As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
UNKNOWN BURNING SMELL DETECTED IN FLIGHT DECK AND CABIN IN CRUISE FLIGHT, WENT AWAY AFTER 3 MINUTES LATER. INSPECTED FLIGHT DECK AND CABIN FOR POSSIBLE DEFECTS. NONE FOUND. BOTH ENGINES RUN UP AND BLEEDS SELECTED FOR BOTH ENGINES. RAN BOTH AC PACKS AND APU BLEEDS. NO BURNING ODER DETECTED. AC OK FOR SERVICE IAW 21-00-00-02.