Mid-air collision over Brasil
Psychophysiological entity
I personally doubt that the impact scenarios discussed latterly in this thread would down the Boeing. In the mathematical model earlier, the energies would be theoretically focused to contact surface areas. This would not happen, though such a hypotheses has to be built from some foundation of course.
The very nature of the structures involved would mean that the air would play a very significant part, not only in the destruction of these airfoils, but also in the dissipation of energies after collision: as the component parts were distorted and started splitting, the first leakage would cause an almost explosive swelling and resultant disintegration of the winglet before it had progressed very far into the Boeing's wing.
As we all know, many severely damaged aircraft have made it back to base, some older slower types having less than half of one wing left on a given side. There has to be a vulnerable and indeed vital component having suffered damage. Aircraft have so many Achilles' heels.
The very nature of the structures involved would mean that the air would play a very significant part, not only in the destruction of these airfoils, but also in the dissipation of energies after collision: as the component parts were distorted and started splitting, the first leakage would cause an almost explosive swelling and resultant disintegration of the winglet before it had progressed very far into the Boeing's wing.
As we all know, many severely damaged aircraft have made it back to base, some older slower types having less than half of one wing left on a given side. There has to be a vulnerable and indeed vital component having suffered damage. Aircraft have so many Achilles' heels.
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This just hit the old in-box...
http://i80.photobucket.com/albums/j1...vitor/gear.jpg
http://i80.photobucket.com/albums/j1...vitor/gear.jpg
Gear down could mean;
A: He was trying to land. This means he had some control of the aircraft.
B: There is an option of lowering the gear for/during emergency descent on the NG if structural integrity is in doubt. Gear down speed is .82 so normally below your cruise speed.
C: Damage to the uplock(s).
Can somebody remind me what the birdstrike criteria are for the engine of a 737 diameter. One kg and 200 kts strikes me from memory. I will repost the right answer when my bird specialist is awake.
20kg of winglet down the engine may well cause total detachment, in the designed failure manner shown on the photos.
OK, looking at the simulation, I could go with that, as opposed to my blind thought on the underside/engine strike on the 737. Sometimes you forget how big the 145 is. It just feels very small when you get to sit in one for a while at my height!
The impact of the frangible winglet with the wing will easily lead to the winglet of the Legacy being smashed off, no problem. The outer element of the T tail being lost as well, fine. However, when the winglet has smashed its way through the slats, it comes across the main wing box. These are very very strong. Something just feels funny about the winglet doing sufficient damage to destroy enough of the wing to make a difference at this point. Certainly when compared to the fin of the 757 (two tonnes of Seattle's finest) hitting the front of the 154 wing root, it did not do that much damage to the wing box, from memory. Maybe the ironworks from Tupolev win out over the NG wing here.
Now, the loss of the winglet on the NG wing is an interesting proposition. I would have assumed that the change in lift at the wing extremity should be counteractable by normal roll control systems. No doubt Mr Blended Winglets will be busy for the next few days.
At least these aircraft should not have the Gillham code and the FL 350/370 problem.
Also remember that when you see an aircraft 1000 feet below you, it looks as if it is on the same level, such is the deception of the false horizon and the nose up attitudes. At least in some cases.
Does anybody know what the factory acceptance tests are for TCAS. Just wondering if the Legacy had a failed unit of some form or other, and they had never seen another aircraft on the display, because they were not expecting to. So, plug in the bench tests stuff and it looks ok, but is there a practical air test of it? Not necessarily in terms of resolution, but just being aware of other traffic?
20kg of winglet down the engine may well cause total detachment, in the designed failure manner shown on the photos.
OK, looking at the simulation, I could go with that, as opposed to my blind thought on the underside/engine strike on the 737. Sometimes you forget how big the 145 is. It just feels very small when you get to sit in one for a while at my height!
The impact of the frangible winglet with the wing will easily lead to the winglet of the Legacy being smashed off, no problem. The outer element of the T tail being lost as well, fine. However, when the winglet has smashed its way through the slats, it comes across the main wing box. These are very very strong. Something just feels funny about the winglet doing sufficient damage to destroy enough of the wing to make a difference at this point. Certainly when compared to the fin of the 757 (two tonnes of Seattle's finest) hitting the front of the 154 wing root, it did not do that much damage to the wing box, from memory. Maybe the ironworks from Tupolev win out over the NG wing here.
Now, the loss of the winglet on the NG wing is an interesting proposition. I would have assumed that the change in lift at the wing extremity should be counteractable by normal roll control systems. No doubt Mr Blended Winglets will be busy for the next few days.
At least these aircraft should not have the Gillham code and the FL 350/370 problem.
Also remember that when you see an aircraft 1000 feet below you, it looks as if it is on the same level, such is the deception of the false horizon and the nose up attitudes. At least in some cases.
Does anybody know what the factory acceptance tests are for TCAS. Just wondering if the Legacy had a failed unit of some form or other, and they had never seen another aircraft on the display, because they were not expecting to. So, plug in the bench tests stuff and it looks ok, but is there a practical air test of it? Not necessarily in terms of resolution, but just being aware of other traffic?
You are reaching way too far in your suppositions having to do with engines.
Modern engines don't blow up and detach themselves from wings, they do get thrown off however.
Rather than ask about bird ingestion criteria, just review the history having to do with this model. zilch except for a few broken fanblades and nothing even close to downing a B737 due to collateral damage.
I really don't mind some degree of speculation filling in one gap in knowledge at a time with a what-if. But to string a link of highly speculative what-ifs is reaching.
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I can think of two fairly large jets being brought down by collision with smaller planes
PSA 727/C172 San Diego, mentioned earlier
DC9/Piper Archer over LA/ Ceritos california.
the small planes involved were much smaller than the large jets involved. the odd thing about this incident is that the legacy survived with such little damage.
perhaps the legacy created a force upon the boeing's rudder, causing a reversal like the crash near Pittsburgh, PA. perhaps the legacy cut vital lines (hydraulic or control)
j
PSA 727/C172 San Diego, mentioned earlier
DC9/Piper Archer over LA/ Ceritos california.
the small planes involved were much smaller than the large jets involved. the odd thing about this incident is that the legacy survived with such little damage.
perhaps the legacy created a force upon the boeing's rudder, causing a reversal like the crash near Pittsburgh, PA. perhaps the legacy cut vital lines (hydraulic or control)
j
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Perhaps, as the Embraer crossed in front of the 73, the left winglet gashed the No2 engine and the left side stab tip cut into the flight deck. The stab is a lot stronger than the winglet which would explain the fact that it seems to have little damage.
This would explain the lack of any RT after the incident.
This would explain the lack of any RT after the incident.
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Very interesting picture!
Gear down could mean;
A: He was trying to land. This means he had some control of the aircraft.
B: There is an option of lowering the gear for/during emergency descent on the NG if structural integrity is in doubt. Gear down speed is .82 so normally below your cruise speed.
C: Damage to the uplock(s).
Gear down could mean;
A: He was trying to land. This means he had some control of the aircraft.
B: There is an option of lowering the gear for/during emergency descent on the NG if structural integrity is in doubt. Gear down speed is .82 so normally below your cruise speed.
C: Damage to the uplock(s).
Looks like the right wing is "intacted" while the left wing was ripped off... maybe a failed forced land where they hit a tree and flipped upside down. In this case don't you think that to try to ditch on a river would be a better option if you had a chance to?
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I am well aware that modern engines do not usually "blow up" and detach themselves from wings. However, the accident is well beyond design case. The design case is for engine seizing, bird strikes and general turbulence/manoeuvring. A winglet ingestion is well beyond the bird strike case. It is likely that the engine internals would disintegrate if the winglet were to enter.
The main reason for engines falling off would be massive yaw rates. The 757 over Germany seemed to suffer from this. As you may be aware, the yaw rate criteria are significantly less than in other dimensions. The engines have detached and relatively cleanly, which indicates the design break off manner. I know that throwing winglets into engines is not part of the certification of the aircraft, and with the kinetic energy impacts being discussed, it is a possibility, and that is all.
I was looking at possible geometry of encounters which could lead to the damage seen on the surviving aircraft. It is not unusual in mid-air collisions to get some angle of bank involved at the last moment for head on encounters. Hence the damage could be representative of a collision of winglet with engine.
What has caused all the inspection panels to blow out from the port wing and not the starboard? That, in itself, may indicate a wing encounter rather than engine. However, I would need more photographs.
Does anybody know if the NGs can survive detachment of a single engine or is the roll moment too large for the control authority?
The main reason for engines falling off would be massive yaw rates. The 757 over Germany seemed to suffer from this. As you may be aware, the yaw rate criteria are significantly less than in other dimensions. The engines have detached and relatively cleanly, which indicates the design break off manner. I know that throwing winglets into engines is not part of the certification of the aircraft, and with the kinetic energy impacts being discussed, it is a possibility, and that is all.
I was looking at possible geometry of encounters which could lead to the damage seen on the surviving aircraft. It is not unusual in mid-air collisions to get some angle of bank involved at the last moment for head on encounters. Hence the damage could be representative of a collision of winglet with engine.
What has caused all the inspection panels to blow out from the port wing and not the starboard? That, in itself, may indicate a wing encounter rather than engine. However, I would need more photographs.
Does anybody know if the NGs can survive detachment of a single engine or is the roll moment too large for the control authority?
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We have alluded to low and medium altitude incidents, reviewing straight impacts of various sorts.
Is someone out there equipped to consider the implications of transonic airflow when two wings are passing as in this high altitude situation ?
In the very tightest case you have two boundary layers passing at relative supersonic speeds. Further apart there will surely be venturi-effect acceleration between the nearest parts of each aircraft, perhaps generating a local shock wave. Might this be sufficient to cause wing panels to pop out ?
If that might happen, hinges and control surfaces might also be affected.
Is someone out there equipped to consider the implications of transonic airflow when two wings are passing as in this high altitude situation ?
In the very tightest case you have two boundary layers passing at relative supersonic speeds. Further apart there will surely be venturi-effect acceleration between the nearest parts of each aircraft, perhaps generating a local shock wave. Might this be sufficient to cause wing panels to pop out ?
If that might happen, hinges and control surfaces might also be affected.
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... too many variables and unknowns to really understand the pre and post MAC events yet!
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.. the centre section photo does not reveal anything meaningful. Any or all of those visible clues may have resulted from break-up and/or impact. The left main position may have resulted from side load impact with the terrain, as could be the case with the deformation of the left side spar.
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The blown out inspection panels on the left wing are interesting though!
.... I would have thought that would only occur as a result of internal outward pressure (air or fuel)?!
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... FDR and CVR data will reveal bank angle at the time of collision (as well as a host of other relevant information) .. from the looks of it thus far, IMHO one, or the other, or both had some bank angle on, either that or they were both extremely unlucky (or in the case of the Embraer occupants .. lucky)!
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... one thing is certain, if any part of the Embraer met with any part of the pressure vessel of the the B738 .... it was all over then and there for them
.... The pressure differential and explosive out flow .... well .. you all know the results of something like that at FL360 (the ‘china’ 74 comes to mind)!!
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.... there are many scenarios that may have precluded a post collision broadcast by the 73 crew, however given the (relatively) slight winglet and horizontal stab damage on the Embraer, the impact points on the 73 must have been critical!
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.. the lack of RT could tend to lend strength to a sudden and perhaps explosive break-up sequence ... although electrical bus interrupt could do any number of things to any number of systems including of course comm's .. .
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.. then there is the witness report of the aircraft (or part of it) spinning?!
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..that account and the 'flat' impact of the centre section reminded me of the BOAC B707 that flew through the mountain wave near Mt FUJI! .. in that sequence the sudden side load on the vertical stab and engine pylons had them all off in short time, leaving the remainder of the wings and fuse to descend in a slow rotation flat spin to ground impact ... (still have that imprint of the twin boggy gear legs sitting in the wells) ... this has a very similar feel to it!!
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... the earlier photo of the vertical stab seems to indicate it was reasonably intact .... was it located near the centre section??
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.... reason I ask is that after rapid break-up, the empennage parts are often found closest (geographically) to the point of break-up with the remaining sections further away!
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.. if the fin was found a distance away from the hull and closer to the MAC position ….. yaw, roll (sudden and dramatic due wing sweep) and rapid break-up are highly probable!
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.... if the empennage parts are with (close to) the rest of the hull, you could almost (and I say ALMOST) rule out explosive and/or loss of control break-up!!
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... in any event … tis all conjecture until the known’s are known!
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.. the centre section photo does not reveal anything meaningful. Any or all of those visible clues may have resulted from break-up and/or impact. The left main position may have resulted from side load impact with the terrain, as could be the case with the deformation of the left side spar.
.
The blown out inspection panels on the left wing are interesting though!
.... I would have thought that would only occur as a result of internal outward pressure (air or fuel)?!.
... FDR and CVR data will reveal bank angle at the time of collision (as well as a host of other relevant information) .. from the looks of it thus far, IMHO one, or the other, or both had some bank angle on, either that or they were both extremely unlucky (or in the case of the Embraer occupants .. lucky)!
.
... one thing is certain, if any part of the Embraer met with any part of the pressure vessel of the the B738 .... it was all over then and there for them
.... The pressure differential and explosive out flow .... well .. you all know the results of something like that at FL360 (the ‘china’ 74 comes to mind)!! .
.... there are many scenarios that may have precluded a post collision broadcast by the 73 crew, however given the (relatively) slight winglet and horizontal stab damage on the Embraer, the impact points on the 73 must have been critical!
.
.. the lack of RT could tend to lend strength to a sudden and perhaps explosive break-up sequence ... although electrical bus interrupt could do any number of things to any number of systems including of course comm's .. .
.
.. then there is the witness report of the aircraft (or part of it) spinning?!
.
..that account and the 'flat' impact of the centre section reminded me of the BOAC B707 that flew through the mountain wave near Mt FUJI! .. in that sequence the sudden side load on the vertical stab and engine pylons had them all off in short time, leaving the remainder of the wings and fuse to descend in a slow rotation flat spin to ground impact ... (still have that imprint of the twin boggy gear legs sitting in the wells) ... this has a very similar feel to it!!
.
... the earlier photo of the vertical stab seems to indicate it was reasonably intact .... was it located near the centre section??
.
.... reason I ask is that after rapid break-up, the empennage parts are often found closest (geographically) to the point of break-up with the remaining sections further away!
.
.. if the fin was found a distance away from the hull and closer to the MAC position ….. yaw, roll (sudden and dramatic due wing sweep) and rapid break-up are highly probable!
.
.... if the empennage parts are with (close to) the rest of the hull, you could almost (and I say ALMOST) rule out explosive and/or loss of control break-up!!
.
... in any event … tis all conjecture until the known’s are known!
Last edited by Scurvy.D.Dog; 2nd Oct 2006 at 12:56. Reason: Spellin'
For Portuguese readers:
http://oglobo.globo.com/pais/mat/200.../285929322.asp
The article indicates the Legacy was at FL370, still under Brasilia ATC, while the 738 had requested and been cleared by Manaus ATC to climb from FL350 to 390.
An article in another newspaper quotes the president of Infraero suggesting the most likely scenario as that of the Legacy's winglet shearing hydraulic/electric lines in the 738's horizontal stabilizer.
http://oglobo.globo.com/pais/mat/200.../285929322.asp
The article indicates the Legacy was at FL370, still under Brasilia ATC, while the 738 had requested and been cleared by Manaus ATC to climb from FL350 to 390.
An article in another newspaper quotes the president of Infraero suggesting the most likely scenario as that of the Legacy's winglet shearing hydraulic/electric lines in the 738's horizontal stabilizer.
I'm in one of those moods
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.... awww ****e
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... if that is accurate, then it seems (in this case) serviceable TCAS was more important than ever !!
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.. what of the TCAS OFF selection issue?? and the supposed climb of the Embraer?? ... anything in the local press about that stuff??
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... if that is accurate, then it seems (in this case) serviceable TCAS was more important than ever !!
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.. what of the TCAS OFF selection issue?? and the supposed climb of the Embraer?? ... anything in the local press about that stuff??
Last edited by Scurvy.D.Dog; 2nd Oct 2006 at 13:31. Reason: addition
Pressure vessel decompression is of little significance in the breakup. There really is no such thing as a hole in the fuselage causing a decompression to finish the job.
With so little damage to the plane that landed the most one would expect is extremely localized damage to the B737. However the real issue is what came first. If the B737 was first ala the breakup of PA103 or TWA800 then it's possible (I have no idea how probable) that small debris might have struck the other plane.
From the pic, the damage to the left wing of the B737 doesn't look like impact damage, but instead more like buckling and overload ala the video of the B777 wing overload test.
With so little damage to the plane that landed the most one would expect is extremely localized damage to the B737. However the real issue is what came first. If the B737 was first ala the breakup of PA103 or TWA800 then it's possible (I have no idea how probable) that small debris might have struck the other plane.
From the pic, the damage to the left wing of the B737 doesn't look like impact damage, but instead more like buckling and overload ala the video of the B777 wing overload test.
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Legacy's winglet shearing hydraulic/electric lines in the 738's horizontal stabilizer.
Looking at the damage to the EMB and the way the 737 crashed (upside down with the gear out) maybe the EMB winglet sliced through just forward of the AFT pressure bulkhead causing an explosive decompression. The mass flow of air may have then caused extensive damage to the tailsection similar to the JAL123 accident. Dropping the gear may have been an attempt to regain control.
If the 737 had lost pitch control due to damage to the tail, it would presume it still had roll control. As mentioned, the 737 does NOT need hydraulic fluid to remain controllable. With the majority of the tail missing, it’s doubtful whether the flight crew could control the aircraft with roll and thrust alone.
This is obviously just pure guesswork on my behalf and I hope the investigators find and release the cause ASAP so we can debate rather than speculate.
Condolences to all involved.
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SDD, from a report into the Uberlingen mid-air:
Such was the case in this mid-air collision. The TCAS worked as designed. But, as in most accidents, a range of insidious policy, training and procedural issues are involved. This accident was no exception. It was one where other breakdowns overwhelmed the last ditch defense that TCAS was intended to provide.
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Pressure vessel decompression is of little significance in the break-up. There really is no such thing as a hole in the fuselage causing a decompression to finish the job.
... opening up the can is only part of the issue, pressure ripping and skin section exposure to air stream and tare away etc are some of the others
that small debris might have struck the other plane.
the president of Infraero suggesting the most likely scenario as that of the Legacy's winglet shearing hydraulic/electric lines in the 738's horizontal stabilizer.
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London Mil ... quite so!
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... is the report from the Legacy pilot after landing of TCAS being OFF a furphy then??
Last edited by Scurvy.D.Dog; 2nd Oct 2006 at 14:01. Reason: addition
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Were they flying on an airway?
One could also raise the general question concerning the wisdom of flying directly on a bidirectional airway in RVSM airspace (in this instance uncrowded), considering the accuracy of modern navigation systems, and not somewhat offset? Is it allowed to track offset to an airway centerline? Does exact navigation reduce the error margins for MAC in RVSM airspace in the event of a level bust?
One could also raise the general question concerning the wisdom of flying directly on a bidirectional airway in RVSM airspace (in this instance uncrowded), considering the accuracy of modern navigation systems, and not somewhat offset? Is it allowed to track offset to an airway centerline? Does exact navigation reduce the error margins for MAC in RVSM airspace in the event of a level bust?
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As proposed by Profit Max.
There must be a dozen different ways the two aircraft could have made contact resulting in the known damage to the Legacy, but still leaving the Legacy flyable.
However, we believe the Legacy was straight and level, (and, very likely, so was the 737) in which case there may be only one possibility, which could well be supported by the missing panels on the 737 port side wing wreckage.
There must be a dozen different ways the two aircraft could have made contact resulting in the known damage to the Legacy, but still leaving the Legacy flyable.
However, we believe the Legacy was straight and level, (and, very likely, so was the 737) in which case there may be only one possibility, which could well be supported by the missing panels on the 737 port side wing wreckage.
Last edited by forget; 2nd Oct 2006 at 15:09.