As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
LHR - CREW REPORTED SEAT 3G ARMREST STARTED TO SMOKE AND LUMBAR SEEMED TO BE VIBRATING ON LANDING. FOUND ARMREST CONTROL PAD WITH STRONG ELECTRICAL SMELL. REPLACED CONTROL PAD. NO OBVIOUS DAMAGE TO WIRING. SYSTEM GROUND CHECK NORMAL OPERATION.