As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
THE NOSE GEAR RETRACTED DURING ENGINE START WITH THE GEAR SELECTOR DOWN AND THREE GREEN GEAR IND LIGHTS. INVESTIGATION FOUND THE LEFT DOWNLOCK SWITCH FAILED IN THE CONTROL CIRCUIT APPLYING POWER TO THE LOADING VALVE AND HYD SLECTOR VALVE. PIN B AND D IN CONNECTOR P52 WERE FOUND REVERSED. SL PJ81-15 WAS C/W.