Aviadornovato :
many points in your post above deserving long answers, but due to lack of time , I will only take the first one :
you said :
I proposed adherence to Flight Plans on the grounds that airways should have predefined FLs between waypoints in order to avoid collisions and also predefined rules on FL in case of lost communication. So a clearance that didn’t adhere to a filed flight plan would have to be avoided IMHO.
That is a correct assumption if we were talking about Procedural control, i.e not radar control. In a radar control environment the minimum separation criteria is 5NM or 1000 ft. How to achieve this is dynamic, and flexible ( i.e. radar vectoring, anticipating or delaying planned climbs or descents, etc.. ) Therefore in radar control airspace you can ( and many do ) use all the altitudes at your disposition regardless of Flight plan or predefined altitudes on the airways or tracks.
Radar control also imply full 2 way radio telephony capability at all times.
So if we were in a full radar environment the clearances issued by the Brasilia Controllers were not abnormal, nor " wrong ". The problem lies in the fact that , in our case, both radar and VHF communications were lost.
Now, and there it is my own interpretation : As far as I can see, in CINDACTA 1 , for whatever reason ( having to do perhaps with national pride or for hiding the fact that the military are not being able to cover the whole Amazonas ) is providing radar service and separation in deficient areas. We learned that there are large areas declared " radar area" which in fact are areas of poor or no VHF radio coverage and no civil radar coverage.
In those areas , procedural control should have been in place , i.e altitude separation and 10 minutes between aircraft.
Procedural control is totally different from Radar and need different training. We are not sure that the staff in CINDACTA 1 are procedurally trained.
Comm failures :
We have not been able to asses yet which procedure apply in Brazil in case of radio communication failure : the US one or the worldwide ICAO one .
Now about your statement that the system was showing the right Flight level, this is incorrect ,and is part of the main cause of this accident . Nobody willingly “ forgets “ an aircraft or the level at which it is in reality. A combination of technical and human factors led someone to believe that the Legacy was 1000 Ft higher that in was in reality.
Eliminating that from happening again is the issue. Looking for controllers or pilot “errors” will only delay the corrections that will prevent another accident.
One thing is for sure, if the system is not changed, it is only a matter of time until you have another accident.