Narrative:

Air carrier X requested deviation 20 NM east of L455 due to weather. [I] advised flight unable left deviation due to traffic; right deviation available. Air carrier X was boxed in vertically by aircraft at FL380 and FL360. Air carrier Y was the air carrier X's traffic on L456 approximately 50 NM away to the east and air carrier Y was unable higher for at least another 1/2 hour and I was unable to issue decent clearance due to northbound traffic for air carrier Y. Air carrier X advised he was declaring a weather emergency and going 40 NM left of L455. I advised air carrier X of air carrier Y's prhca estimate and altitude. I advised air carrier Y that air carrier X was deviating without a clearance and advised air carrier Y of air carrier X's macor estimate and altitude. Air carrier X reported air carrier Y 'in sight'. As far as I know air carrier Y never saw air carrier X and according to atop; air carrier Y was behind air carrier X. After air carrier X finished deviating I asked flight for a PIREP. Flight described a bad thunderstorm; no mention of turbulence. I also asked a flight on same route at FL350 their flight conditions; they said IMC; moderate chop; aircraft did not deviate at all. This flight was only about 10 minutes in trail to air carrier X. Nothing could have prevented this. The last 5-6 aircraft had flown directly through this weather and there was little room to move other aircraft. Air carrier X could have deviated all they wanted to the right; but insisted on going left; into traffic.

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Original NASA ASRS Text

Title: ZNY Controller and flight crew described a loss of separation event involving oceanic traffic requesting a weather deviation; directed by ATC to deviate right but elected to turn left to avoid weather.

Narrative: Air Carrier X requested deviation 20 NM east of L455 due to weather. [I] advised flight unable left deviation due to traffic; right deviation available. Air Carrier X was boxed in vertically by aircraft at FL380 and FL360. Air Carrier Y was the Air Carrier X's traffic on L456 approximately 50 NM away to the east and Air Carrier Y was unable higher for at least another 1/2 hour and I was unable to issue decent clearance due to northbound traffic for Air Carrier Y. Air Carrier X advised he was declaring a weather emergency and going 40 NM left of L455. I advised Air Carrier X of Air Carrier Y's PRHCA estimate and altitude. I advised Air Carrier Y that Air Carrier X was deviating without a clearance and advised Air Carrier Y of Air Carrier X's MACOR estimate and altitude. Air Carrier X reported Air Carrier Y 'In Sight'. As far as I know Air Carrier Y never saw Air Carrier X and according to ATOP; Air Carrier Y was behind Air Carrier X. After Air Carrier X finished deviating I asked flight for a PIREP. Flight described a bad thunderstorm; no mention of turbulence. I also asked a flight on same route at FL350 their flight conditions; they said IMC; moderate chop; aircraft did not deviate at all. This flight was only about 10 minutes in trail to Air Carrier X. Nothing could have prevented this. The last 5-6 aircraft had flown directly through this weather and there was little room to move other aircraft. Air Carrier X could have deviated all they wanted to the right; but insisted on going left; into traffic.

Data retrieved from NASA's ASRS site as of April 2012 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.