I read with interest the posts about RVSM being discontinued due to in-flight transponder failure. The US does not discontinue RVSM due to transponder failure. I'm curious about ICAO. Is is country specific? I've searched the online ICAO resources and cannot find a concrete answer on in-flight failures.
It will depend on what is in the ICAO Regional Supplementary for the airspace involved. Most have adopted the European procedures, but I can't confirm if that is also the case for Brasil. Some States in Europe allow continued RVSM flight without a transponder, some don't. I'd imagine it is a similar story in other ICAO regions.
European MELs for RVSM flight are in JAA TGL 6, with further clarification on the Eurocontrol RVSM FAQ page.
8.1 Equipment for RVSM Operations
The minimum equipment fit is:
8.1.1 Two independent altitude measurement systems.
8.1.2 One secondary surveillance radar transponder with an altitude reporting system that can be connected to the altitude measurement system in use for altitude keeping.
8.1.3 An altitude alerting system.
8.1.4 An automatic altitude control system.
Source: TGL6
The ICAO RVSM requirements do not preclude ATC clearance into European RVSM airspace for RVSM-approved aircraft and non-RVSM approved State aircraft that experience Mode C transponder failure (or if the Mode C readout is misreading by more than 200 feet) prior to intended entry into RVSM airspace.
However, the specific requirement for the carriage and operation of transponders is a "State" responsibility, in accordance with �Annex 11 to the Convention on International Civil Aviation�, Chapter 2, paragraph 2.25, which reads as follows:
"States shall establish requirements for carriage and operation of pressure-altitude reporting transponders within defined portions of airspace".
Please refer to relevant National Aeronautical Information Publications (AIPs) for information on transponder requirements.
Source: Eurocontrol