sooner.
The Port Outer Spoiler was found NxE of TASIL 6 days later and recovered from 04°42.1'N 029°55.6'W at 20090613-1321UTC. The assumed reason for it being north and east of most other recovered debris was that it floated flush with the surface and was well anchored in the water by the attached framing on its underside. Leeway due to surface wind has not been an issue with it.
The presumed location of this accident was effectively at the center of the doldrums and the surface currents were flowing slowly NE and turning left near 3°30N and increasing in velocity from that point. The spoiler appears to have missed the turn and like some other debris continued on towards and past TASIL to join the North Atlantic Equatorial Counter Current.
mm43
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From the pictures I've seen of the AF447 wreckage, I don't think anything from around the THS has been found that would indicate its trimmed position. I'm betting it was trimmed full nose up. Machinbird
If you're betting on that, then what is behind your assumption?
mm43
mm43
Thank you for the lead in.
When an aircraft crashes in a deep stall, it is reasonable to assume that it was also in a deep stall at higher altitudes, and that it transitioned to this condition at still higher altitudes.
Agreed, there are a number of ways to transition an airliner into a stall, but in general, more dynamic stall entries leave residual inertial moments on the airframe and work against developing a stable stall. It appears that AF447 hit the water in a stable stall configuration.
I have been looking at scenarios where an A330 could decelerate into a stall while maintaining normal attitudes. The Perpignan accident involving A320 D-AXLA, although a different Airbus model, indicated to me the amount of pitch authority Airbus builds into their THS designs and how an aircraft could be left with full nose up trim and only the manual trim wheel available to reduce this trim. When added to a triple pitot tube freeze up, and a full trim tank, the resulting cockpit “pinball show” could easily confuse an unsuspecting aircrew until it was too late. I also suspect cockpit design made it too hard to get the critical information needed (actual power setting, THS position, actual angle of attack) and as a result, the aircrew was unable to develop the big picture of what was happening. I also suspect that the A-330 can be held in a deep stall by full nose up trim and an aft CG and yet be stabilized in a relatively stable normal flight attitude by the flight control system.
Admitted, these are a lot of unproven suspicions at this point but none particularly illogical.
Consider these paragraphs from David P Davies book, “Handling The Big Jets”. Mr. Davies was Chief Test Pilot for the Air Registration Board and carried out certification testing of a large number of jet transport aircraft.
From the section on “ The Super Stall” commencing on the bottom of page 120 in my second edition copy, bold print is my emphasis, italics, the author’s. (The previous paragraphs explained why swept wing aircraft tend to pitch up after a stall.)
“Having explained the elements of the deep-stall let us now look at the complete picture. Figure 5.20 illustrates pitching moment and lift coefficient against angle of incidence. This shows that as incidence is increased toward the stall there is a stable nose down pitching tendency. Notice particularly the increase in stable slope of Cm just before the stall. This is typical of some aircraft types and reflects the success of the designer in achieving an inboard stall first, thus producing a nose down tendency. After the stall, however, the aeroplane pitches up at increasing angles of incidence until it reaches a more or less stable state at around say 30 degrees. So far so good, for a purely academic illustration. In real life, however, the manoeuvre is more treacherous than the illustration suggests, for two reasons stemming from the same source. It has been explained previously that below, say roughly 1.4 Vs, an increase in incidence causes drag to increase faster than lift and thus the aeroplane tends to sink. It is most important to realize that this increasing sinking tendency, at a constant pitch attitude, results in a rapid increase in incidence as the flight path becomes deflected downwards. Furthermore, once the stall has developed and a lot of lift has been lost, the aeroplane will start to sink rapidly and this is accompanied by a rapid increase in incidence.
This matter of a downward inclining flight path producing rapid increases in incidence compounds the entry to, and the progression of, the super-stall. It must be emphasised again that this can occur without the need for an excessively nose high pitch attitude. It can happen on some types a an apparently not abnormal pitch attitude, and it is this quality that can mislead the pilot because it looks very similar to the beginning of a normal recovery.”
Now skipping down a half paragraph, “There is no point in discussing the irrecoverable case any further, except perhaps to say that those aeroplanes which have been lost in such manoeuvres finally reached the ground substantially level laterally, having defied all efforts to roll or spin them out of the stabilized condition; only slightly nose down in pitch, with little or no forward speed; at an extremely high incidence; rotating only very slowly in yaw; with (in one case) all the engines flamed out because of being exposed to such massive angles of incidence; and finally with an enormous vertical velocity.”
I would especially appreciate comment from A330 knowledgeable individuals on the availability of the 3 pieces of information that I suspect are not continuously displayed in the cockpit.
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Super-stall
RE: Machinbird #493
Perhaps two additional sentences from the section "The super-stall" in D.P.Davies' book will help to put the whole thing into perspective:
"Recovery from a super-stall should not really have a place in this book since the book is written for airline pilots who have every right to say that they have no interest in an aeroplane which can achieve a super-stalled condition."
and two pages later:
"It must be emphasised that we are still in the rather academic field because an aeroplane capable of super-stalling would not, of course, be certificated without adequate protection".
Regards,
HN39
Perhaps two additional sentences from the section "The super-stall" in D.P.Davies' book will help to put the whole thing into perspective:
"Recovery from a super-stall should not really have a place in this book since the book is written for airline pilots who have every right to say that they have no interest in an aeroplane which can achieve a super-stalled condition."
and two pages later:
"It must be emphasised that we are still in the rather academic field because an aeroplane capable of super-stalling would not, of course, be certificated without adequate protection".
Regards,
HN39
Last edited by HazelNuts39; 14th Mar 2010 at 11:17. Reason: correction of typo
BOAC;
The trend of the discussion is frustrating but so is the absence of information. There is nothing to go on except the wreckage, the ACARS series, the two BEA Interim Reports and the thirteen other similar events which occurred to the A330.
More to the point, I think it is important for understanding the airplane that system and handling questions be elaborated upon but not with the intent of "solving" causes. So much has been written about this accident out of just plain ignorance of the airplane and how airlines work and how accident investigation works that, for those with the patience anyway, it is important to remain in the dialogue. Understanding this airplane is important if we are to triage the many possible causal pathways to what happened at 02:10Z and the ensuring six minutes or so, the only important point since last June.
I happen to think, (and have said why, above) that the BEA Interim Reports have something to say regarding how the aircraft struck the water and that may narrow the antecedents so perhaps the debate is in this sense, worthwhile and sometimes the devil does indeed lie in the minutae, among the angels...
Far more important is to identify what went wrong at cruise altitude, examine the software interactions involved and correct any deficiencies. If/when more bits/recorders are located we move on to the detail of the impact. This really should be the thrust of this thread - in my opinion.
More to the point, I think it is important for understanding the airplane that system and handling questions be elaborated upon but not with the intent of "solving" causes. So much has been written about this accident out of just plain ignorance of the airplane and how airlines work and how accident investigation works that, for those with the patience anyway, it is important to remain in the dialogue. Understanding this airplane is important if we are to triage the many possible causal pathways to what happened at 02:10Z and the ensuring six minutes or so, the only important point since last June.
I happen to think, (and have said why, above) that the BEA Interim Reports have something to say regarding how the aircraft struck the water and that may narrow the antecedents so perhaps the debate is in this sense, worthwhile and sometimes the devil does indeed lie in the minutae, among the angels...
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HN39
First "super-stall" is not a well defined term. Perhaps it should be defined as an aircraft that will lock itself into an irrecoverable stall (one that cannot be recovered from no matter what combination of control inputs are made).
Deep stalls are generally achievable on swept wing aircraft by virtue of the pitch up characteristic at stall. Deep stalls have no place in airline flying. Airbus has built a series of protections into their flight control system to prevent achieving a deep stall. In Alternate law and Direct Law, the protections revert to IAS basis instead of AOA. It may be that even in Normal law, erroneous airspeed indications that pass the validation criterea could create a stalled condition. When a system such as the airspeed input is triple redundant, it is obviously very critical that it remain functional. It is pretty clear from the ACARS messages that it did not.
That is a certification issue that has been fixed (perhaps) by pitot probe diversity between manufacturers.
If the initial phase of erroneous airspeeds was biased to the high side, the aircraft would begin decelerating and the THS would be trimming nose up. The only clue would be an increasing deck angle and reduced power settings.. If at this point the "pinball show" commenced there would not be a lot of time to sort it all out before the aircraft decelerated into a stall.
Would you care to comment on the availability of the following 3 parameters in the A330 cockpit. I have never been in an A330 cockpit, but from other postings, it appears that there is a multifunction display that can display engine parameters or other data. I suspect that things like THS position and AOA also fall into this category and that none of them are displayed full time in the cockpit.
Not trying to be a wise guy here. Others have posed similar questions. Just trying to assemble the evidence into a sensible scenario.
First "super-stall" is not a well defined term. Perhaps it should be defined as an aircraft that will lock itself into an irrecoverable stall (one that cannot be recovered from no matter what combination of control inputs are made).
Deep stalls are generally achievable on swept wing aircraft by virtue of the pitch up characteristic at stall. Deep stalls have no place in airline flying. Airbus has built a series of protections into their flight control system to prevent achieving a deep stall. In Alternate law and Direct Law, the protections revert to IAS basis instead of AOA. It may be that even in Normal law, erroneous airspeed indications that pass the validation criterea could create a stalled condition. When a system such as the airspeed input is triple redundant, it is obviously very critical that it remain functional. It is pretty clear from the ACARS messages that it did not.
That is a certification issue that has been fixed (perhaps) by pitot probe diversity between manufacturers.
If the initial phase of erroneous airspeeds was biased to the high side, the aircraft would begin decelerating and the THS would be trimming nose up. The only clue would be an increasing deck angle and reduced power settings.. If at this point the "pinball show" commenced there would not be a lot of time to sort it all out before the aircraft decelerated into a stall.
Would you care to comment on the availability of the following 3 parameters in the A330 cockpit. I have never been in an A330 cockpit, but from other postings, it appears that there is a multifunction display that can display engine parameters or other data. I suspect that things like THS position and AOA also fall into this category and that none of them are displayed full time in the cockpit.
Not trying to be a wise guy here. Others have posed similar questions. Just trying to assemble the evidence into a sensible scenario.
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One... I agree the "super-stall" terminology shouldn't really be used... It applies / applied mostly to T-tailed aircraft where the aircraft ended up in a 'locked-in' high-AoA attitude with the stalled airflow from the wing totally blanking the horizontal tail / elevator, leaving the aircraft to mush into the ground without any pitch control left to the pilot.
Two...
Deep stalls are generally achievable on swept wing aircraft by virtue of the pitch up characteristic at stall. Deep stalls have no place in airline flying. Airbus has built a series of protections into their flight control system to prevent achieving a deep stall.
I've worked on AFCS a long way back, not on the current video game cockpits.
I'm not trying to be a wise guy either, just to understand.... which is why I'm still following this thread, BTW.
CJ
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'Arm 36 g' again!
HN39 ...
It turns out that my first calculation was too simplistic and it has therefore been deleted. The FAR Part 25 regulations specify an ultimate load corresponding to 24*1.5=36 g. The rudder and supporting hinge brackets must be able to support an inertia ultimate load acting parallel to the hinge line of 24*1.5=36 times the weight of the rudder. Since Arm 36g is at an angle of 38 degrees to the rudder hinge line, 120 000 N in the direction of that arm corresponds to 94 561 N along the rudder hingeline, and hence to a rudder mass of 268 kg.
It turns out that my first calculation was too simplistic and it has therefore been deleted. The FAR Part 25 regulations specify an ultimate load corresponding to 24*1.5=36 g. The rudder and supporting hinge brackets must be able to support an inertia ultimate load acting parallel to the hinge line of 24*1.5=36 times the weight of the rudder. Since Arm 36g is at an angle of 38 degrees to the rudder hinge line, 120 000 N in the direction of that arm corresponds to 94 561 N along the rudder hingeline, and hence to a rudder mass of 268 kg.
Talk about left turns, right turns, red herrings and tangents - we've had the lot!
mm43
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THS position
Machinbird ...
The Perpignan accident involving A320 D-AXLA, although a different Airbus model, indicated to me the amount of pitch authority Airbus builds into their THS designs and how an aircraft could be left with full nose up trim and only the manual trim wheel available to reduce this trim. When added to a triple pitot tube freeze up, and a full trim tank, the resulting cockpit “pinball show” could easily confuse an unsuspecting aircrew until it was too late. I also suspect cockpit design made it too hard to get the critical information needed (actual power setting, THS position, actual angle of attack) and as a result, the aircrew was unable to develop the big picture of what was happening. I also suspect that the A-330 can be held in a deep stall by full nose up trim and an aft CG and yet be stabilized in a relatively stable normal flight attitude by the flight control system.
The Perpignan accident involving A320 D-AXLA, although a different Airbus model, indicated to me the amount of pitch authority Airbus builds into their THS designs and how an aircraft could be left with full nose up trim and only the manual trim wheel available to reduce this trim. When added to a triple pitot tube freeze up, and a full trim tank, the resulting cockpit “pinball show” could easily confuse an unsuspecting aircrew until it was too late. I also suspect cockpit design made it too hard to get the critical information needed (actual power setting, THS position, actual angle of attack) and as a result, the aircrew was unable to develop the big picture of what was happening. I also suspect that the A-330 can be held in a deep stall by full nose up trim and an aft CG and yet be stabilized in a relatively stable normal flight attitude by the flight control system.
My reference is http://www.andytracy.net/files/27FLTCTL.doc , and I'm sure there will be further discussion.
mm43