The pilot reported that the landing gear 'in-transit' light had remained on after the gear was selected up on departure from Palm Island. The gear was cycled twice, but the 'in-transit' light remained illuminated on each occasion. The pilot decided to return the landing gear to the down position and continue the flight to Townsville. After a normal approach and touchdown the pilot noticed that the aircraft was settling low on the left side. The left landing gear then collapsed and the aircraft skidded to a halt on the runway. Both the pilot and passenger exited the aircraft safely. Examination of the aircraft found that the forward pivot shaft which locates and secures the left landing gear trunnion assembly to the airframe casting had come loose and moved out of position. The dislocation of this shaft allowed the left gear to collapse as the landing loads were applied. Investigation revealed that the safety fastener roll pin which holds the pivot shaft in place had broken, allowing the pivot to move out of place. The safety lock wire which passes through the roll pin was found to be still in place, but had separated at the point where the roll pin broke. The Civil Aviation Authority is undertaking specialist metallurgical examination of the failed components.