What was found
F/A REPORTED BURNING ODOR IN BACK OF AIRCRAFT AFTER TAKEOFF. AIR TURN BACK. NO INDICATIONS UP FRONT. INSPECTED AFT OF ACFT, NO BURNING ODOR NOTED. SUSPECT PRESERVATIVE OIL DUE TO 1ST FLT AFTER NR 2 ENGINE CHANGE, RAN BOTH ENGINES AND AIR SYS NO ODOR NOTED. REPLACED BOTH COALESCER BAGS, MM 21-54-08. OPS CHECKED GOOD.