I find it interesting that certain media sources are implying that the Legacy, flying at FL370 was at the incorrect altitude, when, in fact, following correct lost com procedures they were doing exactly the right thing, namely flying their last assigned route and flight level.
We also need to acknowledge that it is your last CLEARANCE that determines your route and altitude of flight, not your flight plan.
In the event of lost communications, you are expected to do the following in regards to your route of flight in the following order;
1.)Last Assigned route,
2.)Last assigned Heading if you were on radar vectors,
3.)What you were told to expect (ie, "in the event of lost comm, fly direct XXX and hold")
4.)Your Filed route.
In regards to Altitude you are expected to fly the HIGHEST of the following altitudes;
1.) The MEA for the airway
2.) The altitude you were told to Expect in your Last CLEARANCE.
3.) The last Assigned altitude given in your last communication.
Apply this to the lost comm situation the Legacy crew was allegedly experiencing and you do the following;
Fly your assigned route as per your last ATC Clearance
Fly your last assigned Altitude.
You DO NOT change altitudes after passing Brasilia, even though this was in your flight plan, as your last assigned altitude takes priority. The only exception to this would be if, in their last recieved ATC clearance they were told to,
"Maintain FL 370, at Brasilia VOR descend and maintain FL 360".
To my knowledge no such clearance was given.
Given the circumstances the Legacy crew were flying the correct altitude.