ICA 100-12
RULES OF THE AIR AND SERVICES OF AIR TRAFFIC 2006
(Brazilian Rules)
7.14 FLAW OF LAND AND AIR COMMUNICATIONS
7.14.1 when the organs ATC could not maintain bilateral communication with an aircraft in flight, they should take the following measures:
a) to verify the aircraft can receive the transmissions of the organ, asking him/her that it executes specific maneuvers that you/they can be observed in the presentation radar or that it transmits, if possible, a specified sign with the purpose of accusing the reception of the message; and
b) if the aircraft nothing to accuse, the controller should maintain the separation among the aircraft with communication flaw and the others, supposing that the aircraft will adopt the established procedures for flaw of communications.
Source: http://www.clubeceu.com.br/download/ICA_100-12.pdf in portuguese.
Unfortunately the web site of the DAC (Address of Civil Aeronautics) it is "under construction" and the rules cannot be obtained in English.