Technician reported a fuel spill during an ETOPS Pre Departure Check when the aircraft fueler began fueling while technicians were cross feeding fuel to correct a fuel imbalance.

Report 1 | Narrative: We started our preflight ETOPS Pre-Departure Check of Aircraft X. Woke plane up and noticed aircraft had a Fuel Auto Transfer fault and we noticed 5;000 pounds in center tank. Wings were approx. 10;000 pounds. Per Company Manual XX-XX-XX-XXX-XXXA needed to move fuel center tank to wing tanks. while transferring fuel from center tanks to wing tanks per AMM (Aircraft Maintenance Manual) XX-XX-XX-XXX-XXXA paragraph X fault extinguished. Fuel transferred from 5;000 pounds to 800 pounds. At 800 pounds; fuel jumped to approximately 2;000 pounds and a fuel overflow message on the R/H wing. Shut off fuel pumps and stopped transferring operations.

Fuel load on flight plan 36;000 pounds. Current fuel load on aircraft 30;000 pounds fuel density was 6.58 RH wing vent box fuel spill. Previous start up messages on fuel system. Fueler fueled during fuel transfer. Fuel door was open. Fuel indicators reflected fuel transfer. Fueler didn't notice fuel transfer approaching max wing tank capacity. Fueler didn't notice transfer in progress while setting fuel load prior to fueling A/C. Shut down fuel transferring procedures and cleaned up fuel spill.

Report 1 | Synopsis: Technician reported a fuel spill during an ETOPS Pre Departure Check when the aircraft fueler began fueling while technicians were cross feeding fuel to correct a fuel imbalance.