doesn't the U/S RAD ALT only reduce the thrust if the aircraft is coupled up to an ILS?
Given it's a "full time" autothrottle on the Triple
AFAIK if serviceable it will close the thrust levers at 25 radio in a multitude of modes, not just G/S.
That said I'm still digging around in the manuals to find any dire warnings about the consequences of a single U/S rad alt on the 777 - are there any similarities between the 737 and 777 autothrottle logic or are comparisons with the AMS accident just a red herring??