A B777 EICAS alerted R BODY BLEED LOSS. The crew was unable to determine the exact nature of the loss and so diverted to an enroute airport as a precaution.

Narrative

I came up to the cockpit after my break approximately 3.5 hours into the flight. Captain and First Officer were working a problem with the pressurization system. Aircraft was dispatched with a couple of problems with the left Air Conditioning/Pressurization System (HPSOV MEL and Trim Air MEL). Captain and First Officer were working a new problem: Right Body Bleed Loss. When I got to the cockpit the Captain had already initiated a conversation with Maintenance and Dispatch. The synoptic did not indicate whether or not the left isolation valve had closed; and this was causing the Captain some consternation as he was concerned as to exactly where that bleed air was leaking. Maintenance was not able to provide a satisfactory answer; so the Captain decided upon the most conservative course of action and turned off the Right Bleed and descended to FL250. We were in radar and radio contact so this was quickly approved. We were discussing the situation and I offered the opinion that we should not be using the synoptic presentation to diagnose problems with the air conditioning. The suggestion was also preferred that there is no altitude restriction for single pack operation with this aircraft. The Captain considered both points and decided that FL250 was the most prudent course of action. We crossed at 250; received revised clearance to an en route airport and proceeded uneventfully. It should be noted that while we were on approach; we received several EICAS and STATUS messages all relating to both Air Conditioning/Pressure System (i.e. Outflow Valve Left; Outflow Valve Right; etc.)