Samoa Air flight 906, a DHC-6-200, N719AS, veered off the runway and collided with a ditch and an embankment while landing at Fitiuta, Tu’a, American Samoa. The aircraft sustained substantial damage; however, neither of the 2 flight crewmembers nor any of their 12 passengers were injured. The flight originated from Pago Pago, American Samoa, at 06:09 as a regularly scheduled non-stop domestic passenger flight to Fitiuta. Visual meteorological conditions prevailed at the time and a composite IFR/VFR flight plan was filed. The captain overflew the Fitiuta airfield to assess winds conditions and the windsock indicated a quartering headwind for runway 12. During rollout the airplane veered immediately right when the power levers were brought into beta. The captain corrected with rudder and braking but was unable to maintain directional control. The aircraft ran off the right side of the runway and collided with a ditch and an embankment. After deplaning, the crew found that the winds were a 60-degree tailwind on runway 12. The windsock’s pivot point on the pole was rusted and would not rotate. The aircraft with the same landing weight and a 60-degree 10-knot tailwind would require a 1,600-foot landing roll on the 2,350-foot runway without the assistance of both props in beta. The beta pin had backed out of position on the left engine’s beta control linkage. The beta pin, cotter pin, and washer were found in the bottom of the engine cowling. The left engine had been changed 2 days prior to the accident. As the mechanics finished the beta pin area during engine installation, the inspector checked the area and found that the pin was in place and properly safety wired. Following the inspector’s signoff of the area, the mechanics discovered that the teleflex cable was too short for the beta valve to be flushed and subsequently had to be adjusted. The director of maintenance readjusted the cable, which required disturbing the safety wire on the beta pin. One of the two mechanics that had been instructed to re-safety the connections after the adjustment thought that the rear portion had already been safetied and did not recheck the area. The inspector believed the area had already been checked and did not re-examine the beta pin. The mechanical separation of the left engine beta control linkage during landing rollout, which resulted in asymmetrical decelerative action and the pilot’s subsequent inability to maintain directional control. The separation of the linkage was due to the airline’s inadequate inspection and quality assurance procedures. An inoperative windsock pivot point, which resulted in faulty wind direction information to the flight crew was a factor in this accident.