Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument
Aircraft Equipment Problem Less Severe; Conflict Airborne Conflict
Aircraft
I was Pilot Flying; Captain was Pilot Monitoring; and First Officer was resting. Notable weather was intermittent light turbulence; and undercast. Near [coordinates] on NAT F; we were being passed by [another air carrier]; 1000 FT below. We were on a 2M SLOP and they appeared to be on a 1M SLOP. After a few TAs; with them in sight; we received an RA; essentially telling us to stay level. We observed them by visual reference and TCAS to be turning left (away; towards the track) and descending. Contact with [other air carrier] on [frequency] confirmed that they would stay on track while passing us. We communicated the incident with ATC via HF; and confirmed our position; route; SLOP; and altitude. A notable factor was some irregularities we observed with the L Altimeter; namely that it was more erratic than normal / the R Altimeter; meaning that it deviated more (about our cruise altitude) in anything but smooth air (+/- 40' in light; and +/- 80' in moderate). Additionally; the two altimeters were near the 200 FT RVSM limit (180-200 FT). In fact; we did later get an ALT DISAGREE EICAS message. For that; we completed the QRH; consulted the Flight Operations Manual; and made a logbook entry.
Air carrier First Officer reported receiving a RA in RVSM airspace.  The pilot stated the aircraft's altimeters were off by 180 feet.