What was found
WHILE IN CRUISE FL380 A SLIGHT BURNING SMELL BECAME PRESENT IN COCKPIT AND CABIN. SMELL QUICKLY BECAME VERY INTENSE IN CABIN AND COCKPIT. BOTH QRC AND QRH COMPLETED FOR SMOKE/FIRE OR FUMES. 02 MASKS CONT...DONNED SMELL DISSIPATED SHORTLY BEFORE LANDING AND DID NOT RETURN. NO VISIBLE SMOKE INDICATIONS WERE EVER PRESENT. NO 30DH - CH21/CH36<[01] PERFORMED IFIM TASK 21-00-00-810-830. REMOVED AND REPLACED L/H AND R/H RECIRCULATION AIR FILTERS PER AMM 21-25-01. OPS CHECK GOOD.;[02] PERFORMED IFIM TASK 21-00-00-810-830. REMOVED AND REPLACED L/H AND R/H RECIRCULATION AIR FILTERS PER AMM 21-25-01. OPS CHECK GOOD. C/W CONDITIONAL INSPECTION PER AMM 05-51-56; OKAY FOR SERVICE.