Here is the complete narrative of the circumstances of the hub failure on N233VA. The narrative was provided to Van's.
PROP HUB FAILURE IN FLIGHT
Vans Aircraft SLSA RV12 N233VA Serial # S12007 882 hrs TTSN Hobbs .
On, 6/19/2018, while flying from Big Bear California to Prescott, AZ, at 11500 ft. I experienced a harmonic vibration that was different than anything I have experienced in an RV12. Although running with some harmonic vibration, I was able to safely return to Prescott, AZ.
After returning, I removed the top cowl and the spinner. I suspected the prop but also checked the prop blade pitch. The blades had not moved. Checked the slipper clutch and it was at 456 Inch lbs. Checked the torque on the prop bolts and they were all at 240 inch lbs. While checking the torque on the prop bolts a crack was observed on the front hub. After further examination it was determined that there was a crack on both sides of the hub. Once the prop hub bolts were removed, the front hub fell off in two pieces.
The aircraft is equipped with a Sensenich Ground Adjustable Prop 2A0R5R70EN-V. Hub Serial Number 21193C , Blade Serial Numbers 34421/R70E and 34218 /R70E.
I contacted Sensenich and spoke with Don Rowell. He stated that there was a service bulletin for cracks in the hub of earlier model hubs, such as the one on my RV12. I told him the details of my experience and he asked me to send Sensenich the hub and blades. He advised that Sensenich would replace the Hub with a newer version and also replace the pins in the prop blades to fit the new version. Prop was a ďCĒ hub.
The Prop Blades and Hub were shipped to Sensenich for examination. Van's Aircraft was also notified of this incident.
I checked Vans Support site for bulletins/notifications and could not find any reference to Sensenich prop hubs on Rotax engines. I also checked Sensenich. and found one service bulletin (SB2016-06), "Inspection of adjustible pitch Jabiru hubs for cracks". It also references, "2 blade aircraft hubs with pitch cylinder for Jabiru or other direct drive engines". It does not mention Rotax Engines, which are a geared engine. However, this bulletin does show exactly the crack location and propagation of the cracks that occurred in this aircraft.
Feel free to contact me at 928-899-0277 or by email should you have further questions.
Robert J. Liddell
3110 Adobe Springs Drive
Prescott, AZ 86301