Mechanics can do ground runs after being properly trained and certified for those procedures.
SASless, thanks for the clarification. Only question here is, how much training should a mechanic have to carry out such procedures? If a helicopter develops ground resonance, as has been suggested in this case, there are generally only two ways to cancel it out - shut down or lift off, dependant on where you are in the rpm band etc. I doubt if any mechanic would receive sufficient training to do the latter, so kind of limits the options.......