Narrative:

On initial application of takeoff thrust; a slight thump was felt in the cockpit; akin to running over a hole in the runway. As all cockpit indications appeared normal; we continued the takeoff. Departure through 7000 ft was uneventful. Passing about 7000 ft for 10000 ft; we noticed a lack of cockpit air conditioning flow and warm cockpit temperature. At 10000 ft; we monitored the air conditioning maintenance display page. Temperatures throughout the aircraft were in the mid 80's; and the cockpit temperature was 93 degrees. Pressurization and all other indications appeared normal. We established communication with maintenance; but even with their assistance we could not determine cause. The cockpit temperature was now 95 degrees. I decided to return to ZZZ and notified flight control. Aircraft gross weight was 385000 pounds; with 16000 pounds in the center tanks. I decided to dump fuel during return. When center tanks were emptied; aircraft gross weight was 368000 pounds. I decided to exercise emergency authority/authorized and land overweight. I did not declare an emergency after considering aircraft confign; visibility; runway conditions and familiarity with the field. After landing and taxi to gate; a logbook entry for overweight landing was made. The thump turned out to be cargo pallet contacting rear bulkhead of forward cargo bin; which interrupted air conditioning to aircraft cabin.

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Original NASA ASRS Text

Title: UNABLE TO COOL THE AIRCRAFT AFTER TAKE OFF; B767-400 RETURNS TO DEPARTURE AIRPORT. MAINTENANCE DETERMINES AN UNSECURED CARGO PALLET ROLLED AFT ON TAKE OFF AND ITS IMPACT WITH THE AFT BULKHEAD RENDERED TEMPERATURE CONTROL INOPERABLE.

Narrative: ON INITIAL APPLICATION OF TKOF THRUST; A SLIGHT THUMP WAS FELT IN THE COCKPIT; AKIN TO RUNNING OVER A HOLE IN THE RWY. AS ALL COCKPIT INDICATIONS APPEARED NORMAL; WE CONTINUED THE TKOF. DEP THROUGH 7000 FT WAS UNEVENTFUL. PASSING ABOUT 7000 FT FOR 10000 FT; WE NOTICED A LACK OF COCKPIT AIR CONDITIONING FLOW AND WARM COCKPIT TEMP. AT 10000 FT; WE MONITORED THE AIR CONDITIONING MAINT DISPLAY PAGE. TEMPS THROUGHOUT THE ACFT WERE IN THE MID 80'S; AND THE COCKPIT TEMP WAS 93 DEGS. PRESSURIZATION AND ALL OTHER INDICATIONS APPEARED NORMAL. WE ESTABLISHED COM WITH MAINT; BUT EVEN WITH THEIR ASSISTANCE WE COULD NOT DETERMINE CAUSE. THE COCKPIT TEMP WAS NOW 95 DEGS. I DECIDED TO RETURN TO ZZZ AND NOTIFIED FLT CTL. ACFT GROSS WT WAS 385000 LBS; WITH 16000 LBS IN THE CTR TANKS. I DECIDED TO DUMP FUEL DURING RETURN. WHEN CTR TANKS WERE EMPTIED; ACFT GROSS WT WAS 368000 LBS. I DECIDED TO EXERCISE EMER AUTH AND LAND OVERWT. I DID NOT DECLARE AN EMER AFTER CONSIDERING ACFT CONFIGN; VISIBILITY; RWY CONDITIONS AND FAMILIARITY WITH THE FIELD. AFTER LNDG AND TAXI TO GATE; A LOGBOOK ENTRY FOR OVERWT LNDG WAS MADE. THE THUMP TURNED OUT TO BE CARGO PALLET CONTACTING REAR BULKHEAD OF FORWARD CARGO BIN; WHICH INTERRUPTED AIR CONDITIONING TO ACFT CABIN.

Data retrieved from NASA's ASRS site as of May 2009 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.