B206L1, departing a rig with a load of "critters", when reduce power to cruise, engine surges, aircraft yaws, gauges dancing, the whole thing. I reduce power more, surge stops. Power back up to cruise, surge and yaw return. Landed atop nearest BIG quarters roof top pad. Roving maintenance works on it for 4 days, tightening fittings, replacing lines and various logical bits before they replace the starter-generator, which cures the engine surging...
Lost a generator in a B206B3, offshore, before Loran, much less GPS. Shed load, everything's working fine, hold a heading and a platform on the leg should appear out of the summer haze in couple minutes. No, it doesn't happen.
Ten minutes later, I recognize that I'm in a block 30+ degrees off my course line, and I "pilotage" home. What I didn't know is that losing the generator's current to the nose mounted battery changes the wet compass deviation, significantly.
I can remember a couple generator failures in an Astar, too, one of which was not alerted by the caution panel illuminating. At night, in an EMS bird, there's lots of power consumers, so it gets dark and quiet relatively quickly. In any case, by the time the voltage starts to drop, it's too late to save a useful amount of battery, sorta like waiting until the engine coughs to look for fuel.
Some starter/generator failures over the years, where the starter refused to drive. This is one event where a fit of temper might be useful, malletizing the starter sometimes re-seats the brushes, allowing a start and normal generator operation back to base. For the unfamiliar, "malletizing" means giving the offending device a whack, a satisfying process even when not efficacious.