AFTER TAKEOFF PLT OBSERVED THAT THE AIRSPEED INDICATOR WAS INDICATING LOW, AND THAT THE ACFT WAS BANKING TO THE RT UNCOMMANDED. HE LANDED FAST AT AN ARPT 12 NM AWAY, TRAVELLED OFF THE END OF THE RWY, AND COLLIDED WITH BUSHES. FUEL IMBALANCE WAS NOT A FACTOR. A MECHANIC WHO REPAIRED THE ACFT REPORTED THAT THE PITOT STATIC SYSTEM WAS PARTIALLY BLOCKED BY CONTAMINANTS. THE RIGGING OF THE AILERONS AND FLAPS CHECKED SATISFACTORY.