Cessna 208B Grand Caravan
Out Of Balance
During cruise, aircraft experienced excessive vibration. Reducing propeller speed cleared the vibration for a short time but as the flight continued, vibration returned. Declared an emergency and landed without incident. External visual inspections failed to note defects. Propeller (p/n 3GFR34C703) was dynamically balanced with 28.4 grams of weight. A test flight was performed after the propeller was balanced with no vibration noted.
Part total time: 8244.0 hours
Propeller was reported to not go into feather. There was no evidence of a bird or blade strike. Examination revealed blades were corroded and/or cracked in the bearing race area. Installed new hub and blades and retained new blade bearings installed at last overhaul.
Part total time: 14,553.0 hours
Piper PA-44-180 Seminole
During a 100-hour inspection, a technician found the propeller low-pitch stop threads stripped. The safety wire is still in place.
Part total time: 379.0 hours
Propeller Departed Airplane
After landing, the pilot discovered that the propeller departed in-flight. The pilot indicated that the propeller was removed during the previous annual inspection, but there is no logbook entry. The propeller was found three days later approximately eight miles from the accident site. All bolts were found in the propeller spinner; two of the bolts sheared off of the propeller hub. The bolt threads of the other four bolts were undamaged. All of the bolts have some safety wire attached. It appears the bolts may have been safety-wired in pairs.
Part total time: Unknown
Pilot reported in-flight vibration. On landing, pilot smelled wood smoke. Inspection of composite propeller and hub found soot escaping from behind forward crush plate and hub bolts finger tight. Removal of front crush plate found three of eight bolts missing bolt heads and exhibiting granular structure consistent with hydrogen embrittlement. Damage to one blade face consistent with a metal object, like a separated bolt head, striking the prop. Removal of propeller and hub showed charring of the propeller between the hub and crush plates.
Part total time: 71.0 hours