As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
FLT#44, LGW-JFK. (ETOPS) 'ON TWO SEPERATE DESCENT LEGS THE AIRCRAFT DEPARTED THE FMS PATH AFTER APPROX 30S AND STARTED AN INCREASINGLY STEEP DESCENT WHILE IN A MANAGED DESCENT BOTH TIMES V/V EXCEEDED 4900 FPM AND THE AIRCRAFT WENT FROM FOLLOWING THE FMS PATH TO 1300FT BELOW IN A FEW SECONDS PITCH TRIM WAS NORMAL BOTH TIMES; REMOVED AND REPLACED FCU (2CA) PER MCC REQUEST IAW AMM 22-81-12-400-001-A OPS CHECK GOOD NO FAULT NOTED AT THIS TIME.'