What happened
The FAA’s narrative, in sentence case. The FAA writes it in capitals and removes private details.
While flying in the pattern near Chino Airport at 1400' AGL, the aircraft suddenly started shaking violently. The pilot immediately throttled the engine back to idle. The shaking diminished but was still there. He declared an emergency and returned to Chino Airport runway 26R. He landed without incident. Upon engine shutdown he saw that he lost over half of one propeller blade.
An SDR was submitted electronically (#2020FA0000348).
As the FAA filed it
WHILE FLYING IN THE PATTERN NEAR CHINO AIRPORT AT 1400' AGL, THE AIRCRAFT SUDDENLY STARTED SHAKING VIOLENTLY. THE PILOT IMMEDIATELY THROTTLED THE ENGINE BACK TO IDLE. THE SHAKING DIMINISHED BUT WAS STILL THERE. HE DECLARED AN EMERGENCY AND RETURNED TO CHINO AIRPORT RUNWAY 26R. HE LANDED WITHOUT INCIDENT. UPON ENGINE SHUTDOWN HE SAW THAT HE LOST OVER HALF OF ONE PROPELLER BLADE.
AN SDR WAS SUBMITTED ELECTRONICALLY (#2020FA0000348).