Prinair Flight-303, a de Havilland DH-114, was a scheduled air taxi flight from San Juan to Mayaguez, Puerto Rico. There were nine passengers and two crewmembers aboard when the airplane was taxied to the runway at San Juan International Airport for takeoff. After the aircraft was taxied out, the flightcrew completed the routine engine runup and checklist. They noted roughness when the Nos. 2 and 3 engines were checked; both engines were rechecked, and the takeoff clearance was requested and received. Takeoff power was applied slowly and by the time full throttle power was set, the airplane had accelerated to between 30 and 40 knots. At this time, the flightcrew heard a loud explosive sound, and the airplane veered to the right. Power was reduced immediately, but directional control was difficult to maintain. The captain, however, was able to keep the airplane on the runway. The first officer notified San Juan Tower that the takeoff was being aborted; the tower was also advised that an emergency existed and equipment was requested. The airplane was brought to a complete stop and the flightcrew initiated the emergency evacuation of the passengers. Although all emergency shutdown procedures were completed for the four engines, including the closing of all four mixture controls, and fuel shutoff valves and the turning of magneto switches to the “off” position, the Nos. 1 and 2 engines continued to run. The feathering controls were partially jammed, but after several attempts the No. 1 engine propeller was feathered and stopped. Attempts to shut down No. 2 engine in this manner were unsuccessful, and attempts to change the fuel system cross-feed configuration to terminate the fuel supply also were unsuccessful. The No. 2 engine continued to run for about 10 minutes after the takeoff was discontinued. Because of concern that an engine fire might develop, the four fire extinguishing systems were discharged, after which the No. 2 engine stopped. The captain then also evacuated the airplane. Probable Cause: “The National Transportation Safety Board determines that the probable cause of the accident was the separation of the No. 1 propeller blade of the No. 2 propeller assembly. The blade separated as a result of vibratory stresses which induced fatigue cracks not readily detectable during routine preflight inspections. Contributing to the accident were inadequate overhaul inspection procedures at a certificated repair station and inadequate dissemination and enforcement of recommended maintenance practices by the Federal Aviation Administration.”