Narrative:

Preflight briefing gave no indications of significant turbulence other than some light turbulence over east central europe. After crossing 2/3 across north atlantic, wbound, we began hearing other aircraft to aircraft reports of moderate to severe turbulence at all altitudes from FL410 down to FL280 approximately 200 mi ahead of our position. These reports were coming from all the tracks. HF radio communication was unobtainable by any aircraft, including ourselves. As we neared the north american coast, intermittent VHF communication were beginning to be received, however the frequency was swamped, with some position reports 45 mins old. No one requesting altitude or flight plan changes were being obtained. It became obvious we could not avoid the area of turbulence ahead vertically or laterally and, of course, had insufficient fuel to return anywhere eastbound. We prepared the passenger, flight attendants, and cabin for moderate or greater turbulence, and slowed our speed. An aircraft on our track, 2000 ft above slowed more than us and we gradually flew beneath. An aircraft on our track 1000 ft below rapidly gained and flew beneath us. Winds were at 172 KTS and began subsiding to 117 KTS followed by an increase back to 168 KTS with light to moderate turbulence. Approximately 60 mi east of area of moderate to severe reports of turbulence, we encounter severe turbulence at FL340. Nose pitched up, followed by a 30 degree left roll, nose fell, stick-shaker accompanied by buffeting, TCASII RA climb. Altitude varied from FL341 to FL336. Aircraft 2000 ft above us approximately 3/4 mi ahead, however aircraft 1000 ft below was directly beneath on TCASII. Recovery to a climb to FL340 and roll correction right was made and immediately broke out right off track to exit this sandwich. Strongly recommend oceanic traffic with only 1000 ft separation be assigned left track, on track and right track separation.

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Original NASA ASRS Text

Title: FLT CREW OF B762 ENCOUNTER SEVERE TURB OVER THE NORTH ATLANTIC IN RVSM AIRSPACE. ALTDEVS WHICH RESULT CAUSE A TCASII RA WITH ACFT 1000 FT BELOW.

Narrative: PREFLT BRIEFING GAVE NO INDICATIONS OF SIGNIFICANT TURB OTHER THAN SOME LIGHT TURB OVER EAST CENTRAL EUROPE. AFTER XING 2/3 ACROSS NORTH ATLANTIC, WBOUND, WE BEGAN HEARING OTHER ACFT TO ACFT RPTS OF MODERATE TO SEVERE TURB AT ALL ALTS FROM FL410 DOWN TO FL280 APPROX 200 MI AHEAD OF OUR POS. THESE RPTS WERE COMING FROM ALL THE TRACKS. HF RADIO COM WAS UNOBTAINABLE BY ANY ACFT, INCLUDING OURSELVES. AS WE NEARED THE NORTH AMERICAN COAST, INTERMITTENT VHF COM WERE BEGINNING TO BE RECEIVED, HOWEVER THE FREQ WAS SWAMPED, WITH SOME POS RPTS 45 MINS OLD. NO ONE REQUESTING ALT OR FLT PLAN CHANGES WERE BEING OBTAINED. IT BECAME OBVIOUS WE COULD NOT AVOID THE AREA OF TURB AHEAD VERTLY OR LATERALLY AND, OF COURSE, HAD INSUFFICIENT FUEL TO RETURN ANYWHERE EBOUND. WE PREPARED THE PAX, FLT ATTENDANTS, AND CABIN FOR MODERATE OR GREATER TURB, AND SLOWED OUR SPD. AN ACFT ON OUR TRACK, 2000 FT ABOVE SLOWED MORE THAN US AND WE GRADUALLY FLEW BENEATH. AN ACFT ON OUR TRACK 1000 FT BELOW RAPIDLY GAINED AND FLEW BENEATH US. WINDS WERE AT 172 KTS AND BEGAN SUBSIDING TO 117 KTS FOLLOWED BY AN INCREASE BACK TO 168 KTS WITH LIGHT TO MODERATE TURB. APPROX 60 MI E OF AREA OF MODERATE TO SEVERE RPTS OF TURB, WE ENCOUNTER SEVERE TURB AT FL340. NOSE PITCHED UP, FOLLOWED BY A 30 DEG L ROLL, NOSE FELL, STICK-SHAKER ACCOMPANIED BY BUFFETING, TCASII RA CLB. ALT VARIED FROM FL341 TO FL336. ACFT 2000 FT ABOVE US APPROX 3/4 MI AHEAD, HOWEVER ACFT 1000 FT BELOW WAS DIRECTLY BENEATH ON TCASII. RECOVERY TO A CLB TO FL340 AND ROLL CORRECTION R WAS MADE AND IMMEDIATELY BROKE OUT R OFF TRACK TO EXIT THIS SANDWICH. STRONGLY RECOMMEND OCEANIC TFC WITH ONLY 1000 FT SEPARATION BE ASSIGNED L TRACK, ON TRACK AND R TRACK SEPARATION.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.