B757 PIC DECLARES 'PAN' PRIORITY FOR OFF RTE DIVERGENCE AND CLB AFTER ENCOUNTERING WX TURB. AFTER LNDG; ZOA ADVISES PLT OF INVESTIGATION FOR PLTDEV.

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APPROX 50 NM E OF ERWEN ON R577 AT FL380; ENCOUNTERED MODERATE TURB. WE MADE SURE THE CABIN CREW WAS SEATED AND REQUESTED AN ALT CHANGE FROM COMMERCIAL RADIO; AND WERE TOLD TO STAND BY. THE TURB INCREASED IN INTENSITY AND DUE TO PAX SAFETY CONCERNS WE MADE A 'PAN; PAN; PAN' CALL AND DEVIATED N OF TRACK R577. WE MADE ADVISORY CALLS DESCRIBING OUR SIT AND INTENTIONS ON 123.45 AND 121.5. WE OBTAINED CLRNC FROM COMMERCIAL RADIO TO DEVIATE 25 NM N OFF COURSE SHORTLY AFTER OUR INITIAL TURN OFF COURSE AND RECEIVED SUBSEQUENT CLRNCS TO CLB TO FL390 AND FL400. SHORTLY AFTER REACHING FL400; WE WERE TOLD TO CONTACT ZOA AFTER LNDG; FOR POSSIBLE PLT DEV. AFTER THE RIDE SMOOTHED TO AN ACCEPTABLE LEVEL WE RECEIVED CLRNC TO REJOIN R577 WHICH WE DID PRIOR TO ETNIC. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR ADVISED THAT THE THREAT TO FILE A DEV RPT DID NOT COME TO FRUITION. SUPPLEMENTAL INFO FROM ACN 600963: AFTER RPTING ERWEN INTXN EBOUND ON R577 AT FL380; ENCOUNTERED CONTINUOUS JOLTS OF MODERATE CLR AIR TURB INCREASING IN INTENSITY. SEATBELT SIGN WAS ON AND HAD FLT ATTENDANTS SUSPEND SVC/TAKE SEATS. RADAR WAS ALSO PAINTING PRESENCE OF CONVECTIVE WX ACTIVITY AHEAD AND ALONG TRACK. REQUESTED COMMERCIAL RADIO FOR ATC CLRNC TO OFFSET 25 NM N OF R577 AND REQUESTED CLB TO BLOCK FL390-FL400. A TIMELY RESPONSE WAS NOT RECEIVED FROM ATC. MEANWHILE; INTENSITY OF TURB WAS INCREASING AND PROX OF WX RETURNS WOULD SOON BE THREATENING SAFETY OF FLT. IN ACCORDANCE WITH INFLT CONTINGENCIES; PARAGRAPHS A-H OF THE PACIFIC OCEAN HIGH/LOW ALT ENRTE CHART 3/4; BROADCASTED PAN-PAN-PAN ON HF 5547; VHF 123.45 AND CHF 121.5; ADVISING COMMERCIAL RADIO AND ALL ACFT OF OUR INTENTION TO OFFSET 25 NM N OF R577. APPROX 10 NM N OF R577; RECEIVED ATC CLRNC TO OFFSET 25 NM N OF R577 AND CLRNC TO CLB TO FL390 UPON REACHING 25 NM N OF R577. RPTED ACHIEVING THE 25 NM OFFSET TO ATC AND INITIATED CLB TO FL390. CANCELED PREVIOUS REQUEST WITH ATC FOR CLRNC TO BLOCK FL390-FL400. AND REQUESTED CLRNC TO CLB TO MAINTAIN FL400. RECEIVED ATC CLRNC TO CLB TO FL400 AND RPTED REACHING. SUBSEQUENTLY; RECEIVED A SELCAL ADVISING ZOA WAS REQUESTING CAPT TO CALL ZOA; REF A 'POSSIBLE PLT DEV.' PRIOR TO REACHING ENGIN INTXN; TURB BEGAN MODERATING IN INTENSITY AND WX DEVS NO LONGER NECESSARY. REQUESTED ATC CLRNC TO REJOIN R577. RECEIVED ATC CLRNC TO REJOIN R577 PRIOR TO ETNIC INTXN. MADE A NORMAL POS RPT ABEAM ENGIN AT FL400 AND RPTED REINTERCEPTING R577 AT ETNIC INTXN. FLT LANDED LAX WITHOUT FURTHER INCIDENT OR PAX/CREW INJURY. AFTER LNDG; CAPT CALLED ZOA. WAS ADVISED THAT FAA INITIATING INVESTIGATION OF INCIDENT AS 'PLT DEV.' FAA ALLEGES ATC HAD NOT ISSUED THE CLRNC TO CLB TO FL390 PRIOR TO THEIR ISSUING A CLRNC TO CLB TO FL400.