Flight Crew Commercial; Flight Crew Multiengine
Flight Crew Last 90 Days 107; Flight Crew Total 1365; Flight Crew Type 1014
Aircraft Equipment Problem Critical
Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Landed in Emergency Condition; General Maintenance Action
Aircraft
I was cruising at 8;000 ft. I was on an IFR flight plan talking to ZZZ Approach. Conditions were VFR; good visibility; no clouds; a little low lying fog in the valleys. All of a sudden I got an immediate and strong vibration. Initially I checked the engine instruments and everything appeared normal. I turned on the fuel pump and pushed the mixture full rich. I also pulled the throttleback to 'ease' the vibration; no significant change. I changed the propeller speed and that changed the vibration; but did not make it go away. I was able to maintain airspeed and altitude and alerted ZZZ Approach that I had [requested priority handling] and was diverting ZZZ1. I was not within gliding distance; but would be in about 3 miles (1 minute). I told ZZZ of my fuel (35gal) and souls on board (1). Once I had the airport in sight I told ZZZ of my intentions to fly over the field at 8;000 ft. and then start circling down to land. I began descending and pulled the power back further which further increased the vibration. I noticed the nose gear transit light was lit; and that the gear system had low pressure. I moved the gear switch to the down position and nothing happened. I moved the gear selector back to the up position and nothing happened. I checked the circuit breakers and noticed the landing gear pump had tripped. I reset it and extended the gear normally; three green. At this point I was about 2;600 ft. MSL on downwind at about 100 kts. I started putting the flaps out to add some drag and get lower. Any power changes made the vibration worse. On short final I pulled the power back and the vibration got really bad. Over the numbers I could not move the control stick it was shaking so badly. I turned off the mags and landed while the engine stopped. After the engine stopped the vibration went away and I could see part of the propeller blade was missing.I taxied off the runway just using the momentum and I had and cleared the hold short line. The fire and police were waiting at the intersection; and were a big relief to see.  After I gave them my driver license and told them what happened; we pulled the plane using the tow bar onto the ramp. Upon inspection of the fracture surface; there was evidence of corrosion 1/8 in. back from the leading edge indicating the crack had existed for some time.  I had recently dressed the prop during a conditional inspection; but did not see the crack.  About 6 in. of one of the two blades had departed in flight.  The prop had been overhauled about 10 years prior by a reputable shop and had 960 hours time in service.
Pilot reported vibration during cruise of an undetermined origin. After successful diversion it was discovered several inches was missing from one of the propeller blades that had been repaired years earlier and recently inspected.