Narrative:

Solid line of thunderstorms 30 degrees perpendicular to our track. Radar indicated best deviation to the left of track. Contacted radio on HF, requested '20 mi deviation to left off course due to cumulunimbus.' at that point we were approximately 110 NM east of line. Purser was advised that code 4 procedures would begin in 10 mins, lasting up to 20 mins. Purser advised me when cabin was prepared. Additional PA to passenger made from flight deck. 6 mins after request, radio advised that ATC denied our request for WX deviation. At that point, deviation to the right was impossible because of proximity of WX and turn radius at our TAS. I asked the first officer to concentrate on aircraft control and to follow headings I issued to deviate cells. Igniters and engine anti-ice were on. I asked the so to make additional PA reinforcing the need for passenger to remain seated. We deviated left off course approximately 12 mi to avoid level 5 thunderstorms with tops above FL400. We were unable to contact radio while IMC due to p-static associated with the thunderstorms. Appropriate WX deviation procedures (no radio communications) were instituted (air traffic control P-10). Notification to other aircraft was made on 121.5 and 123.45. Aircraft light on, TCASII on. When deviation exceeded 10 NM we descended to FL347. When deviation was completed, we returned to FL350 when within 10 mi of track. Maximum turbulence experienced was moderate.

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Original NASA ASRS Text

Title: B747-200 FLC ENCOUNTERS WX AND DEVIATES OFF ASSIGNED COURSE.

Narrative: SOLID LINE OF TSTMS 30 DEGS PERPENDICULAR TO OUR TRACK. RADAR INDICATED BEST DEV TO THE L OF TRACK. CONTACTED RADIO ON HF, REQUESTED '20 MI DEV TO L OFF COURSE DUE TO CUMULUNIMBUS.' AT THAT POINT WE WERE APPROX 110 NM E OF LINE. PURSER WAS ADVISED THAT CODE 4 PROCS WOULD BEGIN IN 10 MINS, LASTING UP TO 20 MINS. PURSER ADVISED ME WHEN CABIN WAS PREPARED. ADDITIONAL PA TO PAX MADE FROM FLT DECK. 6 MINS AFTER REQUEST, RADIO ADVISED THAT ATC DENIED OUR REQUEST FOR WX DEV. AT THAT POINT, DEV TO THE R WAS IMPOSSIBLE BECAUSE OF PROX OF WX AND TURN RADIUS AT OUR TAS. I ASKED THE FO TO CONCENTRATE ON ACFT CTL AND TO FOLLOW HEADINGS I ISSUED TO DEVIATE CELLS. IGNITERS AND ENG ANTI-ICE WERE ON. I ASKED THE SO TO MAKE ADDITIONAL PA REINFORCING THE NEED FOR PAX TO REMAIN SEATED. WE DEVIATED L OFF COURSE APPROX 12 MI TO AVOID LEVEL 5 TSTMS WITH TOPS ABOVE FL400. WE WERE UNABLE TO CONTACT RADIO WHILE IMC DUE TO P-STATIC ASSOCIATED WITH THE TSTMS. APPROPRIATE WX DEV PROCS (NO RADIO COMS) WERE INSTITUTED (AIR TFC CTL P-10). NOTIFICATION TO OTHER ACFT WAS MADE ON 121.5 AND 123.45. ACFT LIGHT ON, TCASII ON. WHEN DEV EXCEEDED 10 NM WE DSNDED TO FL347. WHEN DEV WAS COMPLETED, WE RETURNED TO FL350 WHEN WITHIN 10 MI OF TRACK. MAX TURB EXPERIENCED WAS MODERATE.

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.