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Each country's civil aviation authority determines whether to authorise GNSS approaches, for example this could be DGAC France, CAA UK, FAA USA.
The CAA UK has recently authorised non precision GNSS approaches.
Information on the UK requirements can be obtained from
http://www.caa.co.uk/docs/33/20070704ATS108.pdf
The document mentions "suitably equipped aircraft". This will normally mean that the aircraft is equipped with a Multi Mode Receiver (MMR) which will permit reception of GPS and interface into the aircraft's navigation system. Most new commercial aircraft are now equipped with MMR, including Airbus, Boeing and Embraer.
OACI/ICAO does not certify aircraft or GNSS approaches, it publishes the international requirements for them. Each ICAO Contracting State, for example France/UK/USA, then determines whether to accept the ICAO requirements and then publishes it's requirements via their civil aviation authority.
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