Narrative:

At approximately the time and location listed above, a descent from FL390 to FL330 was initiated due to a steadily declining fuel temperature which was approaching the limits listed in the C-141B operations specifications. Gander advised of traffic eastbound at FL370 and FL350, and repeatedly denied our descent requests. As the fuel temperature dropped to a critically low level, we offset 30 NM north of track and began a descent to FL330 without clearance from gander to avoid a potentially hazardous situation. We relayed our progress throughout the offset, descent, level off, and return to course to gander. Gander had no reported traffic at FL330. Shortly after level off, radar contact was established with reykjavik control. The need for a descent for operational necessity was discussed with gander for at least 20 mins prior to the initiation of our descent. When the fuel temperature fell to -40 degrees C, we as a crew felt it necessary to immediately begin a descent to warmer temperature in the interest of safety. After level off at FL330, it was determined that the temperature in the #1 main tank was -45 degrees C at the time of descent. The freeze point of JP5 is -46 degrees C. Later, under radar control and with clearance, another descent to FL290 had to be initiated to control the fuel temperature.

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Original NASA ASRS Text

Title: OCEANIC MIL FLT IN VERY COLD TEMPS, FUEL TEMP WAS GETTING CLOSE TO CRITICAL (FREEZING), BUT DUE TO CONFLICTING TFC AT LOWER ALT, ATC WAS UNABLE TO CLR RPTR ACFT TO LOWER (WARMER) ALT. BECAUSE OF CRITICAL TEMP, FLC DIVERTED 30 MI OFF COURSE AND DSNDED WITHOUT CLRNC.

Narrative: AT APPROX THE TIME AND LOCATION LISTED ABOVE, A DSCNT FROM FL390 TO FL330 WAS INITIATED DUE TO A STEADILY DECLINING FUEL TEMP WHICH WAS APCHING THE LIMITS LISTED IN THE C-141B OPS SPECS. GANDER ADVISED OF TFC EBOUND AT FL370 AND FL350, AND REPEATEDLY DENIED OUR DSCNT REQUESTS. AS THE FUEL TEMP DROPPED TO A CRITICALLY LOW LEVEL, WE OFFSET 30 NM N OF TRACK AND BEGAN A DSCNT TO FL330 WITHOUT CLRNC FROM GANDER TO AVOID A POTENTIALLY HAZARDOUS SIT. WE RELAYED OUR PROGRESS THROUGHOUT THE OFFSET, DSCNT, LEVEL OFF, AND RETURN TO COURSE TO GANDER. GANDER HAD NO RPTED TFC AT FL330. SHORTLY AFTER LEVEL OFF, RADAR CONTACT WAS ESTABLISHED WITH REYKJAVIK CTL. THE NEED FOR A DSCNT FOR OPERATIONAL NECESSITY WAS DISCUSSED WITH GANDER FOR AT LEAST 20 MINS PRIOR TO THE INITIATION OF OUR DSCNT. WHEN THE FUEL TEMP FELL TO -40 DEGS C, WE AS A CREW FELT IT NECESSARY TO IMMEDIATELY BEGIN A DSCNT TO WARMER TEMP IN THE INTEREST OF SAFETY. AFTER LEVEL OFF AT FL330, IT WAS DETERMINED THAT THE TEMP IN THE #1 MAIN TANK WAS -45 DEGS C AT THE TIME OF DSCNT. THE FREEZE POINT OF JP5 IS -46 DEGS C. LATER, UNDER RADAR CTL AND WITH CLRNC, ANOTHER DSCNT TO FL290 HAD TO BE INITIATED TO CTL THE FUEL TEMP.

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.