As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
UPON APPROACH TO GC902 DURING BEFORE LANDING CHECK, GEAR WOULD NOT EXTEND. RETURNED TO HUM AND USED EMERGENCY BLOW DOWN. TROUBLESHOOTING REVEALED CONTACTS BETWEEN PINS A AND B OF LANDING GEAR CONTROL PANEL MAINTAINING CONTINUITY WHEN GEAR LEVER IS PLACED IN THE DOWN POSITION. THEREFORE POWER IS CONTINUALLY SUPPLIED TO THE RETRACT SIDE OF THE CONTROL VLAVE.