Propeller Separation During Cruise Leads to Forced Landing on Interstate Highway (N132BC)

Incident Overview and Pilot Report During a cruise at 1,200 feet, approximately thirty minutes into the flight, the pilot reported that the engine began to speed. Upon reducing the throttle, the pilot observed that the propeller assembly had separated from the engine. The pilot then selected an emergency landing area on a nearby Interstate highway. During the forced landing, the pilot attempted to fly under a bridge, resulting in a collision between the right wing of the airplane and the overpass structure. ## Airframe Examination and Component Recovery An examination of the airframe at the accident site confirmed that the propeller assembly had separated from the engine assembly. Investigators noted that the six propeller retention bolts were not present with the engine. Neither the propeller assembly nor the six propeller retention bolts were recovered for further examination. ## Assembly and Installation Details According to the pilot, the airplane was assembled in accordance with the kit instructions. The propeller assembly was installed on the engine and secured with six 5/16-inch coarse-threaded bolts that were provided.