What was found
LGA - FLT 706 - AT 4,000 FEET, ON CLIMB-OUT, AFT CABIN FILLED WITH SMOKE, LAV SMOKE DETECTOR WENT OFF, TURNED RIGHT ACM OFF AND EMERGENCY RETURN TO LGA, SMOKE DISIPATED AFTER LANDING. REMOVED AND REPLACED NR 2 ENGINE. PERFORMED BURN OUT OF HIGH PRESSURE PNEUMATIC DUCTING. (M)