What happened
Shortly after takeoff, the crew of the aircraft heard a loud noise accompanied by a slight vibration originating from the left propeller. In response to these symptoms, the crew performed a return to the airport and landed the aircraft safely. No injuries were reported.
Upon inspection, it was discovered that a portion of the propeller erosion shield had debonded from the blade. This fragment penetrated the passenger cabin just aft of the airstair door, struck the Passenger Service Unit at Seat 1A (knocking it ajar), and ricocheted off the ceiling before penetrating the inner window pane at Seat 2C.
The investigation
A laboratory examination of the propeller blade identified an area consistent with adhesive disbonding covering approximately 80% of the total bond area. Records indicated that the blade had undergone an overhaul and repair 300 flight hours prior to the accident. The examined repaired area contained several voids, air bubbles, dirt, and debris.
Investigators also found evidence of chafing at multiple locations within the debonded area, which indicated movement between the propeller blade body and the erosion shield. Testing of samples from the erosion shield adhesive revealed that the components had been mixed in improper proportions, which resulted in reduced bond strength.