Belts coming off are far more frequent than impeller blades coming apart. The most common failure of a turbo is it's bearing going out. The only time I have ever seen a turbo come apart (been around turbo cars for a long while now), is when you use too small of a turbo and over speed it. I have however seen more than a fair share of Vortech super chargers have their impellers come apart and their gearboxes come apart. Remember that a Vortech supercharger is the same as a turbo with one exception----the driven side is done by the crank rather than the exhaust as is on a turbo. There are no roots type superchargers in airplanes that I have ever seen. Think of a roots type supercharger as a "blower."
Here is some of my experience with turbo's. I am the engine builder/assembler on this car (it's a family thing).
http://forums.jetcareers.com/member-announcements/86385-psca-outlaw-street-1st-place.html
