SA-227 FLT CREW EXPERIENCED UNSAFE LNDG GEAR WARNING DURING LNDG ROLLOUT. AFTER TAXIING CLEAR OF RUNWAY; TRUNNION PIN IS DISCOVERED TO BE MISSING.

Narrative

3RD LEG OF DAY ON ACFT; CAPT PNF; COPLT PF. VISUAL APCH ZZZ RWY 29; EVERYTHING NORMAL DURING APCH AND TOUCHDOWN; LNDG GEAR HORN STARTS TO SOUND DURING ROLLOUT (ALL 3 GEAR ON GND; WT ON WHEELS; LESS THAN 80 KTS) AND L MAIN GEAR LIGHTS START TO FLICKER BTWN GREEN AND RED. AS ACFT SLOWS TO SPD SLOW ENOUGH TO TURN ON 90 DEGS TAXI CONNECTOR; L MAIN LNDG GEAR LIGHT GOES SOLID RED; HORN STILL SOUNDING. CAPT MAKES TURN ON CONNECTOR; AND TAXIES STRAIGHT INTO NON-MOVEMENT RAMP AHEAD AND STOPS. PARKING BRAKE SET AND ACFT SHUT DOWN. UPON EXAM OF L MAIN LNDG GEAR WHEEL WELL; THE OUTBOARD TRUNNION PIN WAS FOUND MISSING; L MAIN LNDG GEAR WAS FOUND SLIGHTLY ASKEW; BUT STILL ATTACHED BY OPPOSITE PIN. PREFLT INSPECTION DISCOVERED NO ANOMALY; BUT NEITHER CREW MEMBER REMEMBERS LOOKING SPECIFICALLY AT THE BAT THAT IS THE SAFETY ON THE TRUNNION PIN. (PROC DOES NOT SPECIFICALLY SAY TO DO SO; ALTHOUGH IT WOULD BE GOOD PRACTICE) BECAUSE OF NORMAL OP OF GEAR DURING THE FLT; EXCEPT ROLLOUT; THE CREW THINKS THAT THE PIN MIGHT BE ON THE RWY IN ZZZ. ARPT OPS WAS CONTACTED; A VEHICLE DISPATCHED WITH AIRCREW AND ARPT OPS ONBOARD; AND TRUNNION PIN FOUND ON RWY NEAR TXWY A5 ALMOST TO EDGE OF GRASS/PAVEMENT ON L SIDE. MAINT CONTACTED; ACFT REPAIRED AND FERRIED BACK TO ZZZ1 FOR FURTHER INSPECTION.