Thankfully never had a real fire but a few spurious warnings on a number of different types, including one during a rotors running refuel.
Here's something that might be of interest to those flying Squirrel aircraft (might only be relevant to twins as I haven't flown the single engined ones). An interesting incident report was published in UK a couple of years ago but I feel it wasn't given enough emphasis at the time, so some pilots might be unaware of it.
Following an airborne FIRE warning light, a (UK Police) pilot carried out the appropriate drills, i.e. shut down the engine and fired off a bottle into the suspect engine. The FIRE warning remained lit so the second bottle was also fired into it. The light still remained on and then smoke appeared inside the cabin. The aircraft was understandably put down short of the airfield they were diverting to...scary stuff, especially as I believe it was dark at the time.
BUT it was a spurious fire warning! Worryingly, the smoke was actually caused by an overheated fire extinguisher system control circuit board inside the centre console. The smoke apparently occurred because the advice in the FM to "unlatch" the fire extinguisher buttons after firing the bottles hadn't been followed (in the heat of the moment?).
The AS-355 engine bay fire extinguisher buttons are of the "latching" (press ON / press OFF) type, in other words pressing them once leaves the button connected electrically, pressing it a second time unlatches it.
The fire bottles are fired by a "squib". This is actuated electrically on pressing the FIRE button, by blowing a built-in filament. The filament is supposed to burn through on actuation. However, sometimes it doesn't (as in this case) and the firing circuit stays intact and live connected unless the button is unlatched. The control circuit board isn't able to withstand a continuous current and so it may overheat, giving smoke and fumes in the cabin.
The UK CAA asked the manufacturers (now Eurocopter) to modify the system to prevent a recurrence. As far as I recall, they declined the request and there has not been a mandate so to do on UK registered aircaft. It seems to me that all that would be required to modify the aircraft is to fit a different type of firing switch, non-latching and spring loaded so that it returns to "OFF" when released.
Any Squirrel pilots NOT heard about this gotcha? I would be interested to know how effective the dissemination of the information was, as I've moved on to a different aircraft now. I must admit, that at the time I was flying the same type but I was unaware of the significance of that FM advice until then and it certainly had not been pointed out to me on my type training.
Be careful out there!