Mid-air collision over Brasil
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just for the record ... isn't it magnetic course and not magnetic heading?
one could make good a course of 350 degrees by flying heading 001degrees...depending on the wind
one could make good a course of 350 degrees by flying heading 001degrees...depending on the wind
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That is the question. Why ATC would assign them FL 370? That is why this accident happened. Some one put them in an unappropriated level. Result: mid-air collision.
When they assigned FL370 from Brasilia to Manaus? When this level was assigned?
What you must understand is that ATC assigned the Legacy FL 370. The crew of the Legacy cannot leave the last assignined Flight Level in normal circumstances, which both crews had no reason believe that they were not in normal operations, without permission of ATC.
The requested Flight Level is immaterial to this accident. The Flight Level assignined by ATC has everything to do with this accident.
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I heard the recording
The recording of the clearance from ATC in São Jose shows the conversation between the ATC and the pilots, after taking off. The recording is there at the Traffic Control Center. I will try to find it somewhere.
I found it. This was at Folha de São Paulo describing how the Air Force acknowledged that the ATC in São Jose cleared the Legacy pilots to fly to Manaus at 370 (in Brazilian Portuguese):
http://www1.folha.uol.com.br/folha/c...5u127785.shtml
Insofar as I know, no. No big warning. An Air Force officer has suggested this, that when a transponder is OFF as it was the case, an alarm would be heard loud and clear. But not only was the Z there (360Z360) but also there was indication that the transponder was off (+ nor surrounded by a circle). For almost one hour!
Yes, the Air Traffic Control in Brazil needs to be investigated in all levels: equipment, software and personal. I hope this is going to happen as Brazil is trying to fix this problems. Slowly they are changing things and I am sure that they will succeed.
I found it. This was at Folha de São Paulo describing how the Air Force acknowledged that the ATC in São Jose cleared the Legacy pilots to fly to Manaus at 370 (in Brazilian Portuguese):
http://www1.folha.uol.com.br/folha/c...5u127785.shtml
The " clearly" is what is most probably lacking in this ATC system. . How often a normal lack of Mode C interrogation return will provide a Z ? 10 times a day ? 100 times a day ? Is it a bright flashing letter coming on the screen if the Z remains for more than let's say , 3 returns , or 3 minutes...?
Yes, the Air Traffic Control in Brazil needs to be investigated in all levels: equipment, software and personal. I hope this is going to happen as Brazil is trying to fix this problems. Slowly they are changing things and I am sure that they will succeed.
Last edited by marciovp; 1st Sep 2007 at 04:38. Reason: More data
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At jet speeds and under IFR conditions, it simply is not possible for aircraft by themselves to maintain enroute or terminal area separation without some outside agency or method providing guidance or rules that affirmatively enforce separation.
An expectation in IFR navigation, throughout the world, is that the air traffic control system acting through the various enroute and terminal area control facilities will take 'reasonable and prudent care' to provide separation between the various aircraft in the system at every point in time.
Surely the crews of the GOL 737 and the Embraer Legacy (who each knew nothing about existence, plans, intentions or position of the other) both had a belief that Brazil ATC was paying attention to their positions and progress via flight plans, radar surveillance, and controller oversight.
Perhaps I missed it somewhere in this long thread, but I do not recall that Brazil ATC made any effort to reposition the GOL airliner on the airway prior to the collision.
The record is becoming clearer in regard to "who knew what when". Clearly Brazil ATC had numerous indications that communications with the Embraer were 'irregular', with no reliable transponder data, no 2-way radio communication, and ambiguous indications in regard to the Embraer cruise altitude. The Legacy position on the airway seems to have been continuously available, however, from the long-range surveillance radar data serving the region.
Is it not true that Cindacta had normal and continuous 3-dimensional position information and voice communications with the GOL 737? Why did ATC not provide some guidance to the GOL flight to change course slightly as the two aircraft neared each other, so as to sidestep the passenger airliner from the airway when another aircraft was known to be coming from the opposite direction at approximately the same altitude and not in communication with ATC.
A couple of gentle turns given to the 737 to position it well clear of the airway center during the time of convergence would have protected both aircraft from the events that followed. This kind of precautionary separation is a common practice everywhere I have flown. Why did Brazil ATC do nothing to inform GOL regarding the traffic and to provide positive separation for the two aircraft as their paths crossed?
An expectation in IFR navigation, throughout the world, is that the air traffic control system acting through the various enroute and terminal area control facilities will take 'reasonable and prudent care' to provide separation between the various aircraft in the system at every point in time.
Surely the crews of the GOL 737 and the Embraer Legacy (who each knew nothing about existence, plans, intentions or position of the other) both had a belief that Brazil ATC was paying attention to their positions and progress via flight plans, radar surveillance, and controller oversight.
Perhaps I missed it somewhere in this long thread, but I do not recall that Brazil ATC made any effort to reposition the GOL airliner on the airway prior to the collision.
The record is becoming clearer in regard to "who knew what when". Clearly Brazil ATC had numerous indications that communications with the Embraer were 'irregular', with no reliable transponder data, no 2-way radio communication, and ambiguous indications in regard to the Embraer cruise altitude. The Legacy position on the airway seems to have been continuously available, however, from the long-range surveillance radar data serving the region.
Is it not true that Cindacta had normal and continuous 3-dimensional position information and voice communications with the GOL 737? Why did ATC not provide some guidance to the GOL flight to change course slightly as the two aircraft neared each other, so as to sidestep the passenger airliner from the airway when another aircraft was known to be coming from the opposite direction at approximately the same altitude and not in communication with ATC.
A couple of gentle turns given to the 737 to position it well clear of the airway center during the time of convergence would have protected both aircraft from the events that followed. This kind of precautionary separation is a common practice everywhere I have flown. Why did Brazil ATC do nothing to inform GOL regarding the traffic and to provide positive separation for the two aircraft as their paths crossed?
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Sdruvss,
I have explained to you the protocols on clearances; so has ATC Watcher, and so has con-pilot. I cannot understand why you seem to have difficulty with this information.
We need to be working from the same information. Maybe you could read the NTSB publications on this. They were published on request of CENIPA. They contain much of the pertinent information. Here is a citation from the Factual Report, released last October, if I remember rightly.
Is that clear enough? They were cleared to and confirmed FL 370, and on the check in with the next controller they reported level at FL 370. They requested no new flight level; ATC gave them no instruction for a change of flight level.
And that is the state of the clearance when the collision took place. That is fact.
This is, to most IF-rated pilots and controllers all over the world, unambiguous. The aircraft was cleared to FL 370 by the usual procedures; no further altitude clearance was issued by ATC.
The question is, then, what N600XL should have done. This is, to most IF-rated pilots and controllers all over the world, also clear. He stays at FL 370 until he is cleared to another flight level. ATC Watcher has pointed out, though, that new ICAO procedures contain provisions which may say something else. I understand that IFATCA has requested from the Brazilian authorities to say whether those new ICAO procedures were in force in Brasil at the time of the accident, and have until now received no reply. As I said, if an official request for clarification cannot be answered in the space of months, then even if these new ICAO procedures did happen to have been in force, how can these two pilots be expected to have known?
This is all just a repetition of stuff which has already been said, but with more words and lengthier citations. The discussion would be much more efficient if we could all read the canonical documents, and all accept certain basic facts about procedures under IFR.
PBL
I have explained to you the protocols on clearances; so has ATC Watcher, and so has con-pilot. I cannot understand why you seem to have difficulty with this information.
Originally Posted by Sdruvss
I’ve read all I could, everywhere, all newspapers and magazines and, controllers interview at TV, and didn't read it.
We need to be working from the same information. Maybe you could read the NTSB publications on this. They were published on request of CENIPA. They contain much of the pertinent information. Here is a citation from the Factual Report, released last October, if I remember rightly.
Originally Posted by NTSB Factual Report
After takeoff, N600XL was issued a number of interim altitudes during climb, all of which were read back. The flight was cleared to proceed direct to Araxa VOR (on airway UW2), and at 3:11 pm was cleared to climb to FL 370. At 3:33 pm, the aircraft levelled at FL 370.
........[Stuff about GOL 1907]..........
At 3:51 pm, an air traffic controller in the Brasilia ATC (CINDACTA 1) instructed N600XL to change frequencies to the next controller's sector. The crew of N600XL reported in on the assigned frequency that the flight was level at FL 370. ATC acknowledged and instructed the crew to "ident" (flash their transponder). Radar indicates that the ident was observed. This was the last two-way communication between N600XL and ATC. At this time the airplane was approximately 40 nautical miles south of BRS.
At 3:56 pm the Legacy N600XL passed BRS level at FL 370. There is no record of a request from N600XL to the control agencies to conduct a change of altitude, after reaching flight level 370. The crew made calls, but there is no communication in which they requested a change of flight level. There is also no record of any instruction from air traffic controllers at Brasilia Center to the aircraft, directing a change of altitude.
........[Stuff about GOL 1907]..........
At 3:51 pm, an air traffic controller in the Brasilia ATC (CINDACTA 1) instructed N600XL to change frequencies to the next controller's sector. The crew of N600XL reported in on the assigned frequency that the flight was level at FL 370. ATC acknowledged and instructed the crew to "ident" (flash their transponder). Radar indicates that the ident was observed. This was the last two-way communication between N600XL and ATC. At this time the airplane was approximately 40 nautical miles south of BRS.
At 3:56 pm the Legacy N600XL passed BRS level at FL 370. There is no record of a request from N600XL to the control agencies to conduct a change of altitude, after reaching flight level 370. The crew made calls, but there is no communication in which they requested a change of flight level. There is also no record of any instruction from air traffic controllers at Brasilia Center to the aircraft, directing a change of altitude.
And that is the state of the clearance when the collision took place. That is fact.
This is, to most IF-rated pilots and controllers all over the world, unambiguous. The aircraft was cleared to FL 370 by the usual procedures; no further altitude clearance was issued by ATC.
The question is, then, what N600XL should have done. This is, to most IF-rated pilots and controllers all over the world, also clear. He stays at FL 370 until he is cleared to another flight level. ATC Watcher has pointed out, though, that new ICAO procedures contain provisions which may say something else. I understand that IFATCA has requested from the Brazilian authorities to say whether those new ICAO procedures were in force in Brasil at the time of the accident, and have until now received no reply. As I said, if an official request for clarification cannot be answered in the space of months, then even if these new ICAO procedures did happen to have been in force, how can these two pilots be expected to have known?
This is all just a repetition of stuff which has already been said, but with more words and lengthier citations. The discussion would be much more efficient if we could all read the canonical documents, and all accept certain basic facts about procedures under IFR.
PBL
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PS: Clearance from Brasilia to Manaus (UZ6, FL370) shouldn’t be explicid confirmed by pilots? I’ve read it somewhere. (Don’t mind, don’t answer it, I took so much of your time. Remember PBL: biased scientific overconfidence)
Their transponder sent 370 and the software 360 (without requiring that this be confirmed by direct talk). This lasted seven minutes and ATC for some reason did not ask about the discrepancy...
But, enough is enough...let´s wait for the final report.
regards
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Regarding sdruvss
sdruvss just doesn't get it and clearly has no/limited knowledge of the "system".
Why bother with all this diatribe trying to answer the inane comments/remarks?
His only qualification is "location Sao Paulo". Given this particular subject and the history of how the matter has been handled in Brazil,that might also be a disqualifier unless there are some professional qualifications to offset.
Why bother with all this diatribe trying to answer the inane comments/remarks?
His only qualification is "location Sao Paulo". Given this particular subject and the history of how the matter has been handled in Brazil,that might also be a disqualifier unless there are some professional qualifications to offset.
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Originally Posted by Sdruvss
Now it becomes clear to me that Cindacta didn’t clear them from Brasilia to Manaus FL 370, wouldn’t clear if requested, but since Cindacta didn’t say it, this was assumed that they did.
N600XL was cleared to FL 370 at 3:11 pm by whomever he was then talking to (Sao Joao dos Campos?). Before he was told to contact Brasilia Center, the controller would have contacted Brasilia Center to perform the hand-off. This hand-off information contains the info that aircraft N600XL is level at FL 370, and when Brasilia accepts the hand-off, he accepts the obligation to keep the airspace at FL 370 on the route of flight clear for this aircraft (or to keep some other airspace clear and issue an amended clearance).
So, contrary to what you say, Brasilia Center had accepted the obligation to clear them at FL 370.
Originally Posted by Sdruvss
if I were the pilots I would be very worried
). It is routine procedure, practiced tens of thousands of times a day by thousands of pilots and controllers.PBL
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If you were an experienced instrument rated pilot, none of this would have worried you as procedure (until September 2006, that is ). It is routine procedure, practiced tens of thousands of times a day by thousands of pilots and controllers.
PBL
PBL
Yes I am an experienced instrument rated pilot... and on a truly world-wide basis.. but when cleared to a non-standard FL, although not 'worried'.. I am conscious of being non-std and always include the 'non-std' phrase when reading back the clearance.. and again include it on hand-over or in the event of joining another A/W at an intersection... required ?? No... maybe not... but unless you believe controllers are incapable of making errors it would seem good sense.. I would do this when working the London TMA ... arguably the best controllers on the planet... I would most certainly do it anywhere where either the language or comms are less than perfect... No reflection on any of the crews involved in this accident...we still don't know the full story...just a comment on PBLs post.
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Originally Posted by poorwanderingwun
I am an experienced instrument rated pilot... but when cleared to a non-standard FL, although not 'worried'.. I am conscious of being non-std and always include the 'non-std' phrase when reading back the clearance.. and again include it on hand-over or in the event of joining another A/W at an intersection.
I was responding to the word "worried", and you confirm what I said. We were also discussing the flight of N600XL with a neophyte who seems to be trying to find things procedurally incorrect with the way the pilots of N600XL executed IFR clearances.
I think people who fly all over the world learn certain techniques to improve their chances of not getting broadsided (in the general meaning of the word), and yours is one that people after GOL/Legacy might do well to emulate. After AA in Cali, many no longer took the word "Affirmative" to mean "Affirmative" when used by controllers in some S.Am. countries. And many are now taking seriously the thought of flying airways slightly offset; something that my instrument instructor suggested to me almost a quarter century ago.
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Well, I can't understand Portugese but I'd bet a penny to a dollar that it just repeats that same old bit of air law that the neophites can't seem to get their heads around... namely that if an airway has direction of flow between 000º and 179º then a/c should fly at an odd altitude, eg. 310, 330, 350 etc. and if between 180º and 359º then it should be even, eg. 320, 340, 360 etc.
Sadly, what the neophites seem unable to grasp is that whilst the above is true, it only applies strictly when in a non-radar environent. If, as has already been explained much more clearly than I am able to, the a/c is under positive radar control then those rules can be overuled by ATC.
As has been stated on here already, the flight was cleared by ATC to maintain FL370 and that overrides the air law being quoted above. Even if they knowingly suffered radio or comms failure, they should continue at the last assigned clearance. Only if they reach the limit of their clearance and they have lost comms should they revert to whatever is in their flight plan.
Now, I don't know why the neophites seem to be having so much trouble with this but I suspect that it is due to their total lack of experience of what the job is about. Add to that fact that we are dealing with a lawyer who probably is trying to make a literal interpretation without understanding the day to day operational requirements of ATC.
I suppose that patience is required, even though it is sometimes difficult, especially when so many neophites are trying to tell us how we should operate our a/c according to their very narrow and limited understanding of air law and 'the job'.
Sadly, what the neophites seem unable to grasp is that whilst the above is true, it only applies strictly when in a non-radar environent. If, as has already been explained much more clearly than I am able to, the a/c is under positive radar control then those rules can be overuled by ATC.
As has been stated on here already, the flight was cleared by ATC to maintain FL370 and that overrides the air law being quoted above. Even if they knowingly suffered radio or comms failure, they should continue at the last assigned clearance. Only if they reach the limit of their clearance and they have lost comms should they revert to whatever is in their flight plan.
Now, I don't know why the neophites seem to be having so much trouble with this but I suspect that it is due to their total lack of experience of what the job is about. Add to that fact that we are dealing with a lawyer who probably is trying to make a literal interpretation without understanding the day to day operational requirements of ATC.
I suppose that patience is required, even though it is sometimes difficult, especially when so many neophites are trying to tell us how we should operate our a/c according to their very narrow and limited understanding of air law and 'the job'.
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Oh...how complicate this gets...
João Batista da Silva Controlador de Tráfego Aéreo
November seis zero zero x-ray lima, ATC permissão para Eduardo Gomes, nível de vôo três sete zero direção Poços de Caldas,
November seis zero zero x-ray lima, ATC permissão para Eduardo Gomes, nível de vôo três sete zero direção Poços de Caldas,
The quote above is clear: "João Batista da SIlva ATC: November six zero zero x-ray lima, ATC permission for Eduardo Gomes (Manaus) flight level three seven zero direction Poços de Caldas."
I heard the dialogue between the pilots and ATC and if I am not mistaken they asked twice about the clearance.
The rest of the document from the CPI is again holding the pilots to follow the initial written flight plan and saying that they did not follow it. This has become the common criticism here: the original flight plan was not followed... little is said about the dialogue between the pilots and ATC in Sâo Jose. I hope they don´t erase this tape...
When they approached Brasilia they again told ATC that they were at 370. Brasilia wished them a good trip. Then their transponder showed for seven minutes that they were at 370 after passing Brasilia...etc, etc... I am not going to repeat myself.
Yes, I find that maybe the pilots could take the initiative in Brasilia and after to make sure they were flying in the proper altitude 370 and perhaps insist to know if this was the proper altitude. In hindsight everything is easy. But yes, maybe they could have done this... even though they knew that their altitude was being sent by their transponder (seven minutes) and they were in the radar of Cyndacta.
Well, let me admit that I got involved on this when I saw this prejudiced movement to blame the US pilots. I dislike prejudices of any kind. I was appaled whem in the first week after the accident the Minister of Defense in Brazil was in TV saying the the american pilots disconnected their transponder because they wanted to make stunts to test the new plane...
At that moment I decided to get involved.
But I am flexible and will change my present views when I see evidences for it. As for the dialogue between São Jose and the Pilots I will have to hear, myself, the tape before going for interpretations of what happened.
I am becoming found of Sdruvss (a Brazilian like me) andI am sorry we all can´t listen together to the tape with the conversation between TC in São Jose and Legacy. Perhaps someday...
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Translation
Sdruvss asked me to translate this conversation between himself and a Brazilian pilot:
I: WHat do you think about this accident?
Pilot: Yes, the Legacy messed up
I: Why?
Pilot: He entered in an odd level for Manaus
I: But the Legacy said that the controllers cleared this altitude
Pilot: Never. everyone knows that it is even for Manaus, and odd for Brasilia. it was the Legacy that did not understood the Cindacta and screw up. I never knew that Cindacta place anyone on odd to Manaus.
Eu: O que você acha deste acidente?
Piloto: É, o Legacy fez m....
Eu: Por que?
Piloto: Ele entrou no nível impar para Manaus
Eu: Mas o Legacy disse que os controladores que estabeleceram esta altitude.
Piloto: Nunca, todo mundo sabe que é par para Manaus e impar para Brasília, foi o Legacy que não entendeu o Cindacta e f... Eu nunca soube do Cindacta botar alguém em impar para Manaus.
Piloto: É, o Legacy fez m....
Eu: Por que?
Piloto: Ele entrou no nível impar para Manaus
Eu: Mas o Legacy disse que os controladores que estabeleceram esta altitude.
Piloto: Nunca, todo mundo sabe que é par para Manaus e impar para Brasília, foi o Legacy que não entendeu o Cindacta e f... Eu nunca soube do Cindacta botar alguém em impar para Manaus.
I: WHat do you think about this accident?
Pilot: Yes, the Legacy messed up
I: Why?
Pilot: He entered in an odd level for Manaus
I: But the Legacy said that the controllers cleared this altitude
Pilot: Never. everyone knows that it is even for Manaus, and odd for Brasilia. it was the Legacy that did not understood the Cindacta and screw up. I never knew that Cindacta place anyone on odd to Manaus.
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You missed the most important part of the clearance Sdruvss.
FL 370,
That was their assigned altitude and ATC NEVER CHANGED THAT ASSIGNED LEVEL. You cannot change altitude any time without expressed permission from ATC.
No matter how many times you ask the question you are not going to get the answer you are obviously looking for. The pilot you were talking to shortly after the accident was wrong. Or did not understand the circumstances.
FL 370,
That was their assigned altitude and ATC NEVER CHANGED THAT ASSIGNED LEVEL. You cannot change altitude any time without expressed permission from ATC.
No matter how many times you ask the question you are not going to get the answer you are obviously looking for. The pilot you were talking to shortly after the accident was wrong. Or did not understand the circumstances.
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Sdruvss : I fully support what con pilot just wrote. this is the way things works, not like your " pilot friend" said.
Also do not mix up a ' pre-departure clearance " that is a contract before take off that can be amended at any time once airborne by the controllers en route depending on other traffic.
To help you understand how things work, everywhere in the world , , let me try a small basic lecture if you allow me :
To stay in your country and in this case : Remember Brasilia VOR is an intersection of many airways. Therefore all kind of odds and even FLs are crossing there.(e.g. If 2 airways are facing west they are both using same family of levels )
Imagine there was another aircraft coming at FL 360 in the vicinity, from another airway, also heading for Brasilia VOR. Do you think that just because the airway direction changes for the Legacy, the controller is going to descent it and put it in conflict with that one ? Of course not. If nobody else is at FL370 ,he is going to wait some minutes before doing so. In the same manner , it is inconceivable for any pilot to just descend on his own to any level, when he overfly a VOR , just because its flight plan says so, as there might be other traffic in his vicinity at this level that is unaware of.
Under positive radar control, it is the controller that assign and determines the altitudes, not the pilot, and not the flight plan. The Flight plan is made of REQUESTED levels , as in " would like to have if available " levels. Those requested FLs have to be in line with what the AIP says, and for this route ( BRS-Manaus) it was even levels.
Therefore the flight plan said BRS FL360 and the controller last instruction was maintain FL370. both are perfectly correct in their own ways. The causes of the collision are not there, over BRS. They lie tens of minutes later.
Also do not mix up a ' pre-departure clearance " that is a contract before take off that can be amended at any time once airborne by the controllers en route depending on other traffic.
To help you understand how things work, everywhere in the world , , let me try a small basic lecture if you allow me :
To stay in your country and in this case : Remember Brasilia VOR is an intersection of many airways. Therefore all kind of odds and even FLs are crossing there.(e.g. If 2 airways are facing west they are both using same family of levels )
Imagine there was another aircraft coming at FL 360 in the vicinity, from another airway, also heading for Brasilia VOR. Do you think that just because the airway direction changes for the Legacy, the controller is going to descent it and put it in conflict with that one ? Of course not. If nobody else is at FL370 ,he is going to wait some minutes before doing so. In the same manner , it is inconceivable for any pilot to just descend on his own to any level, when he overfly a VOR , just because its flight plan says so, as there might be other traffic in his vicinity at this level that is unaware of.
Under positive radar control, it is the controller that assign and determines the altitudes, not the pilot, and not the flight plan. The Flight plan is made of REQUESTED levels , as in " would like to have if available " levels. Those requested FLs have to be in line with what the AIP says, and for this route ( BRS-Manaus) it was even levels.
Therefore the flight plan said BRS FL360 and the controller last instruction was maintain FL370. both are perfectly correct in their own ways. The causes of the collision are not there, over BRS. They lie tens of minutes later.
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Let´s accept this?
It seems to me that sdruvss is coming from a legal perspective and he wants the Legacy pilots to be held reponsible for the disaster. He is a fellow Brazilian that of course I respect.
But, let´s say that we agree with him: the Legacy pilots misunderstood ATC in São Jose and later did not notice that their transponder was off. So, in a situation like this Brazilian Traffic Controll allows a plane to fly in the wrong altitude, in a coliding route, for about ONE HOUR without trying to communicate with the pilots?...
I guess everyone flying in Brazil should then know that: if you are in a colision route, you are in your own...
Is this what Traffic Control is for?...
But, let´s say that we agree with him: the Legacy pilots misunderstood ATC in São Jose and later did not notice that their transponder was off. So, in a situation like this Brazilian Traffic Controll allows a plane to fly in the wrong altitude, in a coliding route, for about ONE HOUR without trying to communicate with the pilots?...
I guess everyone flying in Brazil should then know that: if you are in a colision route, you are in your own...
Is this what Traffic Control is for?...
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I think reporting in at FL370 and an acknowledgement of such is a confirmation that ATC accepts you at that altitude and therefore it is their responsibility to protect your altitude for your next segment of your flight.
No it was not. It was, I don't know the word in english, like a handshake. Controller was confirming that transponder was ok, confirming his altitude. This not mean that Brasilia to Manaus was cleared. This should be confirmed because it would be a flight plan change.
Others have tried (very capably in my opinion) to explain this.
A flight plan is just that. A booking, if you like, stating the requested routes and levels, among other things. At submission it is loaded in to the database.
It is nothing more (or less) than a tool for the controllers to use and refer to.
It should be considered as a strategic (planning) request, and as such, the levels (and other data entered) should comply with the rules for the route/s flown. This includes quadrantal altitude selection.
The actual business of controlling a flight will take all requests on the plan into account. In the initial clearance issued to the pilot, the clearance is to destination, via a particular route (usually flight planned route, but this can be changed according to traffic requirements and other reasons, such as a temporary restricted area) at the altitude requested initially on the plan. There is more to the clearance than just that, but those are the salient features.
Subsequent requests for altitude change, planned or not, for any reason, are handled by the controller/s handling the flight at the time the change is requested. This is the way it happens everywhere. And it is common. For example, many long distance flights file an initial cruise level somewhat below the level the pilot wishes to cruise at later, when fuel weight has been reduced, and a higher (and more efficient) level is planned for and requested, maybe 2 - 5 hours into the flight. This sort of request, planned or not, is handled at the time.
Ditto requests for direct routing, for which it is often not possible to file in the plan because of the route structure, but it is possible (sometimes) for the controller to approve at the time as workload and traffic and agreement of the subsequent sector/s allow.
Ditto requests to go around weather, which are (or should be) always approved, and the controller may take further steps (requesting a particular compass heading or altitude) if there are other aircraft in the way wanting to avoid the same weather. (Often the case.)
Sdruvss, if you wish to learn from this discussion, you need to understand the differences talked about here, between strategic planning (eg, a flight plan) and actual "hands on" tactical controlling (eg, making sure that flights are separated.)
If there were none of the former (flight plans) the system would not work because no controller would know who was entering the airspace next. If there was no tactical controlling, and instead, reliance was placed on every pilot exactly following their flight plans, a computer would have to calculate - before every takeoff - that those flights were all going to miss, and controllers wouldn't be required. (Technology is heading this way. At least for area control. Give it a few years.)
Nobody changes altitude just because that is what the flight plan has said, all things being normal, without a specific clearance to do so. Clearances are amended and modified all the time, throughout the course of a flight, according to the requirements of the flight crew, and ATC.
Get this, then you can start to talk about comm failure procedures, poor equipment design, poor displays of critical failures etc.
(To save you having to ask, or look it up, I am an ATCO, currently with a Tower (aerodrome) rating, with past area and radar ratings, and an approach rating. About 31 years service.)
(Some of us here may be prepared to accord you the respect you keep mentioning, if you were to state your occupation/experience/interest, etc, but quite frankly a great amount of respect has already been accorded. I'm quite impressed and a little humbled at the patience shown by many posters here.)
[Edit] (cross posted.)
and Legacy didn't know it was at level not cleared
That it appears ATC thought they were at another level is a very large part of the reason for the collision, probably the primary cause. I would expect the investigation to examine in detail the reasons as to why ATC thought they were at FL360, but their last cleared level was, I say again, FL370.