What do you mean? How ATC will help us without our FL?
(Sorry but are you a real pilot?)
Yes, I am a pilot with over 30 years experience in every part of the world except Africa.
On first contact, the primary way for an air traffic controller to establish the altitude of an aircraft is at is to simply ask him on the radio. He then takes a pen and checks off a little strip of paper to verify he is at the correct altitude.
If there is no contact, then the aircraft is at the last cleared altitude that was received and acknowledged by the pilot.
This is universal all over the world.
This is what failed in Brazil.