I've always been told that it's perfectly safe for an engineer/mechanic to ground run helicopters. What has always made me have a different opinion is that post maintenance ground runs are when mistakes might easily be made, not least because the engineering requirements might be at variance with a normal start configuration. I got caught out once in a twin when the aircraft suddenly began "padding" laterally after the first engine start, just as the rotors came up to speed. I had to lift off immediately, single engine, to prevent ground resonance, which very much surprised the ground crew standing just outside the rotor disc and resulted in an MOR being filed. I know of an almost identical incident where the aircraft was badly damaged, not because the aircraft was lifted off, but because it was put back down again "rather enthusiastically".
Last edited by ShyTorque; 13th March 2018 at 17:10.