SMT ACFT HAS NOSE GEAR RETRACT AS ENG STARTED. PROP STRIKES GND.

Narrative

DURING START OF THE R ENG (THE FIRST TO BE STARTED) THE NOSE GEAR RETRACTED CAUSING THE R PROP TO STRIKE THE GND AND STOP. DURING THE PREFLT I OBSERVED THE MAIN GEAR DOORS OPEN. MAINT HAD INSPECTED AND WASHED THE ACFT DURING THE NIGHT SHIFT. I KNEW THAT THE DOORS WOULD CLOSE WHEN THE GEAR HANDLE WAS PLACED DOWN WITH THE ENGS RUNNING. AFTER THE PREFLT AND ENG RUNUP; I LOADED THE BAGGAGE; COMPLETED THE MANIFEST AND LOADED THE 3 PAX. USING THE STARTING ENGS CHKLIST; I NOTED THE 3 GREEN GEAR LIGHTS. AS THE R ENG STARTED THE NOSE GEAR RETRACTED. SEVERAL POSSIBILITIES EXIST FOR WHY THE GEAR RETRACTED. A POSSIBLE CORRECTIVE ACTION WOULD BE TO PLACE THE GEAR HANDLE DOWN PRIOR TO ENG STARTS. THIS WOULD ENSURE THE HANDLE POS; ENSURE THE GEAR SYS IS PRESSURIZED AND CHK THE FIRST HYD PUMP. MANUFACTURER CALLS FOR THE HANDLE TO BE PLACED DOWN AFTER THE FIRST ENG IS STARTED. THIS IS THE FIRST TIME THE GEAR HANDLE POS IS CHKED. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THAT GEAR DOORS CAN AND WERE OPENED MANUALLY WHEN ACFT WASHED AND SOME MAINT DONE. CONSENSUS IS THAT WATER GOT ON OR INTO THE SWITCH THAT ENERGIZED THE GEAR HORN AND ACTIVATES THE SOLENOID TO LNDG GEAR. THE WATER APPARENTLY CAUSED SWITCH TO FAIL. HE DOES NOT KNOW OF ANY OTHER INSTANCE; BELIEVES IT TO BE AN ISOLATED INSTANCE. PROP DAMAGE CREATED NEED TO TEAR DOWN THE ENG; PLUS SOME DAMAGE TO PITOT TUBE.