As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
STRONG SMELL OF PLASTIC BURNING JUST AFTER TAKEOFF. UPON ARRIVAL DEBRIEFED CREW AND FOUND SMELL HAD DISSIPATED BEFORE RETURN TO EWR. PERFORMED IMMEDIATE INSPECTION OF LP PLENUM ( WHERE GROUND AIR CONDITION HOOKS UP) FOUND NO OIL RESIDUE. PERFORMED FIMTASK 21-00-00-810-806. ALSO RAN ENGINES AT T/O POWER FOR 5 MIN BLEEDS OFF, 5 MIN BLEEDS ON, 5 MIN WITH PACKS ON. NO SMELL.