Ch 7 news said that the pilot had radioed to advise of a warning light in the cockpit. Eyewitness said there was a loud bang but no fire, and bits fell off it.
How many warning lights are there in a Robby? One for the generator not on line (not likely to cause an accident), one for the clutch light - if it drove too tight it could snap a belt, or if it disengaged you lose revs or go into auto.
But it sounds like the rotor hit the tail boom. Not a recommended practice. Very sad for F. and his student and families.