GPS approaches

[aliform]

I am tasked with 'finding-out' about stand-alone GPS approaches, and Overlays. Having read the JAA leaflet with all its requirements, I still need to know how operators do these. (Boeing's procedures ar eno real help.) Presumably using the FMS in Lnav, Vnav with the RNP as accuracy verification.
Does anyone have any information?
Also which operators are currently approved?

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Heavenly Dancer

[cossack]

US Air are approved to do an LNAV/VNAV approach on their A330-300s into LGW and soon MAN.
Sorry can't help with the "technicalities" though.

[Intruder]

Overlay approaches (VOR/NDB approaches following the same track as a GPS approach) are usually flown in LNAV for horizontal guidance, and either VNAV or V/S for vertical guidance. Autopilot, flight director, and autothrottle use is up to the Captain.

FAA-approved Operational Specifications (OpSpecs) for individual US-certificated airlines may dictate whether or not "pure" GPS approaches may be flown, and whether or not VNAV is approved for use on the final approach segment.