Trans-Canada Air Lines Flight 304 was a scheduled passenger flight between Chicago, Illinois, and Montreal, Quebec with intermediate stops at Toronto and Ottawa, Ontario. Flight 304 departed Chicago on an IFR flight plan at 13:04 and climbed to its cruising altitude of 19,000 feet, in accordance with its ATC clearance. The flight was routine until approximately 13:45, at which time the crew noted a momentary drop in rpm of the no. 4 engine, 200 to 300 below the normal cruise rpm of 13,600. Engine rpm returned to and remained normal for about five minutes, then No. 4 engine rpm was observed to increase rapidly to approximately 13,900 or 14,000. Shortly thereafter and concurrently with attempting to feather the propeller, the overspeed increased appreciably and feathering attempts, using both the manual and automatic systems, were unsuccessful. During and following attempts to feather, the airspeed decreased as did the sound of the No. 4 engine overspeed. The crew increased power on the remaining three engines and with the resultant increase in airspeed, the sound of No. 4 engine indicated its rpm was rising. Because of this development an emergency was declared at approximately 13:51 and clearance to descend wee obtained from the Traffic Control Center at Detroit. Power was reduced on Nos. 1, 2, and 3 engines, than an emergency descent was started and was continued at nearly maximum airspeed. At some time during this phase of the descent the crew depressurized the cabin. At approximately 13:53, at an altitude of about 9,000 feet, the No. 4 propeller broke loose and all four blades separated from the hub. One of the blades struck No. 3 engine, then passed through the passenger-occupied portion of the fuselage, killing one person and injuring several others. Descent was continued to about 3,000 feet, where power was again applied to Nos. 1, 2, and 3 engines. The rpm of No. 3 engine did not go above 11,500 and the fire warning came on. Although no fire was observed, the engine fire procedure, which includes feathering of the propeller, was successfully accomplished. The flight continued to Windsor, Ontario, where an emergency landing was made without further damage to the aircraft or injury to its occupants. Not until after landing did the pilots learn that a propeller blade had passed through the fuselage. Probable Cause: “The Board determines that the probable cause of this accident was the inflight separation of the No. 4 Propeller as a result of excessive loads induced by a descent at too high an airspeed while the propeller was windmilling decoupled from the engine and its r. p. m. was known to be uncontrolled.”