LNDG GEAR COLLAPSES ON ROLLOUT AFTER LNDG.

Narrative

WHILE TAXIING AFTER LNDG; ACFT STARTED VEERING R AND DESPITE IMMEDIATE APPLICATION OF L BRAKE AND RUDDER; ACFT DID NOT RESPOND. AND ONLY AFTER APPLICATION OF FULL PWR DID ACFT STOP YAWING TO R WHEN L LNDG GEAR COLLAPSED. THE L BRAKE APPARENTLY MALFUNCTIONED SINCE THE INITIAL YAWING TO THE R WAS NOT SEVERE AND SHOULD HAVE BEEN CORRECTABLE WITH L BRAKE AND RUDDER. THE ACFT HAD YAWED APPROX 45 DEGS WHEN THE L GEAR COLLAPSED. FORTUNATELY THE GEAR COLLAPSED IN FRONT OF THE WING STRUT; SO THERE WAS NO DAMAGE TO WING STRUTS; ONLY WING TIP DAMAGE. CONTRIBUTING FACTORS: ACFT IS EQUIPPED WITH TUNDRA TIRES WHICH MAKES HANDLING ON HARD-SURFACED RWYS MORE DIFFICULT. ALSO; THERE IS A POSSIBILITY THAT THE REAR-SEAT PAX COULD HAVE INADVERTENTLY ACTIVATED AND/OR HELD R BRAKE WHICH COULD HAVE INITIATED VEERING TO THE R AND MAY HAVE COUNTERED L RUDDER AND BRAKE CORRECTIVE ACTION. WIND WAS NOT A FACTOR. UPON ENTERING DOWNWIND; PLT NOTED THAT WINDSOCKS ON BOTH ENDS OF RWY INDICATED A LIGHT WIND STRAIGHT DOWN RWY. AFTER PLT AND PAX EXITED ACFT BOTH WINDSOCKS STILL INDICATED A LIGHT WIND STRAIGHT DOWN RWY. CORRECTIVE ACTIONS INCLUDE: INSTALLATION OF GUARDS TO PREVENT REAR PAX FROM BEING ABLE TO ACTIVATE BRAKES; EITHER INTENTIONALLY OR INADVERTENTLY. ALLOW ACFT WITH OVERSIZE TIRES TO OPERATE ON GRAVEL SHOULDERS OF RWYS; TXWYS; OR EVEN ADJACENT ROADS OR GRASSY INFIELDS 'AT THEIR OWN RISK;' THE SAME WAY HELIS ARE ALLOWED TO TKOF AND LAND AT 'THEIR OWN RISK' AT VARIOUS LOCATIONS AT ARPTS (OTHER THAN RWYS). THIS WOULD ALLOW THE PLTS OF SPECIALLY EQUIPPED ACFT (OR ACFT WITH LIMITED XWIND CAPABILITIES) TO CHOOSE THE MOST SUITABLE LNDG AREA FOR THEIR ACFT.