Narrative:

The captain and I were air carrier flight X en route to ord from sfo at FL330. We requested FL370 to avoid an area of severe WX approximately 60-70 mi ahead. Our radar indicated at least level 4 echoes. Turbulence became light to moderate. ATC stated unable for traffic and we could not expect higher for at least 8 mins. We then requested deviations left of course. ATC asked if we could go right and we replied unable for the WX and needed to go left. At this time it was then too dangerous to continue straight ahead. The captain turned approximately 20 degrees left of course to assure safety of flight. We advised ATC of course deviation. ATC stated he needed us back on course for descending traffic (air carrier Y) to the north. When it was safest to turn back we advised ATC we were doing so. ATC replied we turned without clearance and that he had descending air carrier Y traffic to the north. Our flight and air carrier Y never came within 5 mi of each other. Our thoughts are ATC could have prioritized which flight needs clearance according to safety of flight. Air carrier X needed deviation off course to prevent encounter with severe WX, but was unable to do so from ATC because an air carrier Y flight was descending. Severe WX was not an issue for air carrier Y. Some corrective action could have been giving other clearance to air carrier Y to help us remain clear of severe WX and assure the safety of our flight. Supplemental information from acn 472430: I know that traffic separation is extremely important. So is keeping my aircraft, passenger and crew out of thunderstorm tops. Perhaps in the future, when not given permission to turn to avoid a thunderstorm, I will immediately declare an emergency.

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Original NASA ASRS Text

Title: WX AVOIDANCE CAUSES AIR TFC PROBS.

Narrative: THE CAPT AND I WERE ACR FLT X ENRTE TO ORD FROM SFO AT FL330. WE REQUESTED FL370 TO AVOID AN AREA OF SEVERE WX APPROX 60-70 MI AHEAD. OUR RADAR INDICATED AT LEAST LEVEL 4 ECHOES. TURB BECAME LIGHT TO MODERATE. ATC STATED UNABLE FOR TFC AND WE COULD NOT EXPECT HIGHER FOR AT LEAST 8 MINS. WE THEN REQUESTED DEVS L OF COURSE. ATC ASKED IF WE COULD GO R AND WE REPLIED UNABLE FOR THE WX AND NEEDED TO GO L. AT THIS TIME IT WAS THEN TOO DANGEROUS TO CONTINUE STRAIGHT AHEAD. THE CAPT TURNED APPROX 20 DEGS L OF COURSE TO ASSURE SAFETY OF FLT. WE ADVISED ATC OF COURSE DEV. ATC STATED HE NEEDED US BACK ON COURSE FOR DSNDING TFC (ACR Y) TO THE N. WHEN IT WAS SAFEST TO TURN BACK WE ADVISED ATC WE WERE DOING SO. ATC REPLIED WE TURNED WITHOUT CLRNC AND THAT HE HAD DSNDING ACR Y TFC TO THE N. OUR FLT AND ACR Y NEVER CAME WITHIN 5 MI OF EACH OTHER. OUR THOUGHTS ARE ATC COULD HAVE PRIORITIZED WHICH FLT NEEDS CLRNC ACCORDING TO SAFETY OF FLT. ACR X NEEDED DEV OFF COURSE TO PREVENT ENCOUNTER WITH SEVERE WX, BUT WAS UNABLE TO DO SO FROM ATC BECAUSE AN ACR Y FLT WAS DSNDING. SEVERE WX WAS NOT AN ISSUE FOR ACR Y. SOME CORRECTIVE ACTION COULD HAVE BEEN GIVING OTHER CLRNC TO ACR Y TO HELP US REMAIN CLR OF SEVERE WX AND ASSURE THE SAFETY OF OUR FLT. SUPPLEMENTAL INFO FROM ACN 472430: I KNOW THAT TFC SEPARATION IS EXTREMELY IMPORTANT. SO IS KEEPING MY ACFT, PAX AND CREW OUT OF TSTM TOPS. PERHAPS IN THE FUTURE, WHEN NOT GIVEN PERMISSION TO TURN TO AVOID A TSTM, I WILL IMMEDIATELY DECLARE AN EMER.

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.