caos
au contraire mon ami
The Legacy was initially cleared to Manaus to maintain FL 370. No element of its clearance instructed it to do otherwise.
The controllers should have amended the clearance when 600XL checked-in just a few minutes prior to crossing BRS to either "cross BRS at and maintain 360" or "after BRS descend to and maintain 360' or just plain descend to and maintain 360". As previously noted, the obligation for 600XL to descend on its own to 360 materializes only after IT determines that a lost comm .situation exists.