As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
ETOPS SIGNIFICANT SYS - ON TAKEOFF AFTER GEAR RETRACTION, EICAS MESSAGE "GEAR NOT DOWN" AND MASTER WARNING ACTIVATED. LASTED FOR 5 SECONDS. T/S IAW FIM 31-51-00/101, FIG 109A. COMPLIED WITH BLOCKS 1,2,3 AND 33. NO PROBLEMS FOUND DURING TROUBLESHOOTING.