Northeast Airlines’ Flight 812A departed Boston-Logan Field (BOS), at 20:42 on a VFR flight plan to Portland (PWM). The trip from Boston was routine and at 21:12 the flight contacted the Portland tower and received landing instructions: “Northeast 812 Able cleared to enter traffic pattern runway 20. Wind east variable southeast 5. The altimeter 2998. Check on base leg.” At 21:16 the flight reported turning into final approach and was cleared to land on runway 20. As the aircraft passed over the approach end of the runway, at an estimated altitude of 20 to 25 feet and an indicated airspeed of 120 mph, the throttles were brought back to what was expected to be the closed position, preparatory to landing. However, due to malfunctioning of the propeller reverse lock mechanism, the throttles were actually brought back beyond the closed position and into the propeller reverse pitch position Instead. This unexpected reversal of propeller pitch in flight resulted in an extremely hard landing 237 feet (72 m) past the approach end of the runway with serious damage to the aircraft. The airplane, however, continued along the runway a distance of 1,065 feet (326 m) from the point of initial impact before it came to rest. Fuel which had been spilled along the runway was ignited by sparks from the damaged aircraft and propellers scraping along the runway surface. All passengers were evacuated in an orderly manner through the rear cabin exit door. PROBABLE CAUSE: “The Board determines that the probable cause of this accident was failure of the throttle looking device to function properly thus permitting the movement of the throttles beyond the stop into the propeller reverse pitch position.”