WHILE ON A LOCAL FLIGHT, THE PILOT EXECUTED A STEEP DESCENDING TURN TO APPROXIMATELY 150 AGL, TO OVERFLY THE PASSENGER'S HOUSE. SHORTLY AFTER LEVELING AT 150 FEET, WITH 'SLOW FORWARD AIRSPEED,' THE HELICOPTER MADE A 'SUDDEN QUICK TURN TO THE RIGHT AND PITCHED NOSE DOWN...,' DESCENDING INTO TREES. THE WIND AT THE TIME OF THE ACCIDENT WAS CALM. ACCORDING TO THE HEIGHT VELOCITY DIAGRAM FOR THE HUGHES 269A, OPERATION OF THE HELICOPTER AT 150 FEET AND ZERO TO 52 KNOTS OF INDICATED AIRSPEED SHOULD BE AVOIDED.