What was found
SMOKE AND FUMES IN FLIGHT DECK AND CABIN. ENGINE DISASSEMBLY VERIFIED A BAD NR 2&3 CARBON SEAL. WHEN THIS CARBON SEAL LEAKS, PRESSURE BUILDS UP IN THE NR 1&3 AFT COMPARTMENT. EXCESSIVE PRESSURE ALLOWS OIL TO SEEP PAST AND THOSE SEALS AND ALLOWING BURNING OIL TO ENTER THE BLEED SYSTEM, WHICH FEEDS AIR TO THE CABIN. THE NR 2&3 CARBON SEAL IS A KNOWN PROBLEM THAT IS SYSTEMIC TO THE FLEET. ENGINES MODIFIED WITH A NEW DESIGN NR 2&3 CARBON SEAL WILL ELIMINATE THIS FAILURE MODE.