PA23 MAIN GEAR COLLAPSES UPON ENG START AT LGB.

Narrative

PRIOR TO STARTING THE ENG; THE ACFT WAS MOVED FROM THE TIE-DOWN POS FOR START-UP. BEFORE STARTING THE ENGS; I INTENDED TO PUT THE LNDG GEAR LEVER IN THE DOWN POS. AS I REACHED FOR THE GEAR LEVER; I WAS DISTR BY A PERSON WALKING NEAR THE AIRPLANE. WITHOUT RECHKING THE GEAR LEVER; THE R ENG WAS STARTED AND THEN THE L ENG WAS STARTED. THE L ENG IS THE ONE WITH THE HYD PUMP. THE R GEAR RETRACTED CAUSING A PROP STRIKE AND MINOR SKIN DAMAGE. ON RECOVERY THE L MAIN AND NOSE GEAR WERE CHKED; AND WERE DOWN AND LOCKED AND BOTH GEAR INDICATING LIGHTS WERE ON. WHEN THE R SIDE WAS RAISED; THE L GEAR PARTLY RETRACTED CAUSING MINOR DAMAGE. THE L PROP AND ENG WERE OK. THE PLANE WAS REPOSITIONED IN THE TIE-DOWN WITHOUT FURTHER PROBS. CONTRIBUTING FACTORS: 1) ANTI-RETRACTION DEVICE ON THIS OLDER ACFT DID NOT FUNCTION. 2) THE DISTR OF SOMEONE WALKING BY THE PLANE. CORRECTIVE ACTION: 1) DOUBLECHK GEAR LEVER POS AND OTHER CTLS BEFORE STARTING THE ENGS. 2) REPAIR OR REPLACE ANTI-RETRACTION VALVE. 3) RETEST THE ANTI-RETRACTION VALVE DURING INSPECTIONS. NOT A RPTABLE ACCIDENT.